THE POLARITY OF A MOLECULE BASED ON ITS STRUCTURE
At the end of the lesson, you should be able to determine if a molecule is polar or nonpolar given its structure.
Did you know that such molecule may exhibit polarity based on its 3-dimensional shape? There are millions of different molecules, and there are many ways to sort them. One way to classify them is bas ed on polarity. Polarity means having dipoles, a positive and a negative end. Based on polarity, molecules can be polar or nonpolar. Polar molecules have dipoles. Their dipole moments do not add up to zero (or do not cancel out). Water and carbon monoxide are examples of polar molecules. Nonpolar molecules do not have positive or negative ends. Their dipole moments add up to zero (they cancel out). Carbon tetrachloride and methane are examples of nonpolar molecules. Generally, you can tell if a molecule is polar or nonpolar based on: its structure or shape the polarity of the individual bonds present in the molecule
Steps in Determining the Polarity of a Molecule Draw the correct Lewis structure and molecular geometry of the molecule. Identify the polarity of each bond present in the molecule. A bond is polar when the atoms in the bond have different electronegativities. Recall that electronegativity is the measure of the tendency of an atom to attract a bonding pair of electrons. (You may use the periodic table to determine the electronegativity values of the atoms.) Draw the dipole moment vectors for polar bonds. The dipole moment vector points to the more electronegative atom.
Determine the sum of the dipole moment vectors. If the dipole moments cancel out each other, the molecule is nonpolar; otherwise, it is polar.
Example 1 Carbon dioxide (CO2) is the gas that you exhale. Correct Lewis structure and geometry:
Oxygen is more electronegative than carbon. Therefore, the C —O bonds are polar.
Since CO2 has a linear symmetrical structure, the dipole m oments of the C —O bonds cancel out.
CO2 is a nonpolar molecule.
Example 2 Sulfur dioxide (SO2) is a colorless toxic gas formed by burning sulfur in air. Correct Lewis structure and geometry:
Oxygen is more electronegative than sulfur. Therefore, the S —O bonds are polar.
Since the molecule is bent-shaped, the dipole moments do not cancel out.
SO2 is a polar molecule Note that the shape or structure does not directly determine whether the molecule is polar or nonpolar. However, you need to know the shape of the molecule to know if the dipole moments cancel out. Consider the examples below to help you understand the concept of polarity. Below are the images of a magnet bar, a block of wood, and a battery.
Which of the three show(s) polarity?
Ammonia (NH3) is a colorless gas. A solution of ammonia in water is used as a cleaning agent. Determine if ammonia is polar or nonpolar. Key Points Polarity means having dipoles, a positive and a negative end. Based on polarity, molecules can be polar or nonpolar. Polar molecules have dipoles. Their dipole moments do not add up to zero (or do not cancel out). Nonpolar molecules do not have positive or negative ends. Their dipole moments add up to zero (they cancel out). In general, you can tell if a molecule is polar or nonpolar based on the shape of the molecule and thepolarity of the individual bonds present in the molecule.
THE PROPERTIES OF A MOLECULE BASED ON ITS POLARITY
At the end of the lesson, you should be able to relate the polarity of a molecule to its properties.
Why is sucrose (table sugar) soluble in water? In the previous lesson, you have learned that both sucrose and water are polar molecules. In this lesson, you will continue to learn about polar and nonpolar molecules. But this time, y ou will relate the polarity of the molecules to their observable properties. The properties of the molecules are related to their polarity. To understand the relationship, you must be able to describe the force of attraction between the molecules.
Polar molecules have partially positive and negative ends. When two polar molecules are near each other, th e negative end of one molecule is attracted to the positive end of the other. The separation of charges result in a strong force of attraction between the molecules. On the other hand, nonpolar molecules do not have positive or negative ends. Between two n eighboring nonpolar molecules, the attraction is very minimal.
How do you relate the strength of attraction between the molecules to their observable properties? Solubility Do you remember the rule of thumb “ like dissolves like” in your previous Chemistry lessons? This rule is applied on the concept of solubility of molecules. Polar solutes dissolve in polar solvents. For example, sucrose is soluble in water because both of them are polar molecules. On the other hand, nonpolar solutes dissolve in nonpolar solvents. For example, hexane ( C6H14) and benzene (C6H6) are nonpolar molecules because they only contain nonpolar C-H bonds. The combination of these molecules form a solution.
Melting point Melting point is the temperature at which a solid turns into liquid. Heat is needed to break the forces of attraction between the molecules. Because the polar molecules have relatively stronger forces of attraction compared to nonpolar ones, greater amoun t of heat must be applied to break these forces. Therefore, in general, polar molecules have higher melting points than
nonpolar molecules . For example, hydrogen fluoride ( HF) is polar while fluorine ( F2) is nonpolar. HF has higher melting point than F2. Boiling point Boiling point is the temperature at which a liquid turns into gas. Similar to melting point, greater amount of heat is needed to break the forces of attraction of polar molecules compared to nonpolar ones. Generally, polar molecules have higher boiling points than nonpolar molecules . For example, methanol ( CH3OH) is a polar molecule while methane ( CH4) is nonpolar. The CH3OH is higher than that of CH4. boiling of CH3OH Study the illustrations below to compare a polar and a nonpolar molecule. Water molecules are polar. The partially negative end of one molecule is attracted to the partially positive end of another molecule.
Carbon dioxide molecules are nonpolar. There is a minimal f orce of attraction between the molecules.
SO2 is a polar molecule Note that the shape or structure does not directly determine whether the molecule is polar or nonpolar. However, you need to know the shape of the molecule to know if the dipole moments cancel out. Consider the examples below to help you understand the concept of polarity. Below are the images of a magnet bar, a block of wood, and a battery.
Which of the three show(s) polarity?
Ammonia (NH3) is a colorless gas. A solution of ammonia in water is used as a cleaning agent. Determine if ammonia is polar or nonpolar. Key Points Polarity means having dipoles, a positive and a negative end. Based on polarity, molecules can be polar or nonpolar. Polar molecules have dipoles. Their dipole moments do not add up to zero (or do not cancel out). Nonpolar molecules do not have positive or negative ends. Their dipole moments add up to zero (they cancel out). In general, you can tell if a molecule is polar or nonpolar based on the shape of the molecule and thepolarity of the individual bonds present in the molecule.
THE PROPERTIES OF A MOLECULE BASED ON ITS POLARITY
At the end of the lesson, you should be able to relate the polarity of a molecule to its properties.
Why is sucrose (table sugar) soluble in water? In the previous lesson, you have learned that both sucrose and water are polar molecules. In this lesson, you will continue to learn about polar and nonpolar molecules. But this time, y ou will relate the polarity of the molecules to their observable properties. The properties of the molecules are related to their polarity. To understand the relationship, you must be able to describe the force of attraction between the molecules.
Polar molecules have partially positive and negative ends. When two polar molecules are near each other, th e negative end of one molecule is attracted to the positive end of the other. The separation of charges result in a strong force of attraction between the molecules. On the other hand, nonpolar molecules do not have positive or negative ends. Between two n eighboring nonpolar molecules, the attraction is very minimal.
How do you relate the strength of attraction between the molecules to their observable properties? Solubility Do you remember the rule of thumb “ like dissolves like” in your previous Chemistry lessons? This rule is applied on the concept of solubility of molecules. Polar solutes dissolve in polar solvents. For example, sucrose is soluble in water because both of them are polar molecules. On the other hand, nonpolar solutes dissolve in nonpolar solvents. For example, hexane ( C6H14) and benzene (C6H6) are nonpolar molecules because they only contain nonpolar C-H bonds. The combination of these molecules form a solution.
Melting point Melting point is the temperature at which a solid turns into liquid. Heat is needed to break the forces of attraction between the molecules. Because the polar molecules have relatively stronger forces of attraction compared to nonpolar ones, greater amoun t of heat must be applied to break these forces. Therefore, in general, polar molecules have higher melting points than
nonpolar molecules . For example, hydrogen fluoride ( HF) is polar while fluorine ( F2) is nonpolar. HF has higher melting point than F2. Boiling point Boiling point is the temperature at which a liquid turns into gas. Similar to melting point, greater amount of heat is needed to break the forces of attraction of polar molecules compared to nonpolar ones. Generally, polar molecules have higher boiling points than nonpolar molecules . For example, methanol ( CH3OH) is a polar molecule while methane ( CH4) is nonpolar. The CH3OH is higher than that of CH4. boiling of CH3OH Study the illustrations below to compare a polar and a nonpolar molecule. Water molecules are polar. The partially negative end of one molecule is attracted to the partially positive end of another molecule.
Carbon dioxide molecules are nonpolar. There is a minimal f orce of attraction between the molecules.
Based on the interaction of molecules, water is expected to have higher melting and b oiling points than carbon dioxide. Below are the actual melting and boiling points o f the compounds.
Tips Molecular weight is also a factor in assessing the melting and boiling points of molecules. For example, carbon monoxide (CO) is a polar molecule. However, it has a lower boiling point (−191.5 C) compared to hexane (BPofC6H14=68 C) because its molecular weight is much lower. You will learn more about this in the next lessons. Key Points Polar molecules have stronger attractive forces compared t o nonpolar molecules. In general, polar molecules have higher boiling and melting points compared to nonpolar ones. “Like dissolves like .” Polar solutes dissolve in polar solvents while nonpolar solutes d issolve in nonpolar solvents. ∘
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TYPES OF INTERMOLECULAR FORCES OF ATTRACTION
At the end of the lesson, you should be able to describe the general types of intermolecular f orces of attraction.
What are the types of intermolecular forces that can be present between molecules? Intermolecular forces are the attractive forces present between molecules. Generally, they are called van der Waals forces, named after the Dutch scientist Johannes van der Waals. The different types of intermolecular forces of attraction (IMFA) are: London dispersion forces (LDF) Dipole-dipole forces Hydrogen bonding London dispersion forces present in all molecules caused by fluctuations in the electron distribution within atoms or molecules weak type of IMFA
Example In a nonpolar molecule, such a s O2, there are no positive o r negative ends. However, the electrons of this molecule a re constantly moving. There are times when electrons move to one end, making such end partially negative while the other end becomes partially positive. Hence, the molecule can have an instantaneous dipole .
The temporary dipole of a molecule induces instantaneous dipoles on neighboring molecules.
Tip In assessing the relative strengths of London dispersion forces between two different substances, compare their molecular weight and size. Larger and more massive molecules a re more polarizable (i.e. they have a greater tendency to have distorted electron clouds) and have stronger IMFA. Dipole-dipole forces attractive forces between polar molecules result of the electrical interactions among dipoles on neighboring molecules moderately strong type of IMFA Example HCl is a polar molecule. It has partially positive and partially negative ends.
The partially positive end of the molecule is attracted to the partially negative side of another molecule.
Tip In assessing the relative strengths of dipole-dipole forces b etween two different substances, compare their polarities. A more polar substance will have stronger dipole –dipole forces compared to a less polar one. Hydrogen bonding a special kind of dipole-dipole force an attractive force between a hydrogen atom of one molecule and a highly electronegative atom (O, N, or F) of another molecule strongest type of IMFA
Example Consider the water molecule, H2O.
The hydrogen of one molecule is attracted to the oxygen atom of another molecule.
During respiration, we inhale oxygen gas (O2) and exhale carbon dioxide (CO2). Why do you think these compounds exist as gases at room temperature?
Key Points Intermolecular forces are the attractive forces between molecules. The three types of IMFA are L ondon dispersion forces, dipole-dipole forces, and hy drogen bonding.
THE PROPERTIES OF A SUBSTANCE AS EFFECT OF INTERMOLECULAR FORCES OF ATTRACTION
At the end of the lesson, you should be able to explain the effect of intermolecular forces on the properties of substan ces. Recall the different types of intermolecular forces of attraction: London dispersion forces (LDF) – present in all molecules Dipole – dipole forces – present in polar molecules Hydrogen bonding – present in molecules with a hydrogen bonded to a n electronegative atom (O, N, or F) How are these intermolecular forces related to the observable properties of different substances? The properties of molecules depend on the type and strength of their intermolecular forces of attraction. Properties Dependent on IMFA Phase at room temperature When molecules have strong intermolecular forces of attraction, they are packed close together. They often exist as co ndensed phase (solid or liquid) at room temperature. When molecules have weak intermolecular forces of attraction, they are far apart from each other. They often exist as gas at room temperature. Solubility Solubility refers to the ability of a substance to dissolve in a given amount of solvent at a specified temperature. Recall the rule “ like dissolves like.” When the solute and the solvent both exhibit the same intermolecular forces of a ttraction, they form a solution.
Examples Water and ethanol are polar substances. They both exhibit LDF, dipole - dipole forces, and hydrogen bonding. When mixed together, they form a solution.
On the other hand, hexane and water do not have similar intermolecular forces of attraction. The only attractive forces present in hexane are the relatively weak London dispersion forces. These forces ca nnot significantly disrupt the strong hydrogen bonding among water molecules. Therefore, hexane and water form a heterogeneous mixture.
Melting point Melting point is the temperature at which the substance changes from solid to liquid. Stronger intermolecular forces means greater amount of energy is needed to break the attractive forces between molecules. Substances with stronger IMFA have higher melting points compared to those with weaker IMFA. Boiling point Boiling point is the temperature at which the substance changes from liquid to gas. Similar to melting point, stronger intermolecular forces means greater amount of energy is needed to break the attractive forces between molecules. Substances with stronger IMFA have higher boiling points compared to those with weaker IMFA. Surface Tension Surface Tension is the tendency of a fluid to acquire the least possible surface area. Molecules with stronger intermolecular forces will exert greater cohesive forces and acquire less surfa ce area ( higher surface tension) than those with weaker IMFA. Viscosity Viscosity is the measure of a fluid’s resistance to flow. Molecules with stronger intermolecular forces have greater resistance to flow, and thus, higher viscosity compared to those with weaker IMFA. Vapor Pressure Vapor Pressure is the pressure exerted by a vapor in equilibrium with its liquid phase in a closed sy stem. Molecules with stronger intermolecular forces have less tendency to escape as gas, and thus lower vapor pressure compared to those with weaker IMFA. Strengths of Intermolecular Forces When comparing the strengths of intermolecular forces, check the difference in molecular weight. If the difference is t oo large (>1000), then generally, the molecule with greater molecular weight has stronger intermolecular forces. Otherwise, you may use the following strategy: Check which molecule exhibits hydrogen bonding. This molecule will have stronger intermolecular forces. Check which molecule is polar. Polar molecules have stronger intermolecular forces. Compare London dispersion forces. More massive molecules have stronger intermolecular forces.
Example 1 Which has higher boiling point, H2Oor H2S? Answer: H2Oexhibits hydrogen bonding. It has stronger intermolecular forces. Therefore, it has higher b oiling point than H2S. Example 2 Which is most likely solid, F2 or I2? Answer: Both fluorine and iodine are nonpolar molecules. They exhibit London dispersion forces only. Because iodine has higher molecu lar mass, it has stronger London dispersion forces. It is most likely to be solid. (Indeed, I2 is solid while F2 is gas at room temperature.
Key Points The properties of molecules depend on the type and strength of their intermolecular forces of attraction. “Like dissolves like. ” When the solute and the so lvent both exhibit same intermolecular forces of attraction, they form a solution. When comparing properties, stronger intermolecular forces result in higher boiling and melting points, higher viscosity, high er surface tension, and lower vapor pressure. Increasing strengths of IMFA: London dispersion forces, Dipole-dipole f orces, H-bonding
THE USES OF DIFFERENT MATERIALS ACCORDING TO THEIR PROPERTIES AND STRUCTURES: MEDICAL IMPLANTS
At the end of the lesson, you should be able to relate the properties and structures of medical implants to their function. Atoms and molecules combine to form hundreds of thousands of different materials people use every day. The properties of thes e materials are influenced by their chemical structures. In turn, their properties determine their uses. In this lesson, you will focus on the materials used for medical implants. How are the basic structures of implants related to
their properties and uses? A medical implant is a chemical substance or a device used to replace, support, or improve a part of the human body. It should be stable, inert, heat-resistant, biocompatible, and long-lasting.
Materials Used for Medical Implants In general, the materials used for implants can be categorized into three, namely, metals, ceramics, andpolymers.
Metals Metals have particles that are held together by strong metallic bonds. They are strong and durable. They are a lso good conductors of electricity because of the free flo wing electrons.
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Alloys are combinations of one or more metals held together by metallic bonds. They contain atoms that ha ve different sizes, which distort the regular arrangement of atoms. This distortion makes it more difficult for the layers of atoms to slide over each other, so alloys are harder and stronger than most pure metals.
Examples Alloys are often used for load- bearing implants because of their high strength, durability, and inertness. For example, stainless steel is one of the most common alloys used in orthopaedic implants, which are medical devices that can replace a missing joint or support a damaged bone. Pure metals can also be used as implants. Pure titanium is best used as a pacemaker case. A pacemaker is a device which uses electrical impulses to regulate heart beats. Titanium is used because of its high resistance to corrosion and superior biocompatibility.
Ceramics Ceramics are nonmetallic, inorganic solids with ionic or covalent bonds. They are commonly used in dental implants, such as crowns, cement, and dentures. They are hard, inert, and durable materials.
Example Zirconia ceramic (ZrO2) is a crystalline solid held together by covalent bonds. The strong bonds and the regularity of the cr ystalline structure give rise to the high strength and toughness of the material.
Zirconia is often used in restorative crowns because of its biocompatibility and smooth surface finish.
Polymers Polymers are molecules with a large number of repeating units of covalently bonded chain of atoms. They are versatile biomaterials with applications on facial, orthopaedic, and dental prosthesis. Example A common polymer used in implants is silicone. Silicone is polymerized siloxanes. It contains silicone-oxygen backbone chain with organic side groups bonded to the silicon atoms.
Silicone has a long polymer chain. The intermolecular forces of attraction between the chains are v ery strong. Therefore, silicone has high strength and durability. Also, its long chains can uncoil and slide past each other, mak ing the material flexible. Because of its strength and flexibility, silicone i s often used to replace original joint surfaces.
Key Points Medical implants are substances or devices used to replace, support or enhance a biological part of the human body. Materials used for medical implants ca n be categorized into three types: metals, ceramics, and polymers. Metals for implants can be pure or alloys (combinations of one or more metals). They are held together by metallic bonds. Ceramics are made up of inorganic and nonmetallic atoms held together by ionic or covalent bonds. Polymers are molecules with a large number of repeating units of covalently bonded chain of atoms. THE USES OF DIFFERENT MATERIALS ACCORDING TO THEIR PROPERTIES AND STRUCTURES: SPORTS EQUIPMENTS
At the end of the lesson, you should be able to relate the properties and structures of sports equipment to their function. In this lesson, you will learn about the different materials used in making sports equipment.
How are the basic structures of sports equipment related to their properties and uses? Sports equipment is any necessary item that is used to play sports, can be a game equipment (ball, racket, net) or a player's equipment (shoes, pads, clothes).
Materials Used for Sports Equipment In the field of sports, material selection is very important for the success and performance of any athlete. The characteristics of the materials should include strength and durability for each sports equipment to perform its purpose well. In general, the materials used in mak ing sports equipment are also the same with the materials in making medical implants. It ca n also be categorized into three types: metals, ceramics, and polymers. However, some of the materials also are made of natural materials like wood.
Metals Metals are composed of particles held together by strong metallic bonds, making them strong and durable. Examples Alloys are usually used in sports equipment that requires strength or stiffness in weight performance. They are made of two or more metals and other substances which improve the strength, hardness, durability, formability, a nd tensile strength of the metal. For example, aluminum alloy is one of the most common alloys used in the frameset of a bicycle. This material does not only support the weight of the person but also provide a lightweight feel without sacrificing its durability. Stainless steel is commonly used in making golf clubs. Titanium alloys are used in making baseball bats over wood because some players tend to break the bats after hitting the baseball.
Ceramics Ceramics are nonmetallic, inorganic solids with ionic or covalent bonds. They are commonly used in sports equipment parts that receive impact. They are lightweight, durable, and has wear resistance than many plastic materials. Example Ceramic fibers are not traditionally used in sports equipment. However, with the advancement and innovation of manufacturers, they have developed sports equipment and parts which contain ceramics. For example, carbon-ceramic rotors are used in race car brakes. The ceramics used together with carbon makes the car breaks lightweight as well as durable. Ceramic fibers are also used in several head tennis racquets which add power whenever hitting the ball.
Polymers Polymers have molecules with a la rge number of repeating units of covalently bonded chain of atoms. They are used to make protective sports equipment. They are known for durability and f lexibility. Example Polycarbonate is a strong, shatter-free polymer that is usually found in protective sports equipment such as in biking and equestrian competitions. They can be also seen in protective visors a nd sunglasses as well as swimming goggles. Polyurethane is commonly used in soccer balls. I t is a synthetic material that coats the leather material in the ball and protects it from damages like tears, scuffs, and scratches.
Key Points Sports equipment is any necessary item that is used to play sports, can be a game equipment (ball, racket, net) or a player's equipment (shoes, pads, clothes). In general, the materials used in making sports equipment are also the same with the materials in making medical implants. It can also be categorized into three types: metals, ceramics, a nd polymers. Metals are composed of particles held together by strong metallic bonds, making them strong and durable. Ceramics are nonmetallic, inorganic solids held together by ionic or covalent bonds which make them lightweight, durable, and has wear resistance than many plastic materials. Polymers are molecules with a large number of repeating units of covalently bonded chain of atoms which are usually used in making protective sports equipment .
THE USES OF DIFFERENT MATERIALS ACCORDING TO THEIR PROPERTIES AND STRUCTURES: ELECTRONIC DEVICES
At the end of the lesson, you should be able to relate the properties and structures of electronic devices to their uses. In the age of technology, almost everyone owns a device that has electronic devices, such as capacitors, inductors, and resistors.
Have you ever wondered what materials make up the electronic devices? Electronic devices are components for controlling the flow of electrons or electricity. Common examples include capacitors, inductors, and resistors. They are often small and combined into packages called integrated circuits .
Capacitors A capacitor stores electrical energy temporarily in an electric field. It has two electrical plates separated by a dielectric. The dielectric is an insulator that stores energy when polarized. The electrical plates are made of conductive materials, such as metals and electrolytes. On the other hand, the nonconducting dielectrics are often made of ceramic, plastic film, and glass.
Example Film capacitors are the most common type of capacitors. Their dielectrics are made of plastic films, such as polystyrene. Polystyrene, a synthetic polymer made from the monomer styrene, has no free flowing electrons, so i t has superior insulating properties. On the other hand, metals like aluminum are used as electrical plates in film capacitors. Metals have free flowing electrons, so they are good conductors of electricity. Long thin strips of the metal foil with the dielectric material are sandwiched together and then wound into a tight roll.
Inductors An inductor resists changes in electric current passing through it. It is often comprised of conductors wound into a magnetic core. When an electric current passes through its coil, it produces a magnetic field, which in turn produces electric current. In other words, an inductor stores energy on the basis of reactive magnetic flux .
Example A typical inductor has copper wires, which a re good electrical conductors, wound around a magnetic iron or ferrite core. Ferrites are ceramic materials comprised of iron oxides combined with nickel, zinc, or manganese compounds. They have high magnetic permeability and high electrical resistivity.
Resistors A resistor reduces the amount of current and lowers the voltage levels within circuits. The reduction in current or voltage results in the transformation of electrical energy into heat. A resistor is necessary in devices that need circuit adjustments, such a s those that need control of volume or dimming of light.
Example The most common type of resistor is the carbon resistors, which are cheap general purpose resistors. They are mainly composed of a mixture of conducting graphite or carbon powder and a nonconducting ceramic powder.
The resistive value of the resistor depends on the ratio of graphite to ceramic (conductor to insulator). If the amount of carbon is higher, then the overall resistance is lower. The mixture is then placed in an insulating material with metal wires connected to each end.
Key Points Electronic devices are components for controlling the flow of electrons or electricity. A capacitor stores electrical energy temporarily in an electric field. It has two electrical pl ates separated by a dielectric. The dielec tric is an insulator that stores energy when polarized. An inductor resists changes in electric current passing through it. It is often comprised of conductors wound into a magnetic core. A resistor reduces the amount of current and lowers the voltage levels within circuits. It is often c omprised of a mixture of conductors and insulators. THE USES OF DIFFERENT MATERIALS ACCORDING TO THEIR PROPERTIES AND STRUCTURES: CONSTRUCTION SUPPLIES
At the end of the lesson, you should be able to relate the properties and structures of construction materials to their uses. In the previous lessons, you have learned about the uses of metals, ceramics, and polymers in medical implants, sports equipment, and electronic devices. In this lesson, you will learn about the uses of these materials in construction supplies.
What are the properties of materials considered in designing and building homes, schools, and other infrastructures? Materials Used for Construction Supplies In general, the materials used for construction supplies can be categorized into three, namely, metals, ceramics, and polymers. Metals Metals are strong and durable construction materials because of the strong metallic bonding between metal atoms. They have a wide range of applications in construction, including roofing, drainage components, and handrails. As the structural framework of buildings, metals should be durable and corrosion resistant. Corrosion, the process by which something deteriorates because of oxidation, is a major factor in assessing the longevity of the metallic material. Example Steel is one of the oldest k nown construction material. It is an a lloy composed primarily of iron and carbon. It is widely used in construction because of its high tensile strength and low cost. When chromium is added to steel, the alloy is referred to as stainless steel. The addition of about 10.5 to 30% chromium gives rise to superior corrosion- and stain-resistant properties. Steel forms iron oxide (rust) in the presence of oxygen. In comparison, stainless steel does not form rust. Instead, it spont aneously forms a chromium oxide layer on its surface on contact with oxygen. This passive layer is impermeable and has the ability to repair itself
Ceramics Ceramics are inorganic, nonmetallic materials comprised of metal, nonmetal, or semimetal atoms held together by ionic or covalent bonds. These materials are often used in the construction industry. They a re used as abrasive, flooring, roofing and wall tiles, and countertops. Example Silicon carbide (SC) is a compound of silicon and carbon. It is a nonmetallic ceramic material that behaves almost like a diamond. It is the lightest and the hardest ceramic material. It has high tear resistance. It is also highly resistant to strong acids and b ases. SC is a construction supply and is often used as an abrasive because of its high tear resistance and durability. Anabrasive is a material that finishes a workpiece through rubbing. For instance, SC is used in stripping and finishing flooring materials, such as wood.
Polymers Polymers are large molecules with repeating units called monomers. They ha ve a wide range of applications in construction including flooring, windows pipes, insulation, and signage. For instance, plastics, which ar e synthetic polymers that can be molded or extruded into different shapes, are used as the replacement for glass and metal pipes. Example Polymethylmethacrylate or acrylic is a synthetic polymer of methyl methacrylate.
Acrylic has high molecular weight and strong London dispersion forces. It is a shatterproof and transparent plastic. Hence, i t is used as a replacement for glass. Like glass, acrylic can be molded into different shapes. Granules of acrylic are poured into a machine that heats them up. As the temperature of the polymer is increased, intermolecular forces are disrupted turning the polymer i nto a viscous liquid. At high temperatures, it can be placed in molds and upon cooling, it solidifies having the shape of its container.
Key Points Metals, which are materials held together by strong metallic bonds, are used as roofing, drainage components, and handrails. Ceramics, which are inorganic, nonmetallic materials held together by ionic or covalent bonds, are of ten used in the construction industry as abrasive, flooring, roofing and wall tiles, and countertops. Polymers, which are large molecules with repeating units, have a wide range of applications in construction including flooring, windows pipes, insulation, and signage.
THE USES OF DIFFERENT MATERIALS ACCORDING TO THEIR PROPERTIES AND STRUCTURES: HOUSEHOLD GADGETS
At the end of the lesson, y ou should be able to relate the properties and structures of ho usehold gadgets to their uses.
Household appliances or gadgets are electrical and/or mechanical machines which can (1) accomplish some household functions such as cooking; (2) make the living space more comfortable by cooling the surroundings; or (3) provide entertainment.
What are the materials used in making household appliances? How are the properties of these materials determine their uses? Cooking Appliances Cooking appliances are used to heat food ingredients during the cooking process. Examples include toaster, oven, boiler, coffee maker, hot plate, and rice cooker. Most of the cooking appliances are powered by electricity. Hence, they are mostly ma de of electrical conductors such as steel, aluminum, and copper. To protect the users from electric shock, their handles a re often made of polymers for electrical insulation. Example An oven toaster is an a ppliance that uses electricity to heat and toast bread. An important part of the toaster is the heating element.
The heating element is often made of nichrome wire, which is an alloy of nickel and chromium. It converts electricity into heat through a process called resistive heating. Electric current passes through the element and encounters resistance. Because of the resistance, the electrical energy is converted into heat. Nichrome is an ideal material for heating element because of its hi gh resistance. It also forms a thin layer of chromium oxide when it is heated for the first time. This layer protects the nichrome from breaking or burning out. Cooling Appliances Cooling appliances are used to lower the temperature and circulate the air in a room. They are often used during hot we ather to make the living space more comfortable. Electric fans and air conditioners are examples of cooling appliances. They are powered by electricity so many of their components are made of metals. Their covers are often made of polymers or plastics. Example An electric fan is an appliance that uses rotating blades (or paddles) to circulate air. Unlike an air conditioner, a fan does not cool air. However, it produces a cooling effect by moving the air around the room. The moving air or breeze allows your skin to evaporate sweat faster, cooling your skin. An important part of an electric fan is the motor, which converts electric energy into mechanical energy, often through an interaction of magnetic fields and current-carrying conductors. Copper is a metal commonly used in coil windings, bearings, and connectors of motors because of its high electrical conductivity (due to its free flowing electrons), high electrical efficiency, and low cost.
The motor is then attached to the fan blades through a shaft. The blades are often made of wood, iron, aluminum, or plastic. It is important for the blades to be light, durable, tough, and easily molded or cut into shapes. Home Electronics Consumer electronics or home electronics are equipment intended for everyday use. They are often used for entertainment. They include television, DVD players, video recorders, and video game consoles. They have software embedded within the hardware of electronic components. Example Most home electronics have electronic panel displays. A typical example of material used in display is the liquid-crystal display (LCD). LCD is made up of liquid crystal, a state of matter between solid and liquid. A liquid crystal may flow like a liquid, but its molecules are oriented in a crystal-like manner.
If you look closely on an LCD TV screen, you will notice that the images are made of millions of tiny blocks called pixels (picture elements). Each pixel can be switched on or off very rapidly to make the images move. These pixels are controlled electronically using liquid crystals. Select one household appliance that you often use at home or in school. Research how it was invented and how it works. Also, find out what materials are used to build it. Then design a future version of that appliance. What do you think? Why is it necessary to continue the research on materials that can be used for the manufacturing of household devices?
Key Points Household appliances or gadgets are electrical and/or mechanical machines which can (1) accomplish some household functions such as cooking; (2) make the living space more comfortable by cooling the surroundings; and/or (3) provide entertainment. Many appliances are powered by electricity so they are mostly made of electrical conductors such as metals and alloys. Polymers are used in covers and handles as electrical insulation. Most home electronics have electronic panel displays made up of liquid crystals, a state of matter between solid and liquid. THE STRUCTURES, PROPERTIES, AND FUNCTIONS OF BIOMOLECULES
At the end of the lesson, you should be able to explain how the structures of biological macromolecules such as proteins, carbohydrates, lipids, and nucleic acids determine their properties and functions.
Biomolecules are large organic co mpounds that are important to life’s processes, such a s respiration and metabolism. There are numerous biomolecules with different structures and functions. They are generally classified into four major groups – proteins, carbohydrates, lipids, and nucleic acids. In this lesson, you will look into the general structure, properties, and functions of each of these groups of biomolecules.
Proteins Proteins are biomolecules composed of amino acid units. Amino acids are organic molecules that have a central carbon atom bonded to four different groups — an amino group ( −NH2), an acidic carboxyl group ( −COOH), a hydrogen atom, and a variable side chain, R. The side chain can range from a single hydrogen atom to complex ring structures.
In a protein, the amino acids are linked via a peptide bond. This peptide bond is formed between an amino group of one amino acid and an acid carboxyl group of another amino acid. A chain of two or more amino acids linked together by peptide bonds is called a peptide.
The smallest protein has about 50 amino acids. However, large proteins can have as many as 1000 amino acids, arranged in any possible sequence. It is estimated that human cells can create between 80 000 to 100 00 0 different proteins. The shape of a protein is important so that it can carry out its function. Long chains of amino acids fold into a unique threedimensional shape. Some areas of the protein may twirl into helices, like the coils of a telephone cord. Other areas may be repeatedly bent into a pleated sheet, like the folds of an accordion. An important intermolecular force of attraction that dictate and maintain the shape of a protein is the hydrogen bonding.
Properties Proteins can participate in neutral, acidic, or basic reactions because their amino acids have an acidic carboxyl end and a basic amino end. The amino acids are amphoteric which means they can function either as an acid or a base. Also, proteins have high molecular weights because they are comprised of many amino acids.
Functions The sequence of amino acids determines the protein’s shape and function. Proteins play many important roles in living cells. T hey can hasten chemical reactions, transport substances, and provide structural support. Many proteins function as enzymes, which are molecules that cataly ze or speed up chemical reactions in the body . The reactant molecules bind to the active site of the enzymes, where they react to form products. Enzymes have shapes that are highly specific for their functions. A slight change to th eir structures will inhibit them to do their function.
Transport proteins carry small particles throughout the body. For example, the protein haemoglobin carries oxygen in the blood from the lungs to the rest of t he body. An important part of hemoglobin is its iron group (called heme), the part to which oxygen binds.
Structural proteins are fibrous proteins which have long, thin structures. A typical example of a structural protein i s keratin, which is a component of the protective covering of most animals – hair, nails, skin or feathers.
Carbohydrates Carbohydrates are molecules that are composed of carb on, hydrogen, and oxygen. They have a general formula of CnH2nOn. They can be grouped depending on the number of their monomer units call ed saccharides. Carbohydrates can be divided into three major groups: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides are the simplest form of carbohydrates. They contain either five or six carbon atoms. They have open-chain and cyclic forms. A typical example of monosaccharide is glucose, C6H12O6, one of the products of photosynthesis in plants.
Disaccharides Disaccharides are two monosaccharides bonded to each other. The monosaccharides are linked through an ether (C−O−C) group. A common example of a disaccharide is the sweetener sucrose, or table sugar. Sucrose is formed by glucose and fructose.
Polysaccharides are long chains of monosaccharide units. They are also called complex carbohydrates . Similar to disaccharides, the monosaccharides in a polysaccharide are linked through an ether bond. An example of a polysaccharide is starch, which is used to store energy in plants. I t is comprised solely of glucose subunits.
Properties Monosaccharides and disaccharides are small molecules with multiple polar groups so they are water soluble. Because they exhibit hydrogen bonding in their structures, they have high melting points. In comparison, polysaccharides are less soluble due to their large sizes a nd complex shapes. For example, starch and glycogen are both insoluble in water. On the other hand, cellulose, also water-insoluble, cannot be digested by humans because the appropriate enzyme to breakdown cellulose into simpler monosaccharides is lacking. Hence, nutritionists call c ellulose as dietary fiber because it just passes through the digestive system unchanged.
Functions The main function of carbohydrates is to store and provide energy . They are broken down into smaller glucose units that can be easily absorbed by the cells. When glucose is further broken down, the energy released by breaking its chemical bonds are used or stored by the body in the form of glycogen. Some carbohydrates also serve as the framework of cellular structures . For example, cellulose makes up the cell wall of plant cells. Chitin, another carbohydrate, forms the exoskeleton of arthropods and the cell wall of fungal cells.
Lipids Lipids are large, nonpolar biomolecules. They are mainly c omposed of carbon, hydrogen, and oxygen. Unlike proteins and carbohydrates, lipids are not polymers with repeating monomer subunits. They have many kinds including triglycerides, waxes, and steroids.
Triglycerides Triglycerides are lipids composed of glycerol and fatty acids. Glycerol is a molecule with three carbons, each containing a hydroxyl (−OH) group while fatty acid is a long chain of carboxylic acid.
When three fatty acids bond to glycerol, they form ester bonds.
Triglycerides can be solid or liquid at room temperature. If solid at room temperature, they are called fats. Fats, such as lard and butter, are produced by animals. If liquid a t room temperature, they are called oils. Oils, such as coconut and olive oils, are produced by plants.
Waxes Waxes are lipids that are composed of a fatty acid with a long chain of alcohol. They are produced by both plants and animals. Plants often produce wax that coats their lea ves which prevents them from drying out. Animals such a s bees also produce wax. Bees create their honeycomb structures from beeswax.
Steroids Steroids are lipids without fatty acid chains. Instead, they have multiple rings in their structures. They are built from the basic fourring steroid structure.
An example of a steroid is dietary lipid cholesterol. Cholesterol is the precursor of hormones such as estrogen and progesterone. Recall that hormones are molecules that communicate between organs to regulate physiology and behavior.
Properties Lipids such as triglycerides and waxes are mostly made of nonpolar hydrocarbon chains, making them generally insoluble in wa ter. The hydrocarbon chains are the “hydrophobic (water -fearing) tails” of lipids. On the oth er hand, their hydroxyl, ester, and ether groups can interact with water. These groups are called “hydrophilic (water -loving) heads.” When lipids are mixed with w ater, they arrange themselves in a spherical form called a micelle.
Functions Lipids are the reserved sources of energy . The energy stored in their bonds is used by the body for fuel. When the energy is abundant, cells store the excess energy in the fatty acids of triglycerides. Lipids like waxes are used as a protective coating of organisms. Because they are hy drophobic, lipids protect plants and animals from drying out by controlling evaporation.
Nucleic Acids Nucleic acids , discovered by Friedrich Miescher in 1869, are biomolecules that are made up of repeating units of nucleotides. Nucleotides are monomers with three components, a 5-carbon sugar, a phosphate group, and a nitrogenous base. The nucleotides are linked through phosphodiester bonds .
If the sugar is ribose, then the nucleotides make up the ribonucleic acid (RNA). On the other hand, if the sugar is deoxyribose, then the nucleotides make up the deoxyribonucleic acid (DNA). Both DNA and RNA have nitrogenous bases. The five common nitrogenous bases are adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).
Properties DNA and RNA are very stable molecules because of the stacking interaction between their hydrophobic parts. Also, hydrogen bonding present between the polar parts of the molecule plays a role in maintaining the structure of the nucleic acid.
Functions DNA contains the genetic instructions for the development and functioning of organisms. This genetic information is converted by the RNA into amino acid sequences of proteins. RNA has three types, messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). The mRNA carries the genetic sequence information between the DNA a nd ribosomes. In ribosomes, proteins are synthesized. The rRNA catalyzes the peptide bond formation while the tRNA serve as the carrier molecules of the amino acids that make up the protein. How are nucleic acids related to proteins? What will happen to the protein being synthesized in the ribosomes if an error occurs in the genetic information passed from the DNA to the RNA?
Key Points Biomolecules are large organic compounds that are important to life’s processes. They are generally classified into f our major groups – proteins, carbohydrates, lipids, and nucleic acids. Proteins are biom olecules composed of amino acid units. The sequence of amino acids determines the protein’s shape and function. In the human body, proteins hasten chemical reactions, transport substances, and provide structural support. Carbohydrates are molecules that are composed of carbon, hydrogen, and oxygen. They have a general formula of CnH2nOn. Their functions are to store energy and serve as the framework of cellular structures. Lipids are large, nonpolar biomolecules mainly composed of ca rbon, hydrogen, and oxygen. They function as reserved sources of energy and protective coating of organisms. Nucleic acids are biomolecules that are made up of repeating units of nucleotides, which are made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base. They encode, transmit, a nd express genetic information.
THE COLLISION THEORY AND FACTORS AFFECTING THE RATE OF A CHEMICAL REACTION
At the end of the lesson, you should be able to explain the collision theory and describe the factors affecting the rate of reaction such as concentration, temperature, and particle size.
Chemical kinetics is the branch of chemistry that studies reaction rates and factors affecting rates. Chemical reactions happen when the reactants collide. But will all collisions result in a reaction or are there requirements for a reaction to occur after collision? According to the collision theory, the rate of a chemical reaction is directly proportional to the number of collisions between the reactants. However, only those which collide effectively will result in a chemical reaction. For an effective collision to happen, the following conditions should be met by the reactants: They must be properly oriented when they collide. They must be energetic enough to surpass the activation e nergy or the energy barrier. Proper Orientation Consider the reaction 2CO+O2→2CO2 which has an activation energy of 277kJmol. Above are the structures of CO and O2 (grey = C, red = O), and below are three possible ways the molecules can collide with one another:
Among the collisions (A, B, and C), only B is expected to proceed in a reaction because it is the one which is properly oriented. This is based on the fact that this collision is expected to form a bond between the C atom of CO and O atom of O2 which is what is seen from the structure of CO2 (shown below).
Because the molecules are not properly oriented in Collisions A a nd C, they will not lead to the formation of the product.
Energy Higher than Activation Energy The activation energy or the energy barrier is the energy needed to be surpassed by the reactants for a reaction to occur. When the energy barrier is higher, the reaction is slower. It should be noted that not all properly oriented collisions have enough energy to result in the transfo rmation of the reactants. The kinetic energy of the reactants should be high enough to exceed the activation energy. Therefore, for CO to react with O2, the kinetic energy of the reactants should be greater than 277kJmol.
Factors Affecting the Rate of Reaction The three factors that can affect the rate of a chemical reaction are concentration of reactants, temperature, and particle size.
Concentration An increase in concentration increases the rate of reaction. Reason: Concentration is the number of molecules present in a specified volume. When the concentration is high, more particles are present; therefore, there is a higher frequency of effective collisions.
Temperature An increase in temperature increases the rate of reaction. Reason: Energy is applied to increase the temperature. The added energy provides additional kinetic energy to the reactant molecules. Higher kinetic energies means greater frequency of effective collisions.
Particle size The smaller the particle, the faster the rate of reaction. Reason: Smaller particles have larger surface area. The greater the surface area, the more sites of collision there will be. Determine which condition (A or B) will make the reaction go faster.
Try it! Solution
Another factor that increases reaction rate is the presence of a catalyst. A catalyst is a chemical species that participates in the reaction but does not get used up. How does a catalyst speed up the reaction?
Key Points According to the collision theory, the rate of reaction is directly proportional to the number of collisions between the reactants. An effective collision is characterized by reactants colliding with proper orientation and enough energy to surpass the activation energy. The activation energy or energy barrier is the energy needed to be surpassed by the reactants so that they will be transformed into products. There are three factors that affect the rate of the reaction: 1) concentration, 2) temperature, and 3)particle size. Increasing the concentration or the temperature of the reaction leads to an increase in reaction rate. On the other hand, decreasing the particle size increases the reaction rate.
CATALYSTS: HOW REACTION RATE IS AFFECTED
At the end of the lesson, you should be able to define catalyst and describe how it affects the reaction rate.
Reaction rate is the change in the concentration of reactant or product per unit of time. In the previous lesson, you have learned that the concentration of reactants, temperature, and particle size are f actors affecting t he reaction rate. In this lesson, you will learn about the catalyst, which is another factor affecting the rate of a chemical reaction.
What is a catalyst? How does it affect reaction rates? A catalyst is a substance that increases the reaction rate without being consumed by the reaction. It provides a new pathway for the reaction, one which has a lower acti vation energy. Consider the points A and B separated by a cliff.
The way to get from points A to B is to go around the cliff following the red path. It would take a lot of time and energy to reach point B.
What happens when a bridge is built between points A and B?
The path from Point A to B is shorter so it would take less time to reach point B. In addition, there is less energy required to reach point B. Similarly, in chemical reactions, reactants (A) are combined to form products (B).
A→B For uncatalyzed reactions (red path), the time it takes for the reaction to be completed is relatively longer. However, for catalyzed reactions, the catalysts (bridge) speed up the reaction by providing an alternate path with less required energy for reactants to turn into products.
Mechanism of Catalysis A catalyzed reaction often involves a series of steps. Bonding – The catalyst forms a bond with the reacting molecules. Reaction – The reacting molecules combine or rearrange to form the product. Separation – The product separates from the catalyst. After separation, the catalyst is free again to form a bond with other reacting molecules. .
Energy Diagram of a Catalyzed Reaction Energy Diagram of a Catalyzed Reaction Below is the energy diagram for a chemical reaction. The red line represents the uncatalyzed reaction while the blue one is the catalyzed reaction. Notice that the energies of the r eactants and the products are the same for both catalyzed and uncatalyzed reactions. What is the difference between a catalyzed and an uncatalyzed reaction? The catalyzed reaction has lower activation energy or energy barrier. When there is less ene rgy required for a reaction to proceed, then the reacting molecules will form the products in less time.
Types of Catalysts A catalyst can be homogeneous or heterogeneous. A homogeneous catalyst exists in the same phase as the reaction it catalyzes. It is often in gas or liquid phase. For example, the decomposition of ozone in the atmosphere is catalyzed by chlorine atoms.
Cl+O3→ClO3 ClO3→ClO+O2 ClO+O→Cl+O2 Overall reaction: O3+O→O2 The chlorine atom is a catalyst that is regenerated at the end of the reaction. A heterogeneous catalyst exists in a different phase as t he reaction it catalyzes. It often involves gaseous reactant molecules being adsorbed on a solid catalyst surface. For example, gaseous ethylene is hydrogenated to form ethane in the presence of a palladium catalyst.
Enzymes Enzymes are homogeneous, highly specific, and efficient biological catalysts. They speed up biological reactions even a t relatively low temperatures within the body. They have a shape- specific active site that forms bonds with the reacting molecules called substrates. The substrates react and form the product, which then detaches from the catalyst.
An example of an enzyme is sucrase, which catalyzes the hydrolysis of sucrose to glucose and fructose. The first step of the catalysis is the binding between the enzyme sucrase and the substrate sucrose. In the second step, the presence of water hydrolyzes or breaks sucrose into glucose and fructose. The third step involves the release of the products. In the fourth step, the active site of the sucrase is available for another molecule of sucrose. .
Some reactions are reversible, meaning that a reactant A, can be converted into product B. In the reverse reaction, B is the reactant that can be turned into a product A. A↔B What will be the effect of adding a catalyst for this reaction? Will it increase the rate of the forward reaction? How about for the reverse reaction?
Key Points A catalyst is a substance that increases the reaction rate without being consumed by the reaction. A catalyst increases the rate of the reaction by lowering the activation energy of a reaction. A homogeneous catalyst exists in the same phase as the reaction it catalyzes. A heterogeneous catalyst exists in a different phase as the reaction it cataly zes. Enzymes are homogeneous, highly specific, and efficient biological catalysts.
CALCULATING THE AMOUNT OF REACTANTS AND PRODUCTS IN A CHEMICAL REACTION
At the end of the lesson, you should be able to calculate the amount of reactants and products in a chemical reaction.
Stoichiometry is the study of the quantitative relationships between the amounts of r eactants used and amounts of products formed in a chemical reaction. Consider the formation of water from the reaction between H2 and O2.
2H2+O2→2H2O How many moles of water can be formed from two moles of hydrogen gas? Mole Ratios The coefficients in a balanced chemical equation indicate the relationships between the moles of reactants and products. They are used to express the mole ratios. Mole ratios are ratios between the moles of any two substances in a balanced chemical equation. For example, water forms from molecular hydrogen and oxygen as presented by the equation below.
2H2+O2→2H2O What mole ratios can be written for this reaction? Two moles of hydrogen react with one mole of oxygen.
2molesH21moleO2 Two moles of hydrogen produce two moles of water.
2molesH22molesH2O One mole of oxygen produces two moles of water.
1moleO22molesH2O You can then use the knowledge about mole ratios to calculate the amounts of reactants or products in a chemical reaction. Mole-to-Mole Stoichiometry Suppose you know the number of moles of reactants. You then want to know how many moles of products will be formed in the reaction. Sample Problem: If 1 mole H2 is used up in the reaction, how many moles of H2O will be formed?
How to Do To solve the problem: Step 1: Determine the mole ratio between H2 and H2O. 2molesH22molesH2O Step 2: Assign a variable to the unknown. Let x= moles of H2O formed from 1 mole H2. Step 3: Set up the proportion. 2molesH22molesH2O=1moleH2x Step 4: Rearrange the equation to get an expression to solve for x. x=(2molesH2O)(1moleH2)(2molesH2) Step 5: Solve for x. Solving for x, you get 1 mole H2O. This means that you will produce 1 mole H2O if you have 1 mole H2. x=1moleH2O Mass-to-Mass Stoichiometry In laboratory experiments, you do not measure the moles of the reactants. Instead, you measure their masses. But how do you convert number of moles into mass? In converting mass to moles, or vice-versa, you can use the equation below. moles=massmolarmas Given the mass of one reactant, you can calculate the required mass of the other reactant. Sample Problem 2: How many grams of O2 is needed to react with 1.00 g H2? How to Do The solution to this problem is similar to the previous one, but additional steps are needed. Step 1: Determine the mole ratio between H2 and O2. 2molesH21moleO2 Step 2: Convert the given mass of H2 to moles H2. molesH2=massofH2molarmassofH2 molesH2=1.00gH22.016g/mol molesH2=0.496mol Step 3: Assign a variable to the unknown. Let x= moles of O2 that reacts with 0.496 mole H2. Step 4: Set up the proportion. 2molesH21moleO2=0.496molesH2x Step 5: Rearrange the equation to get an expression to solve for x. x=0.496molesH2(1molesO2)(2molesH2) Step 6: Solve for x. Solving for x, you get 0.248 mole O2. x=0.248mol Step 7: Convert the calculated moles O2 to mass O2. massofO2=(molesO2)(molarmassO2) massofO2=(0.248mol)(32gmol) massofO2=7.94g Therefore, you need 7.94 g O2 to react with 1.00 g H2. Ammonia is produced from the reaction between nitrogen and hydrogen. N2+3H2→2NH3 How many grams of N2 and H2 is needed to produce 10.0 g NH3? Use the following molar masses: N2=28gmol, NH3=17gmol, and H2=2gmol. Try it! Solution Step 1: Determine the mole ratio between the reactants and the product. 3molesH22molesNH3 1moleN22molesNH3 These ratios are based on the balanced chemical equation. Step 2: Convert the given mass of product to moles. molesNH3=massofNH3molarmassofNH3 molesNH3=10.0gNH317g/mol molesNH3=0.588molNH3 Step 3: Assign variables to the unknown q uantities. You may use more than one variable. Let x= moles H2 needed to form 0.588 mole NH3. Let y= moles N2 needed to form 0.588 mole NH3. Step 4: Set up the necessary proportions. 3molesH22molesNH3=x0.588moleNH3 1moleN22molesNH3=y0.588moleNH3 Step 5: Rearrange the equation to get an expression to solve for the variables. x=(3molesH2)(0.588moleNH3)2molesNH3 y=(1moleN2)(0.588moleNH3)2molesNH3 Step 6: Solve the unknowns. x=0.882molH2 y=0.291molN2 Step 7: Convert the calculated moles to grams. massH2=(0.882molH2)(2gmol) massH2=1.76gH2 massN2=(0.291molN2)(28gmol) massN2=8.15gN2
Key Points Stoichiometry is the study of the quantitative relationships between the amounts of reactants used and amounts of products formed in a chemical reaction. Mole ratios are ratios between the moles of any two substances in a balanced chemical equation. You can then use the knowledge about mole ratios to calculate the amounts of re actants or products in a chemical reaction.
CALCULATING THE PERCENT YIELD IN A CHEMICAL REACTION
At the end of the lesson, you should be able to calculate the percent yield (% yield) of a reaction. Imagine that you have 100 chances to shoot a ball inside the ring. Theoretically, you can make all the 100 shots. However, in actuality, you may not make all them. There would be a difference between your theoretical and actual outcomes. In chemical reactions, there are also theoretical and actual outcomes. In this lesson, you will learn that there is a theoretical amount of product that will be formed in a reaction. However, it is often diff erent from the actual amount that y ou get from your experiment.
How can you express the difference between theoretical and actual product yields? In the previous lesson, you have calculated the amount of product that will be formed from a given amount of reactant. This amount of product is the theoretical yield of the reaction. The theoretical yield is the maximum amount of product that can be formed from a given amount of reactant. Consider the reaction below. 2NaOH+H2SO4→Na2SO4+2H2O What is the theoretical yield (in grams) of Na2SO4 that will be formed when 4 moles of NaOH is used in the reaction? How to Do Step 1: Determine the mole ratio between NaOH and Na2SO4. 2molesNaOH1moleNa2SO4 Step 2: Assign a variable to the unknown. Let x= moles of Na2SO4 formed from 4 moles of NaOH. Step 3: Set up the proportion. 2molesNaOH1moleNa2SO4=4molesNaOHx Step 4: Rearrange the equation to get an expression to solve for x. x=(4molesNaOH)(1moleNa2SO4)2molesNaOH Step 5: Solve for x. Solving for x, you get 2 moles Na2SO4. This means that the theoretical yield is 2 moles Na2SO4 for every 4 moles NaOH. x=2molesNa2SO4 Step 6: Convert moles to mass. massNa2SO4=(molesNa2SO4)(molarmassNa2SO4) massNa2SO4=(2molNa2SO4)(142gmol) massNa2SO4=284gNa2SO4 Therefore, the theoretical yield is 284 g Na2SO4. Percent Yield In reality, however, reactions are not always 100% successful. This means that the actual amount of products formed from an experiment, or the actual yield, may be lower than the theoretical yield. The actual yield is also called experimental yield . After performing an experiment, you can calculate how efficient your reaction is in producing the desired product. Percent yield is one way of expressing the efficiency of a chemical reaction. It is the ratio of the actual yield to the theoretical yield expressed as percent. percentyield=actualyieldtheoreticalyield×100 In using the formula, it is important that the actual and theoretical yields have the same units (either in moles or mass) so you can cancel their units. Consider again the reaction between sodium hydroxide and sulfuric acid. 2NaOH+H2SO4→Na2SO4+2H2O Suppose you use 40 g NaOH and produced 15 g H2O. What is the % yield of H2O? Use the following molar masses: NaOH=40g/mol and H2O=18g/mol. How can the formula be used? Step 1: Convert the mass of NaOH to moles. molesNaOH=massNaOHmolarmassNaOH molesNaOH=40gNaOH40g/mol molesNaOH=1molNaOH Step 2: Determine the mole ratio between NaOH and H2O. 2molesNaOH2molesH2O=1moleNaOHx Step 3: Assign a variable to the unknown. Let x= moles of H2O formed from 1 mole of NaOH. Step 4: Rearrange the equation to solve for x. x=(1moleNaOH)(2molesH2O)2molesNaOH Step 5: Solve for x. x=1moleH2O Step 6: Convert moles of H2O to mass of H2O. massH2O=(molesH2O)(molarmassH2O) massH2O=(1molH2O)(18gmol) massH2O=18gH2O
Take note that this is the theoretical yield of H2O. Step 7: Take note of the actual yield given in the problem. actualyield=15gH2O Step 8: Use the formula to calculate the % yield H2O from the reaction. percentyield=actualyieldtheoreticalyield×100 percentyield=15g18g×100 percentyield=83% Consider the synthesis of NaCl from Na and Cl2. The reaction is represented by the balanced chemical equation below.
2Na+Cl2→2NaCl When 10.0 g of Cl2 is used, the reaction produced 12.5 grams NaCl. What is the % yield of the reaction? Use the following molar masses: Cl2=70.9g/mol andNaCl=58.5g/mol. You may follow the steps below.
Step 1: Convert mass of reactant to moles. Step 2: Determine the mole ratio between the reactant and the product. Step 3: Let x= moles of product formed from the given mass of reactant. Step 4: Set-up the proportion. Step 5: Rearrange the equation to solve for x. Step 6: Solve for x. Step 7: Convert moles of product to mass. This is your theoretical yield. Step 8: Take note of the actual yield. Step 9: Calculate % yield using the formula. Try it! Solution Step 1: Convert mass of reactant to moles. molesCl2=massCl2molarmassCl2 molesCl2=10.0gCl2molarmassCl2 molesCl2=0.141molCl2 Step 2: Determine the mole ratio between NaCl and Cl2. 1moleCl22molesNaCl Step 3: Assign a variable to the unknown. Let x= moles of NaCl formed from 10.0 g Cl2. Step 4: Set-up the proportion. 1moleCl22molesNaCl=0.141moleCl2x Step 5: Rearrange the equation to solve for x. x=(0.141moleCl2)(2molesNaCl)1moleCl2 Step 6: Solve for x. x=0.282moleNaCl Step 7: Convert moles of product to mass. This is your theoretical yield. massNaCl=(molesNaCl)(molarmassNaCl) massNaCl=(0.282molNaCl)(58.5gmol) massNaCl=16.5gNaCl Step 8: Take note of the actual yield. actualyield=12.5gNaCl Step 9: Calculate % yield using the formula. percentyield=actualyieldtheoreticalyield×100 percentyield=12.5g16.5g×100 percentyield=75.8% Key Points The theoretical yield is the maximum amount of product that can be formed by a chemical reaction from the given amount of reactant. The actual yield, also call ed the experimental yield, is the real amount of product formed from the reaction when the experiment is performed. The ratio of actual yield to theoretical yield multiplied by 100 is the percent yield (% yield). Chemical reactions do not always go into completion (not 100% successful). Therefore, percent yields are usually less than 100%.
CALCULATING THE AMOUNT OF PRODUCTS BY DETERMINING THE LIMITING REACTANT
At the end of the lesson, you should be able to determine the limiting reactant and calculate the amount of product formed in a chemical reaction. Chemical reactions begin when the reactants are combined under the right conditions, such a s correct temperature and pressure. But when do the reactions stop? A chemical reaction stops when one of the reactants is completely used up. In most chemical experiments, the reactants are not in exact ratios specified by the balanced chemical equation. Often, one of the reactants is used in excess, and the reaction is allowed to proceed until one of the reactants is used up. The reactant that is completely used up in a chemical reaction is called limiting reactant. As its name implies, it limits the extent of the reaction, and thereby determines the amount of product that will be formed. On the other hand, the reactant that still remains after the reaction stops is called the excess reactant . As its name implies, it is in excess in the reaction.
How can you identify the limiting reactant and the maximum amount of product that can be formed in a chemical reaction? Consider the reaction below.
K2O+2HCl→2KCl+2H2O If 10.0 g K2O is made to react with 10.0 g HCl, how many grams of H2O will be formed? Use the following molar masses: K2O=94g/mol, HCl=36.5g/mol, and H2O=18g/mol. How to Do Step 1: Convert the mass of both reactants to their corresponding moles. Moles K2O: molesK2O=massK2OmolarmassK2O molesK2O=10.0g94g/mol molesK2O=0.106molK2O Moles HCl: molesHCl=massHClmolarmassHCl molesHCl=10.0g36.5g/mol molesHCl=0.274molHCl Step 2: Calculate the moles of product that can be formed from each reactant. Moles H2O from K2O: molesH2O=(0.106molesK2O)(2molesH2O)(1moleK2O) molesH2O=0.212molesH2O Moles H2O from HCl: molesH2O=(0.274molesHCl)(2molesH2O)(2molesHCl) molesH2O=0.274molesH2O Step 3: Compare the moles of product formed from each reactant. Moles H2O from K2O is less than moles H2O from HCl. Step 4: Tag the reactant that gives a lower amount of product as the limiting reactant. Since moles H2O from K2O is less than moles H2O from HCl, K2O is the limiting reactant. Step 5: Convert the moles of product formed from the limiting reactant to mass. The calculated mass is the maximum amount of product that you can form from the reaction. massH2O=(molesH2O)(molarmassH2O) massH2O=(0.212mol)(18gmol) massH2O=3.82gH2O Try it! Consider the combustion of butane, one of the main components of liquefied petroleum gas (LPG). 2C4H10+13O2→8CO2+10H2O How many grams of CO2 is produced when 100 g C4H10 undergoes combustion with 200 g O2? Use the following molar masses: C4H10=58g/mol, O2=32g/mol, and CO2=44g/mol. You may follow the steps below. Step 1: Convert the mass of each reactant to their corresponding moles. Step 2: Calculate the moles of product that can be formed from each reactant. Step 3: Compare the moles of product formed from each reactant. Step 4: Tag the reactant that gives a lower amount of product as the limiting reactant. Step 5: Convert the moles of product formed from the limiting reactant to mass. Try it! Solution Step 1: Convert the mass of each reactant to their corresponding moles. Moles C4H10 molesC4H10=massC4H10molarmassC4H10 molesC4H10=100g58g/mol molesC4H10=1.72molC4H10 Moles O2 molesO2=massO2molarmassO2 molesO2=200g32g/mol molesO2=6.25molO2 Step 2: Calculate the moles of product that can be formed from each reactant. Moles CO2 from C4H10: molesCO2=(1.72molesC4H10)(8molesCO2)(2molesC4H10) molesCO2=6.88molesCO2 Moles CO2 from O2: molesCO2=(6.25molesO2)(8molesCO2)(13molesO2) molesCO2=3.85molesCO2 Step 3: Compare the moles of product formed from each reactant. Moles CO2 from O2 is less than the moles CO2 from C4H10. Step 4: Tag the reactant that gives a lower amount of product as the limiting reactant. Since moles CO2 from O2 is less than moles CO2 from C4H10, O2 is the limiting reactant. Step 5: Convert the moles of product formed from the limiting reactant to mass. This is maximum amount of product y ou can form from the reaction. massCO2=(molesCO2)(molarmassCO2) massCO2=(3.85mol)(44gmol) massCO2=169g The hydrogenation of benzene is an exothermic process, that is, energy (in kilojoules, kJ) is released when the reaction happens. C6H6+3H2→C6H12+208kJ How much energy (in kJ) is released when 2 moles C6H6 is made to react with 2 moles H 2, and the reaction is only 80% successful?
Key Points The limiting reactant is the reactant that is completely used up in a chemical reaction. It determines the maximum amount of product that can be formed from the reaction. The excess reactant is the reactant that is still present after the reaction stops. CHEMICAL REACTION: ENDOTHERMIC AND EXOTHERMIC
At the end of the lesson, you should be able to explain how chemical reactions are accompanied by energy changes.
Chemistry is defined as the science that studies matter — its properties, changes, and the energy associated with these changes. Have you ever wondered how energy participates in chemical reactions? A chemical reaction occurs when two or more substances react to form new substances or products. It is often acc ompanied by energy changes. It can be classified either a s endothermic or exothermic, depending on the energy changes ( ΔE) it undergoes. ΔE=finalE–initialE Endothermic reactions require energy for it to proceed. This means that the final energy of the reaction is higher compared to its initial energy due to the added energy. Therefore, the ΔE is positive. Reactants+Energy→Products For example, the high-temperature electrolysis of water is an exothermic reaction. This reaction is used to make hydrogen f uel and breathable oxygen.
2H2O+Energy→2H2+O2 On the other hand, exothermic reactions release energy . This means that the final energy of the reaction is lower compared to its initial energy because energy is given off. Therefore, the ΔE is negative . Reactants→Products+Energy Explosions involve exothermic reactions. For example, the decomposition of ammonium nitrite yields water and nitrogen and releases a large amount of heat.
NH4NO2→N2+2H2O+Energy Are the following reactions endothermic or exothermic? Example 1: When H2 combines with O2, an explosion may be observed as H2O is being formed. The balanced chemical equation that represents this reaction is:
2H2+O2→2H2O Where is the energy in the reaction? To answer this, take note that explosion is observed a s H2O is being formed. Explosions occur when energy is released. The reaction is written as:
2H2+O2→2H2O+Energy Because energy is on the product side, the reaction is exothermic.
Example 2: When CaCO3 is heated, it decomposes to CaO and CO2. The balanced chemical equation that represents this reaction is:
CaCO3→CaO+CO2 Where is the energy in the reaction? To answer this, take note that the reaction proceeds when CaCO3 is heated. Heat is a form of energy and it must be applied for the reaction to occur. The reaction is written as:
CaCO3+Energy→CaO+CO2 Because energy is on the reactant side, the reaction is endothermic. Explore! Photosynthesis is the process by which plants produce their food glucose (C6H12O6) along with O2 from CO2 and H2O. Is photosynthesis an endothermic or an exothermic process? To answer this, you should know where the energy is placed in the reaction (either reactant or product side). In what form is the energy involved in photosynthesis? What does the plant do with the energy for photosynthesis to occur? Try it! Matches are lighted by striking the head of the matchstick against the specially prepared pad found along the side of the matchbox. The head of the matchstick contains KClO3 while the strip contains P4. Obtain a matchstick and a matchbox. Strike the head of the matchstick against the pad in the matchbox. Feel the surroundings near the lighted matchstick. Based on your observation, is the reaction between KClO3 and P4 endothermic or exothermic? Explain your answer. Warning: Do not play with matches. Use only one to two matchsticks at a time when doing the activity to avoid causing large fires. Exothermic reactions give off heat. Thus, they are good sources of energy. How do you think are the heat from these reactions harvested to convert them to usable forms of energy (e.g. mechanical, electrical)?
Tip Common misconception is that exothermic reactions are accompanied by increase in energy while endothermic reactions are accompanied by decrease in energy. To avoid this, remember the following: The term exothermic came from the Greek words exo meaning "outside" and therme meaning "heat." So the energy EXits in EXothermic reactions, hence the energy becomes lower. On the other hand, the term endothermic came from the Greek words endo meaning "outside" and therme meaning "heat." So energy ENters in ENdothermic reactions, hence the energy becomes higher.
Key Points Endothermic reactions are accompanied by a n increase in energy because the energy is absorbed (ΔEis positive) by the reactants. Energy is found on the reactant side for an endothermic reaction. Exothermic reactions are accompanied by a decrease in energy because energy is released (ΔE is negative) when products are formed. Energy is found on the product side for an exothermic reaction. ΔE=finalE–initialE HARNESSING ENERGY FROM DIFFERENT SOURCES
At the end of the lesson, you should be able to explain how energy is harnessed from different sources of energy.
Where does the electricity we use every day come from and how are they generated There are several sources of energy that are harnessed to generate the power distributed by our electricity providers. These energy sources include fossil fuels, biogas, geothermal, hydrothermal, batteries, solar cells, a nd biomass.
Fossil fuels and Biogas Fossil fuel is the general term given to combustible products of buried organic matter that decayed under extreme temperature and pressure. Fossil fuels include crude oil (e.g., octanes C8H18), natural gas or biogas ( CH4), and coal ( C). Biogas is a gas produced from anaerobic (absence of oxygen) decomposition of organic matter. How is energy harnessed? The components of fossil fuels are heated and vaporized to steam which drives the turbines and generate electricity.
Geothermal Energy Geothermal energy refers to the heat produced inside the Earth. This energy is harnessed from the molten rocks near volcanic regions.
How is energy harnessed? The molten rocks heat the groundwater to steam which drives the turbines to generate electricity.
Hydrothermal Energy Hydrothermal energy refers to the heat obtained from hot water from hydrothermal vents or seawater in contact with hot rock beds.
How is energy harnessed? Hot water from hydrothermal vents is collected into a heat exchanger. The heat from the water is tran sferred to another fluid (e.g. isobutane) which evaporates and drives the turbines to generate electricity.
Batteries Batteries are also called electrochemical cells . They are devices that store and convert chemical energy into electrical energy. They can be disposable or rechargeable. The energy from b atteries comes from a chemical reaction (e.g. redox reaction between CuSO4 and Zn to form ZnSO4 and Cu).
How is energy harnessed? When a battery is connected to a n external circuit, electrolytes move within the battery, and chemical reactions are completed at the two terminals of the battery. The flow o f electrons in the reactions generate the current (flowing charges) a nd delivers electricity to the external circuit.
Solar Cells Solar cells are devices that can collect light energy from the sun and convert it into electricity. How is energy harnessed? Light energy is collected over solar panels. The collected energy ca n be stored in batteries or can be directly converted to electricity.
Biomass Biomass refers to the organic matter from living organisms a nd often refers to plants or plant -based materials that can be converted to energy. It is the oldest source of energy known to man.
How is energy harnessed? The biomass is burned to generate heat. The heat produced can be directly used to do daily chores such a s cooking. Electricity may also be generated from biomass. The components of biomass are burned in a boiler. The generated heat is used to produce steam which drives the turbines to generate electricity.
Renewable and Nonrenewable Energy Energy sources may be renewable or nonrenewable. Renewable energy sources are those that are naturally replenished. Biogas and biomass are renewable energy sources. Geothermal, hydrothermal, and solar energies can also be considered renewable. In contrast, nonrenewable energy sources are finite, so they will get depleted over time. Crude oil is a nonrenewable energy resource. How about batteries? Disposable batteries are nonrenewable. Rechargeable batteries can be classified as nonrenewable or renewable, depending on the energy source used for recharging (e.g., if solar energy is used to recharge the batteries, then it is renewable).
Electricity from Power Plants Power plants are designed to generate electricity from energy harnessed from different sources. Common among power plants are vapor-driven turbines. The turbines are rotated by the vapor and in turn spin a generator. The spinning generator then produces electricity that is transported by transmission lines to the distributors and to our homes. Research on the following and classify the type of energy source they use to generate electricity. Daniell Cell Malampaya power plant Makiling-Banahaw (Mak-Ban) power plant islaSOL II Sultan Energy Philippines Green Power Bukidnon Phil. Inc.
Key Points Energy is harnessed from the following sources: fossil fuels, biogas, geothermal, hydrothermal, batteries, solar cells, and biomass. Energy sources may be renewable or nonrenewable. Renewable energy sources are those that do not get depleted. Nonrenewable energy sources are finite, so they will get depleted over time. Common structures in all power plants are the steam - or vapour-driven turbines which spin generators to produce electricity. HOUSEHOLD CLEANING PRODUCTS
At the end of the lesson, you should be able to give examples of household cleaning products a nd explain the need to use them .
Cleaning products contain substances that remove dirt, stain, a nd bad smell. There are different cleaning products, and some of them are used to clean surfaces such as bathroom tiles, floors, sinks, and drains. Others are used to clean clothing, blankets, and curtains. Cleaning products include detergent, bleach, air freshener or purifier, and disinfectant. What are the cleaning products you
use at home? Detergent A detergent contains surfactants, which are substances with cleaning properties. Surfactants have long water-insoluble hydrocarbon tail and water-soluble polar heads. When these molecules are placed in water, they form micelles. They orient themselves with the hydrocarbon tails, sticking to one another while the polar heads are pointing outwards and into the water. A mixture of detergent and water is a colloid. Micelles are dispersed throughout the water, so the mixture appears cloudy. When oil or grease is present, the micelle disperses and entraps the grease. When the detergent is rinsed out, the grease comes with i t.
Bleach Bleach is a household cleaning agent used to remove dyes and whiten clothing. The color that stains white fabrics typically arise from organic dyes and pigments. For example, when carrot juice spills on your white garment, the pigment beta -carotene binds with the fabric.
Chlorine-based bleach is used to break the chemical bonds of the pigment. The pigment is changed to a different substance that do not absorb visible light. Hence, the stained garment appears white again. Air freshener or Purifier Air freshener or purifier is used to emit fragrance in different spaces at home, especially in restrooms. It can be in the form of spray, candle, oil, bead, or gel. Its main purpose is to eliminate or mask unpleasant odors. Its name is misleading though becau se it does not really freshen or purify the air. Solid or liquid air fresheners (candle, oil, bead, or gel) have volatile fragrant molecules. These molecules easily change from solid or liquid into gas, even at room temperature. When they mix with air, they move via diffusion.Diffusion is the movement of particles from higher concentration to lower concentration. Hence, the air freshener molecules spread out across the room.
Spray air fresheners are aerosols. Aerosols are colloids of solid or liquid particles in gas. The fragrant molecules dissolve in air. When these molecules are allowed to escape their spray c ontainers, they mix with air, and the fragrant smell spreads. Disinfectant A disinfectant is an antimicrobial household product. It kills microorganisms on surfaces of inanimate objects. Note that it is different from antiseptics, which are used on living things to kill microorganisms. The effectiveness of a disinfectant depends on the number of microorganisms, environment (temperature), time of exposure, and nature of microorganisms. Most disinfectants, such as alcohol a nd chlorine, work by denaturing proteins of microorganisms. When their proteins are dama ged, metabolic processes are disrupted, causing death.
Key Points Cleaning products contain substances that remove dirt, stain, a nd bad smell. They come in different physical forms such as solids, liquids, and aerosol. Cleaning products include detergents, bleaches, deodorizers, and disinfectants. ACTIVE INGREDIENT IN PRODUCT LABELS
At the end of this lesson, you should be able to identify the active ingredient in c ommon household products used for cleaning. The active ingredient is the compound that acts to fulfill the function of a said product. A finished household product is usually a mixture of many different compounds.
How can we identify the active ingredient of a product assuming it is a mixture? All products have an active ingredient that enables it to work. Some products only have one active ingredient while others may have more than one. Here are some important pointers in determining the active ingredient. The active ingredient can be classified as acidic, basic, or neutral. The determination of its acidity or alkalinity often dictates how the product will work. The active ingredient must always be labelled in consumer goods.
Importance of an Active Ingredient Knowing the active ingredient in certain products will tell you what function they can serve. Product labels are required to put down their active ingredients. Some of these ingredients may be toxic to the user or even to the environment. In some cases, a f ew household products will share the same active ingredient, allowing them to be us ed for different purposes. While other produc ts may have the same function, they have different active ingredients. The table below contains different cleaning products with specific active ingredients and their specific functions.
Different active ingredients have different modes of action on how they are able to clean certain materials. The basic idea for most of these ingredients is to convert a “dirt” substance into so mething that is soluble in water. The active ingredient determines the mode of action of a specific product. Dissolution - A common mode of action based on the principle of like-dissolves-like and the concept of solvent – solute interactions. Acid –Base - Certain substances are either acidic or basic. An acid will react with a base, or vice versa, allowing it to be dissolved or carried away by water.
Reduction – Oxidation - Oxidizing agents work to convert certain substances into water-soluble ions. Surfactants - Detergents and soaps can be classified as surfactants. They form tiny vessels known as micelles that carry away the undesired material. Disinfectant - The reagent targets a biological organism responsible for an undesired effect. Example Micelles form from amphiphatic molecules. Amphiphatic molecules are molecules that have polar and non -polar regions in their structure. This amphiphatic nature allows them to form micelles.
The micelles are soluble in water due to the polarity of the head, and the nonpolar tail interacts with oils and greases that allow it to be carried in a vessel that can dissolve in water.
Explore! Product development is an essential part of the industry. A little knowledge in chemistry is a useful skill in finding alternative products because active ingredients may share similar properties. These ingredients can be found in everyday materials. Homemade cleaning materials using similar ingredients can be made from common items such as vinegar, citrus f ruits (lemons and calamansi), and baking soda. Can you give examples of how baking soda (sodium carbonate, basic properties) or vinegar (acetic acid, acidic properties) can be used as substitute cleaning products? Try it! Given the different modes of action of specific active ingredients, list down as many possible chemical reagents you can find in your house that may fit under these modes of actions. Key Points Active ingredient is the reactive and functional ingredient of a household product. An active ingredient may have several mechanisms where it can remove stains, ranging from acid-base, oxidation – reduction, disinfectants, surfactants, and dissolution (via solvent – solute interaction). Two different products can have similar modes of action as long as their active ingredients have similar properties.
OTHER USES OF INGREDIENTS IN CLEANING AGENTS
At the end of the lesson, you should be able to identify the commo n ingredients (other than active ingredient) in cleaning agents and their uses. Active ingredients are only a part of the entire mixture that we call the product or in this case, the cleaning agent. For all cases of practicality, the product cannot be sold as a pure active ingredient for commercial a nd practical reasons. Other components of the mixture have specific purposes in making the cleaning a gent. A cleaning agent is a mixture of many compounds. They are considered as additive ingredients . These additive ing redients have some functions in the product. Some ingredients are added to mixtures while others have more complex mechanisms. Some functions if additive ingredients include: solvents, fragrance enhancers, masking ag ents, builders, preservatives, antimicrobial agents, and bubble enhancers.
Solvents A solvent is often used to increase the quantity of the cleaning agent. The solvent is used to dilute the cleaning agent to its minimum functional concentration. For instance, ethanol which is used as a disinfectant is functional at 40% solution while bleach can be functional as low as 5% solution.
Fragrance enhancers In other cases, fragrance enhancers are added to products to mask a more putrid smell. Pa rticularly, bathroom cleaners use these added fragrances. Fragrances often come in the form of essential oils.
Masking agents A scent of a product is often underestimated in terms of its toxic effects. Some cleaning agents have masking agents to remove fragrance for chemically sensitive users or people wh o present with allergies. However, the molecule of fragrance still remains in the product.
Builders The term 'builders' is something used in discussing surfactants. In the case of cleaning agents, these builders are o ften present in detergents. Builders are substances that prevent other contaminants from reacting with the active ingredient in the detergent.
Masking agents A scent of a product is often underestimated in terms of its toxic effects. Some cleaning agents have masking agents to remove fragrance for chemically sensitive users or people who present with allergies. However, the molecule of fragrance still remains in the product.
Builders The term 'builders' is something used in discussing surfactants. In the case of cleaning agents, these builders are often present in detergents. Builders are substances that prevent other contaminants from reacting with the active ingredient in the detergent. Preservatives Cleaning agents that are stored for long term periods need some sort of preservative to keep the active ingredient functional. These may come in the form of salts, organic reagents, or buffers that maintain pH balance Antimicrobial reagents Microbes are often the cause of infection or cause some products to degrade. The purpose of a cleaning agent is to maintain the appearance or use of a certain material. Therefore it would make sense for an timicrobials to be present in cleaning agents. Bubble enhancers Adding bubble enhancers to allow detergents to do their job more effectively by enhancing the covered area of the surfactant. The formation of foam/bubbles facilitates the surfactant by aiding in the accumulation of unwanted particles. To summarize, the functions of additive ingredients are ( but not limited to the following): serve as disinfectant for hygienic purposes and to prolong the shelf life of the product enhance or mask a specific property; and protect the active ingredient from attacking other molecules
Examples Triclosan is an example of a n antimicrobial additive that reduces or prevents bacterial contamination. They are usually present in toothpastes and soaps.
Sodium tripolyphosphate is a common example of a builder found in detergents. It allows surfactants to work at their full potential. It also acts as a pH buffer and prevents deposition of soil.
Try it! Collect various samples of water (from the streams, seawater or tap water) and a control of distilled water. Add a drop of detergent in approximately the same amount of water. Shake well, and try to quantify the appearance of bubbles. What can you say about the bubbles? Key Points Additive ingredients are not innate, and they have a specific function in making the product what it is. There is a variety of additive ingredients with a variety of functions such as masking agents, enhancing agents, or preservatives. PERSONAL CARE PRODUCTS
At the end of the lesson, you should be able to give common examples of personal care products used to enhance the appearance of the human body. There are numerous personal care products you can find in grocery stores and shopping malls worldwide. What are these
personal care products? And why do people use them? Personal care products are consumer products used in personal hy giene and for beautification. These products have two classifications, personal hygienic items and cosmetics though there is only a small distinction between the two. Personal hygienic items are the products people use to keep themselves clean while cosmetics are often described as luxury products used for enhancement of physical beauty. Products for Personal Hygiene Shampoo and Conditioner Shampoo and conditioner are both haircare products. They are viscous liquids u sed to clean hair. They a re used by applying th em to wet hair, massaging them into the scalp, and rinsing them. Shampoos are particularly used to remove the unwanted buildup of dust and other particles on the hair without stripping out sebum. Sebum, a mixture of triglycerides, wax, and fatty acids, is secreted by the sebaceous glandin humans. The main function of sebum is to lubricate the hair and keep it manageable.
Hair conditioners are used to change the texture and appearance of hair. When shampoos strip out much sebum, hair conditioners provide the oils ( EFAs - essential fatty acids ) which function as natural sebum. These EFAs keep the hair softer and more pliable. Conditioners also often contain moisturizers, which hold moisture in the ha ir.
Soap Soap is a personal care product used for bathing and cleaning the skin. It can remove the oil and dirt particles adhered to the skin. These particles are often insoluble in water so they ca nnot be washed off by water alone. Soap breaks up these particles into smaller sizes and mixes them with water.
How does soap mix the insoluble particles with water? Soap is made up of fatty acids, which are molecules with two different ends – hydrophobic and hydrophilic ends. When mixed with water, the soap molecules form a micelle. The hydrophobic ends attach to the unwanted particle while the hy drophilic ends are attracted to water. So when water is used to rinse off the soap, dirt particles are washed away.
Facial Cleanser Have you ever wondered why there are marketed cleansers especially made for the face? Is there really a difference between the facial cleansers and body soaps? The skin on your face has more sebaceous glands than most parts of the body. Sebaceous glands produce sebum which lubricates the skin and protects it from bacteria. Sebum reaches the surface of the skin through the hair follicles. When sebaceous glands become overactive, too much sebum is produced. The sebum is combined with dead cells (keratin) which are naturally present in the skin, and their combination results in a plug. Because the follicle is plugged, the bacteria called Propionibacterium
acnes present in the skin proliferate. The bacterial growth causes acne, the painful inflammation and swelling of the facial skin. Acne and other facial skin diseases are often prevented using facial cleansers.
Facial cleansers remove makeup, dead skin cells, and dirt that can clog the pores. Best facial cleansers should have a pH near 4.7, the average pH of the skin’s surface. Bar soaps with high pH (9 to 10) can disrupt the pH balance of the skin and favor the
overgrowth of P. acnes. Also, the cleanser should not have thickeners which are present in bar soaps. These thickeners allow the soaps to form a rigid bar shape, but they can clog the pores resulting in acnes. Lastly, bar soaps may remove natural oils from the facial skin and cause sebaceous glands to overproduce sebum, which eventually lead to clogged pores.
Deodorant and Antiperspirant There are two types of sweat glands found in the skin, eccrine a nd apocrine glands. Eccrine glands can be found on almost all over the body, with the highest density in palms and soles. They produce sweat, an odorless substance comprised mostly of water and sodium chloride. They are active in thermoregulation because the evaporation of sweat has a cooling effect on the body. On th e other hand, apocrine glands are found only in certain a reas of the body, including armpits and some parts of external genitalia. These glands secrete an oily fluid which is odorless before microbial activity. The oily fluid is comprised of fats and proteins which are broken down by bacteria into certain acids with bad smell. The bad smell in the armpits is often masked using personal care products such as deodorant and antiperspiran
The terms deodorant and antiperspirant are often used interchangeably, but they a ctually differ. Antiperspirants control sweat and body odor by preventing sweat to reach the skin surface and by reducing the bacteria that cause body odor. Deodorants only contain antimicrobial agents to prevent body odor, but they do not control sweat. However, both of these products contain fragrances that mask the smell of body odor.
Toothpaste When you eat, some food stays on your teeth. This food can be broken down by mouth bacteria to form a sticky film called dental plaque . When plaque builds up and hardens, it forms tartar. Tartar is a crusty deposit that traps stains o n the teeth and causes discoloration. When tartar forms, bacteria will build up a nd damage the gums. Pockets between gums and teeth will f orm when the gums are infected with the bacteria. So to prevent the formation of plaque and occurrence of gum disease, teeth must be cleaned by brushing. Plaque begins forming 4 to 12 hours after brushing so it is important to brush teeth at least twice a day.
Toothpaste is a paste or gel used with a toothbrush to remove food from the teeth and kill the bacteria which cause bad breath. It contains abrasives which scrub away stains and plaque on your teeth. Abrasives also polish the teeth so they look fresh and clean after brushing. Cosmetics Cosmetics are substances or products used to enhance the appearance or scent of the body without affecting the body’ s structure and functions. Common cosmetics include facial makeup and fragrances. Facial Makeup Generally, women use more cosmetics than men. Many women apply facial makeup to enhance their facial features or cover imperfections of the skin. They use products such as foundation, concealer, lipstick, lip gloss, lip balm, blush, eyeshadow pencil, mascara, and eyeliner. Foundation is used to cover blemishes and even out skin color. When extra coverage is needed to conceal acne and undereye circles, a concealer is used. A concealer is often thicker and more solid than foundation so it can provide longer lasting cov erage of skin imperfections. Lipstick is intended to add color and texture to the lips. It is different from a lip gloss which is intended to a dd shine to the lips. Lip balm is also used to add color, but its main purpose is to moisturize and protect the lips from chapping. Blush or rouge is used to add color to the cheeks to make them look more defined. Different colors of blush compliment different skin tones. Eyeshadow, eyebrow pencil, and mascara are all used to accentuate the eyes. The eyeshadow is used to add color on the eyelids and under the eyebrows to make the eyes more attractive while eyebrow pencil is used to darken the eyebrows to make them more defined. Mascara is applied to darken the eyelashes and make them appear longer and thicker. Cosmetics Cosmetics are s ubstances or products used to enhance the appearance or scent of the body without affecting the body ’s structure and functions. Common cosmetics include facial makeup and fragrances. Facial Makeup Generally, women use more cosmetics than men. Many women apply facial makeup to enhance their facial features or cover imperfections of the skin. They use products such as foundation, concealer, lipstick, lip gloss, lip balm, blush, eyeshadow pencil, mascara, and eyeliner. Foundation is used to cover blemishes and even out skin color. When extra coverage i s needed to conceal acne and undereye circles, a concealer is used. A concealer is often thicker and more solid than foundation so it can provide longer lasting cov erage of skin imperfections. Lipstick is intended to add color and texture to the lips. It is different from a lip gloss which is intended to a dd shine to the lips. Lip balm is also used to add color, but its main purpose is to moisturize and protect the lips from chapping. Blush or rouge is used to add color to the cheeks to mak e them look more defined. Different colors of blush compliment different skin tones. Eyeshadow, eyebrow pencil, and mascara are all used to accentuate the eyes. The eyeshadow is used to add color on the eyelids and under the eyebrows to make the eyes more attractive while eyebrow pencil is used to darken the eyebrows to make th em more defined. Mascara is applied to darken the eyelashes and make them appear longer and thicker.
Fragrances Have you ever flipped through a catalogue of beauty products and found different names for fragrances? Cologne, eau de toilette, and perfume are the common names of fragrances. They all contain essential oils, such as vanilla, rosehip, and peppermint oils, that are diluted with a solvent such as ethanol, propylene glycol, and water. The difference among these fragrances is the concentration of the essential oil.
Cologne is a shortened version of “eau de Cologne.” Eau is the French word for water while Cologne came from the French city “Koln” where a particular scent was first made. Cologne is the most diluted fragrance, with about 2 to 5% essential oils. It often smells sweet and fruity. Because it has less essential oils and higher percent alcohol, its smell do not last very long compared to other fragrances. It is not viscous so it is often applied by “splashing” it in the body.
Eau de toilette or toilet water has more concentration of essential oil compared to cologne. It has about 5 to 15% oil. Because it has more oil compared to alcohol, it is more viscous and is often sold in spray bottles.
Perfume is the most concentrated of all the fragrance options so it is also the most expensive. It has about 15 to 40% essential oils. It has thicker and oilier consistency so it is often in stopper bottles.
Why is it important for you to understand the chemistry of personal care products?
Key Points Personal care products are consumer products used in personal hy giene and for beautification. Personal care products include shampoo, hair conditioner, soap, facial cleanser, deodorant, antiperspirant, toothpaste, facial makeup, and fragrances. THE MAJOR INGREDIENTS OF PERSONAL CARE PRODUCTS
At the end of the lesson, you should be able to identify the major ingredients of personal care products. In the previous lesson, you have l earned about personal care products and the reasons why p eople use them. Some of their ingredients may differ from how cleaning agents work but one thing is certain –the active ingredients for cosmetic products need to have a non-toxic concentration on humans.
Personal care products are products that people use for personal hygiene and beautification. Different personal care products that we usually use a re listed below as well as their acti ve ingredients.
Deodorants The major ingredients of deodorant include aluminum-based compounds such as aluminum chloride, aluminum chlorohydrate, and aluminum zincronium. A complex coordination compound involves a central atom (usually a metal ion) and ligands that share its electrons with the electropositive central atom.
In deodorants, the aluminum compound usually forms a complex coordination compound. Aluminum chlorohydrates is a general group of compounds that have coordinate covalent bonds. These compou nds block pores and the sweat glands in the armpit.
Body Lotions Body lotions can be classified as emulsions. Emulsions are dispersions of fine particles that do not dissolve in a medium. An emulsifier is a class of surfactant that is usually added to make two immiscible substances miscible. Cetearyl alcohol is an example of an emulsifier.
Note the evident formation of micelles by the emulsifier molecule, allowing two immiscible phases to dissolve.
The ability of a certain molecule to attract atmospheric moisture or moisture, in general, is called hygroscopicity. Compounds such as glycerol are added to products that are meant to be retained on the skin. The structure of glycerol makes it a very viscous substance due to very strong intermolecular forces. Furthermore, it is also a polar molecule which allows it attract water molecules. The glycerol molecule is also the backbone of a triglyceride molecule. A triglyceride molecule, upon hydrolysis, will release one molecule of g lycerol and three molecules of fatty acids.
Perfume A perfume will contain essential oils and glyc erol as its major components. Essential oils are naturally extracted oils from plant or animal sources that have a strong fragrance. You will notice that most of these compounds are organic by nature, a nd will require an organic solvent. Essential oils are a group of volatile organic compounds. In contrast to glycerol, they have relatively weak intermolecular forces, allowing their scent to be easily dispersed. As with most organic compounds, essential oils can be classified a s alcohols, aldehydes, esters, and others. Unsaturated molecules generally have weaker intermolecular forces compared to their saturated c ounterparts.
Shampoo/Conditioner Major ingredients of shampoos include surfactants that form micelles. These shampoos usually use ammonium compounds due to their high versatility to function as a surfactant and thickening agents. Ligands such as EDTA (Ethylene Diamine Tetraacetic Acid) i s added to help preserve the shampoo from reacting with metals which can ruin the quality of the product. EDTA is a commonly used chelating agent with a high affinity towards most metals
Soaps Specialized soaps for skin are still made of surfactants that act the same way as detergents. The application of surfactants can also be found in hand lotions, shampoos, and conditioners.
Make-ups Make-ups are usually made up of colored pigments and/or metal oxides. Pigments and metal oxides give color due absorption of visible light at a certain wavelength. This absorption is possible due to certain structural configuration or electronic transitions.
Electronic transitions are made possible by movement of electrons to empty orbitals as with the case of adjacent double bonds (conjugation) or transition metals.
Such is the case with carminic acid which gives the color red, due to the presence of multiple conjugated sites.
Explore! The realm of cosmetics is not an invention of the 20th century due to fashion and a high standard of living. Cosmetics has been in practice as early as the time of the Greeks, all the way to modern civilization. Furthermore, not all cosmetic practices today have been modernized, more than beautification, cosmetics have a cultural impact. What are some examples of ancient cosmetic products that have their closest modern day contemporaries? How do we make sure that our personal care products remain safe? What hazards are present in handling these products? Key Points Personal care products are products that people use for personal hygiene and beautification. Cosmetic products can have more than one major ingredient that works hand in hand to make a certain product functional. Active ingredients have multiple mechanisms such as surfactants, coordination complexes, moisturizers, emulsions and special receptor interactions. Others work due to their natural properties such as scent and color.
THE PRECAUTIONARY MEASURES INDICATED IN VARIOUS CLEANING PRODUCTS AND COSMETICS
At the end of this lesson, you should be able to explain the precautionary measures indicated in various cleaning and persona l care products.
How do you choose a cleaning or personal care product? How do you read their labels? You often choose a cleaning or personal care product based on its effectiveness, popularity, and price. Have you also considered its effect on your health and on the environment? Effects on Human Health Personal care products are applied on the body, so there is a possibility that their ingredients enter the body through skin absorption or by ingestion. Therefore, it is important that these products are healthy and nontoxic. When choosing a personal care product, learn to read the labels. Be aware of toxic substances that may be found in the product you want to buy. Below are some of the substances you have to avoid. Poisonous heavy metals such as lead, arsenic, and mercury can be found in a wide range of personal care products. When these heavy metals enter the body, they can accumulate and replace the metals that are normally present for specific functions in the body. They can often be found in products such as whitening toothpaste, lipstick, sunscreen, and c oncealers. Hydroquinone is often found in skin lighteners and facial cleansers. This substance has been reported as a cancer-causing agent an d respiratory tract irritant. It has been banned in E urope and restricted in Canada. However, many p roducts sold in Asia still contain hydroquinone. Phthalates are substances often found in color cosmetics, fragrance lotions, and hair care products. They a re linked to endocrine disruption and reproductive toxicity. They are often written in labels as phthalate, DEP, DEHP, or DBP. Choose products labelled "phthalate-free," but consider their other ingredients. Nitrosamines are substances produced by diethanolamine (DEA) and truethanolamine (TEA) which are both found in nearly every kind of personal care product. They cause organ system toxicity and endocrine system disruption. It is safe to avoid products containing DEA and TEA. Effects on the Environment Cleaning products are often disposed in the environment. For instance, detergents are mixed with water that goes down the dra in. Hence, the detergent may find its way into the ground and into bodies of water. It is important that these products are safe for the environment. Below are some properties you need to consider in buying products. Corrosive These corrosive products are often presented in dilute amounts, some, may not be even harmful upon acute exposure. However, prolonged exposure (if not immediately washed and rinsed with water) can lead to corrosive burns.
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