Handy Chemistry Summary notes •
Chemistry 5073 / 6092 Summary notes * denotes important concepts or definitions that you have to know.
Topic
Concepts / Explanations / Definition Definitionss
Unit 1 : Experimental Chemistry Experimental Experimental Design Design Introduction
Measureme nts
Chemistry is an experimental science. Chemistry is the study of the properties of matter, including transformations that matter m atter undergoes, also known as chemical reactions. Properties of matter such as volume, temperature, mass, etc. are measured quantities. The volume of a liquid can be measured using:
Beaker
Measuring Cylinder Less accurate
Methods of gas collection
Pipette
Burette
More accurate
The volume of a gas can be measured using a syringe: Depends on the density and solubility in water. Air consists of mainly nitrogen and oxygen oxygen gases. If soluble, Denser than air (than N2, O2) – downward – downward delivery e.g. CO2 cannot collect Less dense than air (than N2, O2) – upward – upward delivery e.g. H e.g. H2 over water All gases which are insoluble in water can be collected over water. water.
Topic Purity of a substance
Concepts / Explanations / Definition Definitionss A pure substance is a single single substance not mixed mixed with anything else. It will melt/boil at a constant and fixed temperature. fixed temperature. An impure solid will melt over a range of temperatures, which temperatures, which is lower lower than than that of the pure solid. e.g. e.g. Naphthalene, the substance used for moth balls, has a sharp m.p. of 79oC (means as the solid is melting, the temperature is unchanged). Impure naphthalene will start to melt at 75oC and continue melting until 78.5oC when all is completely melted. An impure liquid will boil over boil over a range of temperatures, temperatures , which is higher than than that of the pure liquid at a given pressure (1 atmosphere or 101.325 kPa). e.g. e.g. Pure water: b.p.- 100 0C , sea water – water – 103 103oC at normal pressure. Refer to the graphs in your textbook. An impure sample of a substance is really really a mixture of two or more substances that can be separated by different physical methods.
Methods of purification
Solution: Solution: Contains a solvent (usually solvent (usually water, sometimes it is an organic solvent such as chloroform or alcohol) and a solute (NaCl, sugar etc). If water is the solvent, the solution is called an aqueous solution. aqueous solution. Saturated solution is solution is a solution which contains the maximum mass of mass of dissolved solute in a given volume of solvent (usually water) at a given temperature. The higher the temperature, the more solute can generally be dissolved. dissolved. Different solutes have different solubilities in water at a given temperature. Evaporation Evaporation and Crystallisatio n : Evaporate to obtain a hot and saturated solution. Cool and crystallize to obtain the crystals of sol ute. Cannot ute. Cannot evaporate to dryness.
Topic
Concepts / Explanations / Definition Definitionss
Filtration : To separate a solid from a mixture of insoluble insoluble solid from a liquid, Example: Sand and seawater: filter to obtain the sand as residue (insoluble part) and seawater as the filtrate (soluble filtrate (soluble part).
Distillation: To separate a solvent from a solution by boiling. Example: distill seawater to obtain pure water (distillate). Salt from the seawater is left behind.
Fractional distillation : To separate a mixture of miscible liquids with liquids with different boiling points. First fraction is the one with the lowest boiling point. Example: water (b.p. 100oC) and ethanol (b.p. 78oC). Ethanol is the first fraction.
Topic
Concepts / Explanations / Definition Definitionss
(Paper ) Chromatography: Chromatography : Only a very small sample is sample is required. Different Different components in the mixture are soluble in t he same solvent to different extent. The more soluble component will move up the paper faster. Use of locating agent agent (such as ninhydrin to detect amino acids used for forensic tests) for colourless compounds. Determine Rf value =
distance moved by spot distance movedby solvent
Sublimation : Direct transformation from solid to gas. Only for mixtures containing I2(s), NH4Cl crystals, solid carbon dioxide and naphthalene. Solid carbon dioxide also sublimes at a low temperature.
Separating Separating f unnel: Only for immiscible liquids, liquids , e.g. chloroform and water, oil and water.
Topic Identificatio n of ions and gases
Concepts / Explanations / Definition Definitionss An inorganic compound compound contains a cation (positively charged ion) ion ) and an anion (negatively charged ion) ion ) To identify a compound, you will have to t o describe the tests carried tests carried out and the expected observations for both cation both cation and anion. anion .
Tests for cations
Add aqueous NaOH until NaOH until a change is seen and then excess. Add aqueous NH3 until a change is seen and then excess. Catio n NaOH(aq) NaOH(aq) NH3(aq) NH4+ On warming, NH3 gas the only produced, turned moist red litmus non-metal blue. cation *Recall: Alkalis + ammonium salt salt + ammonia + water Ca2+ White ppt, White ppt, insolu ble in excess excess No ppt 2+ Cu Blue ppt , ppt , soluble in soluble in excess Blue ppt, insoluble to form dark blue solution
Fe2+ Fe3+ Zn 2+
Tests for anions
Alternative test for iodide ions
The same as with NaOH White ppt, soluble in soluble in excess White ppt, White ppt, soluble in soluble in excess to to form a colourless colourless solutio 2+ form a colourless solution Pb White ppt, insoluble in White ppt, excess Al 3+ Different reagents are used to test for different anions. The reagent given will tell you what anion to look for. Anio An io n Test Obs ervati erv ati on Reaso n Cl Add AgNO3 followed White ppt insoluble in the White ppt of AgCl by dilute HNO3 acid is insoluble in water. I Add Pb(NO3)2 Bright yellow ppt Bright yellow ppt of PbI2 is insoluble in water. I Add AgNO3 Yellow ppt Yellow ppt of AgI is formed. SO42-
NO3-
Dirty green ppt, insoluble Reddish-brown ppt, insoluble
Add Ba(NO3)2 followed by dilute HNO3 Add aqueous NaOH and Al foil/powder and warm
White ppt insoluble in the acid Effervescence seen. NH3 gas produced turned moist red litmus blue
White ppt of BaSO4 is insoluble in water. Reduction of nitrate to form ammonia gas.
Topic
Tests for gases R.A. reducing agent O.A. – O.A. – oxidizing agent
Concepts / Explanations / Definition Definitionss CO32- Add dilute HNO3 On warming, Acid reacts with effervescence seen. CO2 carbonate to gas produced forms white produce carbon ppt with limewater OR dioxide gas. Gas turns limewater milky. Gas Gas Source Test Test and observatio n H2 Mg + 2HCl → MgCl2 + H2 Gas extinguishes a lighted splint 2Na +2H2O → 2NaOH + H2 with a ‘pop’ sound (R.A.) Metal + acid or alkali metal + water O2 Catalytic decomposition of hydrogen (O.A.) peroxide (O.A. stands for oxidising agent) NH3 NaOH + NH4Cl→ NaCl + H2O + NH3 Base + ammonium salt CO2
CaCO3 + 2HCl →CaCl2 + H2O+ CO2
Cl 2 Action of MnO2 (O.A.) on conc. HCl (O.A.) SO2 Action of acids on sulfites (R.A.) Na2SO3 +2HCl →2NaCl + H2O +SO2 Sulphite ion (SO32-) is usually not tested in the new syllabus.
Gas relights a glowing splint
Gas turned moist red litmus blue
Gas formed white ppt when passed through limewater Gas turned damp blue litmus red then bleached Gas turned filter paper strip dipped in acidified potassium manganate, KMnO4, from purple to colourless
