CHEMISTRY 3A General Information and Experiments
CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFO RNI A
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Chemistry 3A Experiments Experiment
Project Pyro
Time
Points
3 hrs
100
6 hrs
200
6 hrs
300
9 hrs
400
Construction of a Roman Candle Project Glow
Kinetics and Mechanism of Ru(bpy) 32+ Project Ester
Synthesis of Aspirin Project Werner
Synthesis of Cobaltammine Characterization of Cobaltammine
Website This lab manual, lecture notes, and TA contact information can be found on the Chem 3A website: http://chemlabs.caltech.edu/wiki/ch3a:home
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EXPERIMENT 1 A Simple Demonstration of Pyrotechnics Historical Background Chemical knowledge has been used throughout history in the extraction of crucial elements from ores, the synthesis of medicine, the molding of plastics into a variety of lightweight materials, and many other amazing processes.
These
processes are all very useful, and without them our lives would be dramatically different, but often they are not dramatic themselves. One of the most ancient and dramatic uses of chemistry is the manipulation of fire in its many forms. Fireworks were believed to be first used in China in the 7 th century, where they were used in a variety of cultural celebrations. Early use was primarily limited to noise markers with light as a byproduct. By the ninth century fireworks were so commonplace in China that they were sold by street venders for individual purchase and used in both family celebrations and dramatic imperial productions. We most often see a fireworks display on the 4 th of July or following a professional sports event; an explosion of red, yellow, and blue showering down from the skies accompanying a patriotic soundtrack is commonplace.
The
elaborate displays compete with one another to be the highest, largest, and most original. It is now common to see a single firework explode in a burst of green, followed by red sparks, or any other color and effect combination. In recent years fireworks manufacturers have manipulated the packing structure of fireworks to have individual devices explode into simple shapes like stars and hearts. Many of us can still remember a time when our parents were permitted to purchase fireworks and set them alight in front of our homes on the 4 th of July. In order to reproduce that thrill, and to teach you a couple of the most basic chemical reactions, we will construct our own firework.
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Chemical Background You will design and build your own Roman Candle using some very simple chemical knowledge, common lab materials, and a few salts & elements found in the chemistry storeroom.
In doing so, you will learn about three of the most
common chemical reactions: oxidative combustion, decomposition reactions, and double replacement reactions. The basic chemistry behind all fireworks is combustion (burning).
Burn the
right chemicals at the right time and you will get a beautiful display. But just how do you control that burn? Combustion requires three things: fuel, oxygen, and an ignition source. In order to control combustion, we must control the input of at least one of these “ingredients” to the reaction. Doing so will give us some control of the reaction. Spark
CH 2O( s ) + O2( g ) ⎯ ⎯⎯ → CO2( g ) + H 2O( g ) Equation 1. Basic combustion equation of generic organic mater. Fuel and oxygen combust to give carbon dioxide (the oxidized product) and water (the reduced product). Combustion of metals is also possible (as we will see), where the elemental metal is oxidized and combines with oxygen.
In the above reaction, control of either oxygen or the spark will control the reaction. This can be seen in the simple action of lighting a match. At any given moment a match stick (fuel) is exposed to the air (oxygen); it is only after a person strikes the match against the box producing a spark does the reaction have all three components to proceed and combustion begins.
We will preform a more
sophisticated version of this combustion reaction for our Roman Candle. A Roman Candle is a device which burns an intensely hot and bright flame of different colors in a sequence. In order to achieve the intense hot flame we need to not only use a good fuel, but we must augment the reaction with extra oxygen. We will supply this oxygen with a decomposition reaction.
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3 O → KCl( s ) + KClO3( s ) ⎯ ⎯⎯ 2 2( g ) Heat
Equation 2.
The decomposition of potassium chlorate to produce potassium chloride and
molecular oxygen. We will use this oxygen to fuel our Roman Candle. This reaction has a large activation energy which we must supply.
When potassium chlorate is heated the chlorate decomposes into chloride and oxygen gas.
By taking advantage of the extra oxygen supplied by the
decomposition of potassium chlorate, our combustion will be intense enough to burn any metal or salt added to the Roman Candle.
But how will we safely
(remotely) overcome the activation energy? We will use another important chemical reaction to get the spark, the double replacement (displacement) reaction. In a double replacement reaction, the ions of two ionic compounds exchange with each other to form two new compounds. There are many examples of these throughout chemistry, an acid-base reaction is a specific type of double replacement reaction, where an acid and base react to form water and a salt. We will use a double replacement reaction involving potassium chlorate (again) with sulfuric acid.
KClO3( s ) + H 2 SO4 ( l ) HClO3( aq ) + K 2 SO4( aq ) Equation 3. The double replacement reaction between sulfuric acid and potassium chlorate to produce chloric acid and potassium sulfate (unbalanced). This reaction is driven to completion due to chloric acid’s explosive nature in the presence of organic matter.
In this reaction the liquid sulfuric acid dissolves the potassium chlorate, then the potassium and hydrogen cations exchange to form a new acid (chloric acid) and a salt, potassium sulfate. The production of chloric acid is the key result. Chloric acid is explosive when it comes in contact with organic matter (careful!) Therefore, if we have a mixture of potassium chlorate and an organic material (sugar) and add a small amount of sulfuric acid, we will get a spark, Eq. 3. That spark will decompose the remaining potassium chlorate producing ample oxygen, Eq. 2, which can combust the remaining sugar, Eq. 1, resulting in the intense flame we desire.
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In order to achieve colorful flames, we add a variety of salts and elements which combust giving off different colors. Just as hydrogen gives off a specific set (spectrum) of colors when its electrons relax from their excited to ground state (Oxtoby, Gillis, and Campion, page 151), different metals each have a unique spectrum. This spectrum of colors is mostly seen as a single color, for instance the combustion of elemental iron to an iron oxide gives a yellow color, even though the spectrum has multiple color bands. An image of the iron emission spectrum can be found on the Chem 3A website. The excitation of electrons results from the combustion of metals to their oxides, or the decomposition of salts to simpler products.
The combustion of
elemental metal results in a metal oxide, (the oxidation state of the metal can vary but generally takes the most stable form, Eq. 4).
4 Al( s ) + 3O2( g ) → 2 Al2O3( s ) 2Cu( s ) + O2( g ) → 2CuO( s ) Figure 4. Combustion of metals results in a metal oxide, with a metal oxidation state which is most stable. For aluminum, the ionic oxidation state is always +3, for copper the most stable oxidation state for the ion is +2.
Salts do not combust, rather, they decompose in a predictable way. In general, metal salts decompose into either a metal, metal oxide, or a simpler salt. Metal chlorides decompose into the elemental metal and molecular chlorine gas. Metal carbonates decompose to their metal oxide and carbon dioxide (Eq. 5).
MCO3( s ) → MO( s ) + CO2( g ) Equation 5. The decomposition of a generic metal oxide. The CO32- ion decomposes into ionic oxygen and molecular carbon dioxide. The oxygen remains with the metal forming a metal oxide. The metal does not change oxidation states.
We can explain this phenomenon by looking at the electronic structure of the carbonate ion (Fig 1). The lone ion evenly distributes electron density between the three oxygen atoms, and away from the central carbon, figure 1a. When a positive
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ion, such as the metal comes in contact with the carbonate, the electronic distribution favors the oxygen nearest the metal, figure 1b. This weakens the C-O bond between the oxygen nearest the metal and strengthens the ionic bond between the metal and oxygen.
When heated, the
ion can split at this C-O bond forming a carbon dioxide molecule and a thermally stable metal oxide. Metal nitrates behave in a similar manner.
Group 2 nitrates and LiNO 3
decompose to a metal oxide with nitrogen dioxide and molecule oxygen (Eq. 6a).
The remaining group 1
nitrates decompose into a metal nitrite and molecular oxygen (Eq. 6b).
Figure 1. The electronic structure of the
carbonate ion.
(a) A majority of the electron
density is evenly distributed around the outside oxygen atoms. (b) When a metal ion nears, the electron density shifts towards the cation.
Heat
2 M ( NO3 )2( s ) ⎯ ⎯⎯ → 2 MO( s ) + 4 NO2( g ) + O2( g ) Heat
2 MNO3( s ) ⎯ ⎯⎯ → 2 MNO2( g ) + O2( g ) Equation 6. Group 2 nitrate decompose into the thermally stable metal oxide, resulting in the evolution of nitrogen dioxide and molecular oxygen. Lithium nitrate behaves in this manner; however, the other group 1 nitrates decompose into metal nitrite and molecular oxygen.
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We will use the combustion of metals in their elemental or salt forms to design unique flames for the Roman Candle. Table 1 has a list of metals which you may wish to use in your Roman Candle as well as the colors associated with them. Metal
Color
Useful Form
Antimony
Glitter
Sb2O3
Barium
Green
BaCl2
Calcium
Orange
CaCl2
Copper
Blue-Green
CuCl2
Iron
Yellow
Fe
Lithium
Red
Li2CO3
Magnesium
White
Mg
Potassium
Purple
KNO3
Sodium
Yellow-Orange
NaNO3
Strontium
Red
Sr(NO3)2
Table 1. The metals in the above table will give off a variety of colors, you can use any three of these in your Roman Candle. The final column is used to determine how much colorant is needed in the potassium chlorate-sugar mixture.
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Prelab Read page iv of this manual’s introduction and complete the prelab. 1. Construct a table within your lab notebook, with rows (or columns) representing each chemical used and columns (or rows) for: molecular mass, density, melting point, and boiling point. Fill out the needed information for each chemical. 2. Read the procedure below, add a column (or row) for moles used, and then calculate the masses (or volumes) needed for each chemical to be used. 3. Add one additional column (or row) for any material safety data sheet (MSDS) cautionary handling notes. 4. Outline the procedure in your notebook such that you will not have to refer to this manual while you are in the lab. Questions 5. Write a balanced chemical reaction for the combustion or decomposition of a. Ethanol
d. Iron (III) Chloride
b. Octane
e. Iron (II) Carbonate
c. Iron f. Iron (II) Oxide 6. Write a balanced chemical reaction for the reaction of: a. Sodium hydroxide with hydrochloric acid b. Sodium nitrate and potassium chloride c. Silver nitrate and iron (II) chloride 7. Write a balanced chemical reaction a. Iron with aqueous copper (I) nitrate b. Magnesium with aqueous nitric acid c. Copper with aqueous hydrochloric acid 8. Calculate the volume of hydrogen gas produced when 2 g of Zn is added to 5 mL of concentrated HCl. State all assumptions.
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Procedure Collect two test tubes. Pour 3-4 mL of concentrated hydrochloric acid (HCl) in one test tube.
Invert a second test tube over the first, leaving a small space
between the two tubes. Mass out and then carefully drop about 1g of zinc into the HCl, closing the space between the test tubes to collect the gas. After collecting gas for about a minute (keeping the top tube inverted as to not let the gas escape), you may ignite the gas with an open flame. Collect the watch glasses and a test tube from your drawer.
Lay the watch
glasses out inside your hood, and clamp the test tube to one of the vertical bars at the rear of the hood. Mass out 0.5 g each of potassium chlorate (KClO 3) and sugar. Grind these two chemicals separately and place the powders in separate watch glasses.
Add about 2 mL of H 2SO4 to the test tube.
It is important to label
chemicals. Use your pen and lab tape to mark either the containers or counter top where they lie. You may also place a white napkin under the watch glasses to make the resulting colors stand out better.
① Use your spatula to place a small
scoop of KClO 3 into an empty watch glass. Use your small (2 mL) pipette bulb and one of the disposable pipettes on your station’s shelf to add a small amount of sulfuric acid (H2SO4) to the top of this small amount of KClO 3. You may add more H2SO4 if you need. Record your procedure and observations in your notebook.
②
Place a small amount of sugar into an empty watch glass. Add a small amount of H2SO4 to the top of the powder, record the procedure and results.
③ Place small
equal parts KClO 3 and sugar into an empty watch glass. Mix the powders gently with the end of your spatula. Add one drop of H 2SO4 to the top of the mixed powders.
④ You may repeat this experiment if you wish, adding an equal amount
of a colorant to the mixture.
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Roman Candle Begin your Roman Candle by assembling the hardware structure. Fill a 400 mL beaker with sand and insert a test tube into the center of the sand-filled beaker. In a mortar and pestle grind 0.1 mol of potassium chlorate (KClO 3), followed separately by 1.5 x 10 -2 mol of sugar. Mix these two chemicals in a new beaker and set them aside for later use. Do not grind theses chemicals together due to the risk of fire! Choose three colors (chemicals) to include in your Roman Candle and the order in which you would like them to burn. The possible colors and the chemicals needed can be found in Table 1. As an example, I will describe the procedure used for a Roman Candle first burning yellow (iron), followed by blue (copper (II) chloride), and finally red (strontium nitrate). Starting with the last chemical to burn, mix 5 x 10-3 mol strontium nitrate and
¼
of the potassium chlorate-sugar mixture in a small
beaker. Using a piece of weighing paper or powder funnel pour this mixture into the test tube embedded in the sand. In the same manner, mix 5 x 10 -3 mol of copper (II) chloride with
¼
of the potassium chlorate-sugar mixture and pour it into the test tube,
on top of the strontium mixture. Next, mix 5 x 10 -3 mol of iron powder with
¼
of the
potassium chlorate-sugar mixture and add it to the top of the test tube. Lastly, add the remaining potassium chlorate-sugar mix to the test tube. Tell your teaching assistant or instructor when your Roman Candle is completed. The majority of the Roman Candles will be set off at 10:30PM during the Wednesday night section on the Beckman Institute Lawn. The T.A.’s will direct you to the place and time if there are changes.
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1st Weekly Assignment
(10 points)
Throughout Chem 3A, at the conclusion of each week, you are required to submit figures which represent the work accomplished during that week (Due the Friday following the experiment at 4 PM).
This week’s assignment will be an
introduction to this activity. Due Friday Oct. 12 at 4 PM 1. Write a balanced reaction for the production of chloric acid within the Roman Candle. 2. Write a balanced reaction for the production of oxygen within the Roman Candle. 3. Write a balanced reaction for the combustion or decomposition of the metals and salts you used as colorants within the Roman Candle. 4. Illustrate a figure showing the construction of your Roman Candle.
Each figure, equation, table, or plot turned in must be computer generated and include a detailed figure caption. A proper caption will contain three elements: 1. A title. This will look like: “Figure 1. Balance equation for the reaction between hydrochloric acid and sodium hydroxide.” 2. An explanation. Explain to the reader why the plot is important. This should be one sentence. If you are not sure what to write, perhaps the figure isn’t important enough to include. 3. Key point. Explain to the reader what should be taken from the material presented. This is a second or third sentence describing the important or curious points of the figure.
Be concise and direct with these points.
discussed in the body of your report.
Any further explanation can be
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Final Report Grading Scheme
(50 Points Possible)
Scientific reports contain 5 parts: abstract, introduction, results, discussion, and conclusion. Throughout the term you will write experimental reports following this format.
It is hoped that repeating this task will lead to exceptional report
writing. The pages that follow are designed to guide you throughout the report writing format. Please refer to them throughout the term if you have questions. Reports should be structured in the order listed below; however, you should not write it in this order. The most important sections are the Experimental/Data and Discussion sections, begin your report on the Experimental/Data section in order to fully understand the data you have, then move onto the Discussion section. Spend the vast majority of your time on these two sections. Next work on the Conclusion and Abstract sections, which are very similar in structure.
Finally, write the
introduction. 1. Abstract - 1 paragraph A brief conclusion of the experiment so the reader knows what to expect from the report. Generally, it is structured in 3-5 sentences and uses very specific results and conclusions. Avoid general statements like the results were “good”, “positive”, or “large”, actually state the numerical result. Finally state the actual result or conclusion, the reader will want to know if your paper is worth reading. 2. Introduction - 1 page The most difficult section to write. (Work on this last.) A proper introduction relates the past advances in the field to the reader complete with citations (style of citation is unimportant in our case). It should outline the major work done and the gaps in knowledge or technology. The introduction should also introduce key facts that the reader must know to understand the paper. Items such as, electron structure, general reaction scheme, important chemical or physical properties, and why these are important to know. Lastly, it should tell the reader what your experiment does to address the questions in the field.
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3. Experimental / Data (Results) - Length will vary, needs to be complete The Data section need not have much written language, but it needs to describe the experiment and present all your data in a clear effective manner. This is where all your raw data goes, use lots of tables and figures. Brief statements of the data may or may not be required. Many people are uncomfortable with a section with few words and many tables etc, so they combine it with the Discussion section. I feel this is a mistake. 4. Discussion - Length will vary, needs to be complete The discussion section is the most important section in a science paper. This is the section where you explain all your data. You should have processed data within this section. For example, if you have a series of standard and sample data plotted in the data section, the discussion section will have the analysis of those samples and comparison to the standards. You will state why you did any calculations (not how) and what the result means. Please do not do a sample calculation, do state the equation you used to calculate the result, (we will assume your algebra is correct). Results should be recorded in a table. Draw conclusions and state the results in positive specific terms, as in the abstract, avoid relative language- it is vague. 5. Conclusion - 1 - 2 paragraph(s) The conclusion needs to summarize the data and discussion without restating them. State the major points of the processed data and end results of any calculations you made. State specific results and why they are important. Make sure you have a final positive statement summarizing and concluding your paper and the experiment you conducted.
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The first task you must complete before you write a report is to understand your data thoroughly. The best way to do this is to plot your data in a meaningful way. You have already done this by constructing figures after last week’s experiments. The second step is to outline your thoughts in order to convey your story. Although sometimes tedious, outlines can greatly help the flow and efficiency of your message. The last step is to fill in the outline with your story’s details. For this first report, I will provide the outline, you will use it to write only the results and discussion sections. (Due on Friday Oct. 19 at 4 PM). Follow the outline below (and on the next page): I.
Results A. Experimental Procedures 1. Write a brief description of each experiment a. Zn + HCl b. KClO3 +H2SO4 c. Sugar +H2SO4 d. KClO3 +Sugar + H2SO4 e. Roman Candle 2. Include a diagram of experimental set-up, if you believe it would help. B. Observational Results 1. Write your observations from each experiment. 2. Add photos, if you took them. The experimental observations may be written directly following each experimental description. II. Discussion A. Zn +HCl 1. Write the complete and balanced reaction involved 2. Discussion the reaction. a. Address driving force behind the reaction. b. Calculate the theoretical volume of gaseous product. c. Address the reaction for the combustion of the product. i. Write the complete and balanced reaction. B. Roman Candle Chemistry 1. KClO3 + H2SO4 a. Write the complete and balanced reaction involved b. What kind of reaction is this? c. What are the products, why are they important? 2. Sugar + H2SO4 a. Generally, what happens to the sugar? 3. Watch glass - KClO3 + Sugar + H2SO4 & Roman Candle
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a. b. c.
4.
Write the complete and balanced reactions involved Why is this equilibrium reaction driven to completion? In your own words describe the sequence of reactions which ignited your Roman Candle, starting with the drops of acid and ending with the final layer of material. Colorants a. What three colorants did you use? b. Write the complete and balanced reaction for combustion of each metal or decomposition of each salt in your Roman Candle. c. For each metal, find the emission spectrum d. What color did you observe? e. Discuss the difference between the color observed and emission spectrum.
