Ch3a Manual
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Transcript of Ch3a Manual
C A L I F O R N I A I N S T I T U T E O F T E C H N O L O G Y
PASADENA, CALIFORNIA
CHEMISTRY 3AGeneral Information and Experiments
Chemistry 3A Experiments
Experiment Time Points
Project Pyro 3 hrs 100
Construction of a Roman Candle
Project Glow 6 hrs 200
Kinetics and Mechanism of Ru(bpy)32+
Project Ester 6 hrs 300
Synthesis of Aspirin
Project Werner 9 hrs 400
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 1A Simple Demonstration of Pyrotechnics
Historical BackgroundChemical 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 7th 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 4th 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 4th 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.
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.
CH2O(s ) +O2(g)Spark⎯ →⎯⎯ CO2(g) + H2O(g)
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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.
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.
KClO3(s )Heat⎯ →⎯⎯ KCl(s ) + 32O2(g)
KClO3(s ) + H2SO4(l ) HClO3(aq) + K2SO4(aq)
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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).
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).
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
4Al(s ) + 3O2(g) → 2Al2O3(s )
2Cu(s ) +O2(g) → 2CuO(s )
MCO3(s ) → MO(s ) +CO2(g)
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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 LiNO3
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.
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.
2M (NO3)2(s )Heat⎯ →⎯⎯ 2MO(s ) + 4NO2(g) +O2(g)
2MNO3(s )Heat⎯ →⎯⎯ 2MNO2(g) +O2(g)
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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 FormAntimony Glitter Sb2O3
Barium Green BaCl2
Calcium Orange CaCl2
Copper Blue-Green CuCl2
Iron Yellow FeLithium Red Li2CO3
Magnesium White MgPotassium 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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PrelabRead 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
b. Octane
c. Iron
d. Iron (III) Chloride
e. Iron (II) Carbonate
f. Iron (II) Oxide6. 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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ProcedureCollect 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 (KClO3) and sugar.
Grind these two chemicals separately and place the powders in separate watch
glasses. Add about 2 mL of H2SO4 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 KClO3 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 KClO3. 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 KClO3 and sugar into an empty watch glass. Mix the powders gently
with the end of your spatula. Add one drop of H2SO4 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 (KClO3), 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. Any further explanation can be discussed in the body of your report.
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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 pageThe 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 completeThe 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. ResultsA. Experimental Procedures
1. Write a brief description of each experimenta. Zn + HClb. KClO3 +H2SO4
c. Sugar +H2SO4
d. KClO3 +Sugar + H2SO4
e. Roman Candle2. Include a diagram of experimental set-up, if you believe it would help.
B. Observational Results1. 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 +HCl1. Write the complete and balanced reaction involved2. 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 involvedb. 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. Write the complete and balanced reactions involvedb. Why is this equilibrium reaction driven to completion?c. 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.
4. Colorantsa. 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 spectrumd. What color did you observe?e. Discuss the difference between the color observed and emission
spectrum.
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