Measuring The Heat of Decomposition of Hydrogen Peroxide

Project description
It is an experiment divided in 2 part

1st week and 2nd week

Done by 4 students

Group A (my group) & Group B

All the details, procedures, data sheets, data calculations, excel data sheet will be attached to the order.

Please follow exactly the instructions in the handouts and writing report guideline

Report should include all the calculations in details, graphs, tables and any needed information

The data for the both group should be included and made the comparison between results.

Hypothesis should be approved in this experiment.

Report should include; introduction, objectives, materials and method results, results discussion, conclusion and any other needed information

If there is anything not clear please ask and please follow the instructions carefully

Background

Hydrogen peroxide (H2O2) is a chemical that you can purchase for use as an antiseptic, hair bleach or even swimming pool disinfectant. All these products rely on

hydrogen peroxide reacting with a chemical in an oxidation-reduction (redox) reaction. Hydrogen peroxide is reduced to water and the other chemical is oxidized.

Oxidizing the molecules that are part of a bacteria cell can cause the cell the die, making H2O2 a good antiseptic and water disinfectant. When oxidizing natural dyes

in hair, H2O2can decompose those molecules into colorless products.

Hydrogen peroxide is so good at oxidizing molecules that it will oxidize itself in the reaction:

2 H2O2 (aq) → 2 H2O (l) + O2 (g) Reaction 1

Of course, some of the oxygen in the hydrogen peroxide molecule is reduced also.

This reaction is slow and any commercial product containing H2O2 will also contain stabilizers, making the reaction even slower. A typical H2O2 solution can be stable

for several years. However, there are other chemicals, called catalysts, which make Reaction 1 occur faster.For instance, you might see bubbles form when you apply

hydrogen peroxide on a cut to disinfect the wound. A chemical in blood, an enzyme called catalase, is a catalyst thatquickly converts hydrogen peroxide to water and

oxygen gas. Your liver also contains catalysts that remove hydrogen peroxide from your body (some cells naturally produce H2O2 but it is poisonous in high

concentrations). An entertaining example of Reaction 1 is the Elephant’s Toothpaste demonstration in which H2O2, a catalyst (potassium iodide, KI) and dish detergent

are mixed together. You can view this demonstration at:
http://www.imaginationstationtoledo.org/content/2011/03/supersized-elephants-toothpaste/
(Your experiments will be more similar to the first demonstration but without adding soap.)

Reaction 1 releases heat (exothermic) when hydrogen peroxide becomes water and oxygen gas. Regardless of how fast it occurs, the total amount of heat released by

Reaction 1 will be the same. A fast decomposition of H2O2 would simply release the heat faster but it would be the same amount of heat released by a slow

reaction.Measuring the heat involved in a reaction is called calorimetry.More detailed information about calorimetry is found in chapter 6 of your textbook and in the

Appendix contained in this handout.

In this two-week laboratory experiment, you will measure the change in enthalpy (Hrxn) when hydrogen peroxide decomposes. The goals for the first week of this

experiment are:

•   Measure the temperature change of a H2O2 solution as the hydrogen peroxide decomposes.
•   Measure the amount of heat that is absorbed by the container (calorimeter) during the reaction.
•   Use this information to determine the calorimeter constant and the enthalpy change of the reaction.

Skill Building Exercises

Your team will perform two skill building exercises. First, you will determine the values of the calorimeter constants for two calorimeters. You will use these

calorimeters in the second skill building exercise when you measure the enthalpy change for the decomposition of hydrogen peroxide. These activities will prepare you

to perform more in-depth experiments next week. You will record your data on a Data Sheet to be turned in to your GSA before you leave.

Part 1: Determine Calorimeter Constant
Your team is given four Styrofoam cups and some aluminum foil to make two calorimeters. You will measure equal volumes of hot water and room temperature water then

mix them together in the calorimeter. Measure the temperature of each portion of water before mixing and then after mixing. Repeat this process three times for each

calorimeter to determine the values of the calorimeter constants. Your team can perform these experiments for both calorimeters at the same time to save time. One or

two teammates can work efficiently with one calorimeter.

Safety Note: The surface of a hot plate can get very hot, even if the water being heating is not very hot. Keep flammable materials such as paper away from the hot

plate. Measure the temperature of the water before trying to pick up the beaker of hot water. If your water gets too hot, ask the stockroom for beaker tongs to help

you safely remove the hot beaker. Set it on the benchtop so that it can cool. If you see any spilled water on the floor, clean it up so that somebody does not slip.

Perform these steps for each calorimeter. Your team can perform the procedure for the two calorimeters at the same time. One or two students can use each

calorimeter.

1. Turn on the Lab Quest unit and plug in the temperature probe.
2. Stack one Styrofoam cup inside another. Carefully tear two pieces of aluminum foil large enough to wrap over the top of the cup. Wrap the piece over the top

of the stack of cups. This will be one of your calorimeters. Make a notation of #1 or #2 on it so that you don’t get the two calorimeters mixed up.
3. Measure 200 mL of DI water in a large beaker. Measure the temperature of the water. This will be the initial temperature of the calorimeter and the initial

temperature of the “cold” water. The entire team can use this 200 mL of DI water.
4. Measure 25.0 mL of the cold water using the graduated cylinder and pour into the top cup of a calorimeter. Repeat this for the other calorimeter.
5. Measure 25.0 mL of hot water from the beaker on the large hot plate in the hood. The temperature should be between 50 and 60 °C.Measure the temperature of the

hot water after you pour it into the graduated cylinder.
6. Place the temperature probe into the cold water solution in the calorimeter. Begin recording the temperature of the water inside the calorimeter by pressing

the green arrow at the bottom of the Lab Quest screen.
7.   Immediately pour the 25.0 mL of hot water into the calorimeter containing room temperature water.
8.   Quickly cover the cup with the aluminum foil.
9.   Periodically swirl the cups so that the water mixes.
10.   Once the temperature begins to decline for several minutes, stop recording the temperature probe and disassemble the calorimeter. Pour the used water in the

sink.
11. Enter temperature and time data from the LabQuest to the Excel spreadsheet for this experiment. This will calculate the temperature change that occurred.
12. Use the equations presented in the Appendix of this handout to determine the calorimeter constant for each calorimeter. Record these values on your data

sheet. Show your calculations on the data sheet also.
13. Dry the inside of the calorimeter with a paper towel.
14. Repeat this procedure for each calorimeter two more times so that you have three calorimeter constant values for each calorimeter. Calculate an average value

for each calorimeter.

You might want to write the average value of the calorimeter constant on the outside of the Styrofoam cups of the calorimeter.

Part 2: Measure Hrxn for the Decomposition of Hydrogen Peroxide

In this exercise, you will mix a solution of hydrogen peroxide with a solution of iron (III) nitrate which speeds up (catalyzes) the H2O2 decomposition reaction. As

you did in Part 1, you will measure the initial and final temperatures of the solution. Use the equations in the Appendix and the calorimeter constant values that you

calculated in Part 1 to determine Hrxn for the reaction,

2 H2O2 (aq) → 2 H2O (l) + O2 (g) Reaction 1

Safety Note: The hydrogen peroxide solution you are using is approximately 3% H2O2 by volume, which is the same concentration as the kind you use for disinfecting

cuts. If you spill H2O2 solution on your skin, wash with lots of water. It may sting if you have any cuts.

1. Each team should obtain about 250 mL of H2O2 solution. Do not get more than this amount since the amount of solution available for your class is limited.

This will be enough for all the experiments you perform in Part 2.
2. Measure the temperature of the H2O2 solution. This is the initial temperature of the solution and the initial temperature of the calorimeter. Note the

concentration of H2O2 on the container. Record the initial temperature and the concentration on your data sheet.
3. Each team should obtain about 60 mL of 0.5 M Fe(NO3)3 solution.

Perform the rest of the steps for each calorimeter. Your team can perform the procedure for the two calorimeters at the same time. One or two students can use each

calorimeter.

4.   Measure 40.0 mL of H2O2 solution in a graduated cylinder. Pour this solution into a calorimeter.
5.   Turn on the Lab Quest unit and plug in the temperature probe.
6.   Measure 10.0 mL of Fe(NO3)3 solution in another graduated cylinder.
7.   Pour the Fe(NO3)3 solution into the calorimeter. [Note:Be ready to perform step 8 because the reaction will begin immediately after adding the Fe(NO3)3

solution.]
8. Quickly cover the calorimeter with the foil lid and insert the temperature probe through the hole in the foil that you made earlier.
9. At the same time that you add the Fe(NO3)3 solution, begin recording the temperature of the solution inside the calorimeter by pressing the green arrow at the

bottom of the Lab Quest screen.
10. Periodically swirl the cups so that the solution mixes.
11. Once the temperature begins to decline for several minutes, stop recording the temperature probe and disassemble the calorimeter. Pour the solution in the

waste container.
12. Enter temperature and time data from the LabQuest to the Excel spreadsheet for this experiment. This will calculate the temperature change that occurred.
13. Use the equations presented in the Appendix of this handout and your calorimeter constant from Part 1 to determine the value of Hrxn. Record these values on

your data sheet. Show your calculations on the data sheet also.
14. Rinse out the calorimeter and dry the inside of the calorimeter with a paper towel.
15. Repeat this procedure for each calorimeter two more times so that you have three Hrxn values for each calorimeter. Calculate an average value of Hrxn using

all six values.
16. Clean up your work area. Clean off the temperature probe with a damp paper towel. Return all the Lab Quest equipment to the stockroom. Keep your

calorimeters in your drawer for next week.

Possible Research Options for Lab Experiment Week 2

Based on the preliminary work you did in the skill-building portion of this experiment, there are several areas for investigation. You will choose TWO of these areas

before you leave lab on the day of the skill-building exercise and report it to your GSA. During week 1 and 2 of the experiment, you will meet with your team members

to write hypothesis statements for two of the research questions your team chose and to develop a method for testing each hypothesis. This includes determining

appropriate variables (independent, dependent, and control). As a reminder, a hypothesis is a testable generalization which states the relationship between two

selected variables under specified conditions. An independent variable is what is changed in order to do your experiment. A dependent variable depends on the outcome

of the independent variable. For example, if you were determining the growth rate of a plant when exposed to different amounts of light, the light duration would be

the independent variable, whereas the growth rate itself is the dependent variable. Control variables are variables put in to control the system. For example, in

the plant growth rate experiment, a control variable might be the addition of a set amount of water supplied to all plants during the experimentation process.

Here are several research options for this particular experiment. You should be able to complete enough experiments for two of them if you use both

calorimeters and your team divides the work evenly among the team members. Remember that you only have one week to complete this work.

1) How does the type of calorimeter affect the temperature change when mixing hot and cold water? You will determine Ccal for different calorimeters using the

procedure described in Part 1. You will then determine which is most effective (you can decide what “effective” means). Possible calorimeters include: one Styrofoam

cup, two beakers with paper towels between them, a coffee cup and thermos.

2) How does the particular catalyst affect the reaction? You will perform the H2O2 decomposition reaction using two different catalysts: yeast and potassium

iodide. You will use 10 mL of each catalyst solution including 0.5 g of yeast and a 0.5 M solution of KI. Determine which catalyst causes the fastest reaction per

mole or per gram. (See the video mentioned in the Background section for information about preparing the yeast.)

3) What is the minimum concentration of Fe(NO3)3 catalyst needed for the reaction of H2O2to be completed within 5 minutes? You will repeat the perform the

procedure described in part 2 but using different concentrations of Fe(NO3)3 solution.

Appendix: Deriving Calorimetry Equations

The amount of heat involved in a reaction is represented by qrxn. When heat is released, q has a negative value (q < 0) and when heat is absorbed, q is positive (q >

0). The amount of heat that is released has to go somewhere – it can’t disappear. For this reaction, the heat is absorbed by the solution and the container. The

amount of heat released is equal to the amount of heat absorbed by the water and container but has the opposite sign. That means,

– qrxn = qsoln + qcontainer Equation 1

Chemists are interested in discovering the amount of heat involved in a reaction. To do this, they measure the heat absorbed by the solution and the container then

use Equation 1 to calculate qrxn. If you are measuring heat involved in a reaction, the container is called a calorimeter. The metric unit of heat is the Joule,

abbreviated as J. If a calorimeter absorbs 10 J of heat and the solution absorbs 35 J of heat, then,

– qrxn = 35 J + 10 J

qrxn = – 45 J

Since our container is more properly called a calorimeter, qcontainer will be replaced by qcal. How would a chemist measure the amounts of energy absorbed by a

solution and a calorimeter? When a reaction releases heat, the amount of heat absorbed by a solution is equal to the mass of the solution (msoln), the change in

temperature of the solution (Tsoln= Tfinal – Tinitial) and a constant, called the solution’s specific heat (ssoln). For aqueous solutions, ssoln = 4.184 J .

That means: g °C

qsoln = msolnssolnTsoln Equation 2

Both the mass and change in temperature can be measured in an experiment. Instead of weighing a cup of water, measure the volume of solution and convert it to mass.

Look up the density of water at that temperature.

The heat absorbed by a calorimeter is determined without performing any chemical reaction. Instead, hot and cold water are mixed together in the calorimeter. Heat

released as hot water cools is absorbed by the cold water and the calorimeter. The amount of heat absorbed by the calorimeter depends on the calorimeter constant

(Ccal) and the temperature change of the calorimeter (Tcal). The calorimeter changes temperature because it is absorbing heat from the hot water. Since q is

negative when heat is released and q is positive when heat is absorbed, then,

– qhot = qcold + qcal Equation 3

and,

– qhot = qcold + CcalTcal Equation 4

Using Equation 2 to determine the values of qhot and qcold, Equation 4 becomes,

– mhot shotThot = mcold scoldTcold + CcalTcold Equation 5

This equation becomes easier to work with under the following conditions:
•   The specific heat values of hot water and cold water are the same (shot = scold = s)
•   We use the same mass of hot water and cold water.
•   The initial temperature of the cold water and calorimeter will be the same
•   The final temperature of the calorimeter, hot water and cold water will be the same because they are mixed together.

That means,

– mhot s (Tfinal – Tinitialhot) = mcold s (Tfinal – Tinitial cold) + Ccal (Tfinal – Tinitialcold) Equation 6

While this is a long equation, every single value is something you can measure, except Ccal. That is what you will calculate after measuring the temperature change as

you mix hot and cold water. The calorimeter constant Ccal is unique for each calorimeter but its value does not depend on the reaction that occurs in the calorimeter.

For a particular calorimeter, Ccalhas the same value when mixing hot and cold water, when decomposing hydrogen peroxide or performing any other reaction.

Returning to Equation 1, we can now substitute equations for the heat absorbed by the solution and calorimeter, based on what we have worked out here:

– qrxn = msolnssolnTsoln + CcalTcal Equation 7

There is one last modification needed. Since this reaction is performed at constant pressure (the calorimeter allows the oxygen gas to escape), we can replace the

symbol q with H, which is the enthalpy change for the reaction.

– Hrxn = msolnssolnTsoln + CcalTcal Equation 8

This is the equation you will use to determine the enthalpy change for the decomposition of hydrogen peroxide. You will use Equation 6 to determine the calorimeter

constant that you will use in Equation 8.

Data Sheet for Experiment 4

Names

Team # ______ Section___________ Date

Part 1: Determine Calorimeter Constant

Calorimeter #1 Trial 1 Trial 2 Trial 3
initial cold water temp
initial hot water temp
final water temp
cold water T (final – initial)
hot water T (final – initial)
cold water mass
hot water mass
value of Ccal (include units)
Show your work on a separate sheetfor one calculation.
average value of Ccal

Part 2: Measure Hrxn for the Decomposition of Hydrogen Peroxide

Calorimeter #1 Trial 1 Trial 2 Trial 3
average value of Ccal
initial solution temp
final solution temp
solution mass
value of Hrxn (J)
Show your work on a separate sheet for one calculation.
concentration of H2O2
value of Hrxn (J/mol)
Show your work on a separate sheet for one calculation.
average value of Hrxn (J/mol)

Part 1: Determine Calorimeter Constant

Calorimeter #2 Trial 1 Trial 2 Trial 3
initial cold water temp
initial hot water temp
final water temp
cold water T (final – initial)
hot water T (final – initial)
cold water mass
hot water mass
value of Ccal (include units)
Show your work on a separate sheet
for one calculation.
average value of Ccal

Part 2: Measure Hrxn for the Decomposition of Hydrogen Peroxide

Calorimeter #2 Trial 1 Trial 2 Trial 3
average value of Ccal
initial solution temp
final solution temp
solution mass
value of Hrxn (J)
concentration of H2O2
value of Hrxn (J/mol)

average value of Hrxn (J/mol)

Team Role Assignments and Research Option Choice for Experiment 4

Manager

Chemist

Instrument Technician

Software Technician

In one or two sentences, state your two research options that you will investigate during the next week. Be as specific as possible. Your GSA may ask you revise your

option if other teams have already chosen the same option.

Method or Plan of Investigation for Experiment 4
(Make a copy to turn in to GSA at the beginning of 2nd week)

Names _____________________________________________ Section # _________

Hypothesis Statement:

Procedure (in outline form):

Topics for your results section:
Present your results in organized tables, figures, and/or graphs so that they are easy for your GSA to understand. Prepare graphs using a spreadsheet program like

Excel or Open Office. Label your graph axes and write a title for each graph, figure or table. Do not prepare your graphs by hand on graph paper.

If you use an equation for calculating your results, define the variables in the equation and use correct significant figures.

Write about your results in sentences and paragraphs. Explain what is important about your graphs, tables and figures of data. You do not need to explain every

single result. Summarize your results so that your GSA can understand the work that you did.

Topics for your discussion section:
Write a clear, scientific statement about the purpose of your research and the research question your team is investigating.

Write a hypothesis statement. Your hypothesis should be a testable generalization which states the relationship between two selected variables under specified

conditions. It is OK if your hypothesis statement turns out to be wrong – that is a part of research.

Define your independent, dependent, and control variables.

In three or four sentences, briefly explain how you modified the experiment handout procedure in order to complete your research.

Explain how your results support or do not support your hypothesis.

Discuss any limitations of your experimentor mistakes you made and how they affect the final results. Be specific – do not simply blame everything on “Human Error.”

Recommend reasonable suggestions for improving the experiment. Think about what you would do differently if you could repeat your experiment.

Topics for your reflection section:
Explain your individual contribution to your lab group’s effort during the lab session and explain how effectively you and your lab partner(s) worked together

throughout the experiment.

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