Good Example Of Measuring The Heat Of Decomposition Of Hydrogen Peroxide Report

Introduction

This experiment has two aims. The first aim was to investigate the effect of the type of calorimeter on the temperature change recorded when hot and cold water is mixed. In the second aim, the experiment sought to investigate how the type of a catalyst affects the reaction. The experiment was divided into two main parts: week 1 and week 2. Week 1 was further divided into two parts: part1 and part 2. Part 1 sought to determine the calorimeter constant. On the other hand, part 2 sought to measure the heat of decomposition of hydrogen peroxide. The research questions investigated in this experiment include the following: what is the calorimeter constant of the calorimeter made of Styrofoam cup and that made of a two beakers with paper towels between them? What is the heat of decomposition of hydrogen peroxide? How does the type of calorimeter affect the temperature change when hot water is mixed with cold water? How does the type of a catalyst affect the decomposition reaction of hydrogen peroxide?
Two hypotheses were formed at the beginning of the experiment. First, the group hypothesized that Potassium iodide speeds up the rate of decomposition of hydrogen peroxide faster than yeast. Second, the group hypothesized that Styrofoam cup is a more effective calorimeter than two beakers with paper towels between them.
In the first aim, the independent variable was the type of calorimeter while the dependent variable was change in temperature. On the other hand, in the second aim, the independent variable was the type of catalyst while the independent variable was the time taken for the reaction to complete.

No changes were made to the handout.

Methods
This experiment was performed in two main steps that took two weeks altogether. In week 1, the students sought to determine the calorimeter constant and the heat of decomposition of hydrogen peroxide. This step was divided into two parts: part 1 and part 2.

Part 1

First, the Lab Quest Unit was turned on and the temperature probe plugged in. one Styrofoam cup was then stacked inside another. Two pieces of aluminum foil large enough to wrap over the top of the cup were torn and wrapped over the stack of cups and used as one of the calorimeters.
200mL of DI water was measured in a large beaker. The temperature of the water was measured and recorded as the initial temperature of the cold water and the calorimeter. 25mL of the cold water was then measured with a graduated cylinder and poured into the top cup of one of the calorimeters. The step was repeated for the other calorimeter. 25mL of hot water was poured into the graduated cylinder and its temperature recorded. The temperature probe was then placed into the cold water solution in the calorimeter. The group began recording the temperature of the water inside the calorimeter by pressing the arrow at the bottom of the Lab Quest screen. The 25mL of hot water was then poured immediately into the colorimeter containing water at room temperature. The cup was covered immediately with aluminum foil. The cup was swirled periodically in order to mix the water. The group stopped recording the temperature probe immediately the temperature began declining. Temperature and time data from the LabQuest was then entered to the excel spreadsheet for the experiment. The calorimeter constant for each calorimeter was then determined using the equations contained in the appendix of the handout. The experiment was repeated for each calorimeter two more times.

Part 2

250mL of H2O2 solution was obtained and its temperature measured. The temperature was recorded as the initial temperature of the solution and the initial temperature of the calorimeter. The concentration of H2O2 solution was also recorded. 60 mL of 0.5 M Fe (NO3)3 solution was obtained. 40.0 mL of H2O2 solution was measured in a graduated cylinder and poured into a calorimeter. The Lab Quest unit was turned on and the temperature probe plugged in. 10.0 mL of Fe(NO3)3 solution was measured in another graduated cylinder and then poured into the calorimeter. The calorimeter was then covered immediately with the foil lead and the temperature probe inserted through the hole in the lid. Meanwhile, the students began recording the temperature of the solution. The solution was swirled periodically to mix the solution. The students stopped recording the temperature probe immediately the temperature started declining. Temperature and time data from the LabQuest to the Excel spreadsheet for this experiment were entered in an excel spread sheet. The equations contained in the appendix of the handout were then used to calculate the heat of decomposition of the H2O2 solution. The calorimeter was then rinsed out and dried using a paper towel. The procedure was repeated for each calorimeter two more times.
In order to investigate the first aim, part 1 was repeated using two different calorimeters: calorimeter made of Styrofoam cup and that made of a two beakers with paper towels between them. The students then obtained 10mL of yeast and 10mL of potassium iodide solutions. Each solution was then mixed with H2O2 solution and the reaction timed from the start of the solution to the point when the temperature began to decline.

Data

Part 1: Determine Calorimeter Constant
Calorimeter #1 Trial 1 Trial 2 Trial 3
Initial cold water temp 24.0ºC 24.0ºC 24.3ºC
Initial hot water temp 60.0ºC 56.7ºC 52.7ºC
Final water temp 40.99ºC 39.44ºC 38.47ºC
Cold water T (final - initial) 16.44ºC 10.44ºC 14.17
Hot water T (final - initial) -19.01ºC -17.26ºC -14.23ºC

Cold water mass 25g 25g 25g

Hot water mass 24.5g 24.5g 24.5g
Value of Ccal (include units) 2.52J/ºC 1.82J/ºC 0.11J/ºC

Average value of Ccal 1.48J/ºC

Part 2: Measure Hrxn for the Decomposition of Hydrogen Peroxide
Calorimeter #1 Trial 1 Trial 2 Trial 3
Average value of Ccal 1.48J/ºC 1.48J/ºC 1.48J/ºC
Initial solution temp 22.9ºC 22.8ºC 22.3ºC
Final solution temp 37.6ºC 37.4ºC 37.1ºC

Solution mass 50g 50g 50g

Value of Hrxn (J) -3096.906 -3075.928 -3118.064
Concentration of H2O2 0.881 0.881 0.881
Value of Hrxn (J/mol) -2382.3 -2366.1 -2398.5

Average value of Hrxn (J/mol) -2382.3

Part 1: Determine Calorimeter Constant
Calorimeter #2 Trial 1 Trial 2 Trial 3
Initial cold water temp 21.7ºC 21.8ºC 23.5ºC
Initial hot water temp 53.3ºC 52.1ºC 58.5ºC
Final water temp 37.43ºC 36.38ºC 90.84ºC
Cold water T (final - initial) 15.73ºC 14.58ºC 8.34ºC
Hot water T (final - initial) -15.87ºC -15.72ºC -17.66ºC

Cold water mass 25g 25g 25g

Hot water mass 24.5g 24.5g 24.5g
Value of Ccal (include units) 0.19/ºC 1.14J/ºC 9.32J/ºC

Average value of Ccal 3.49J/ºC

Part 2: Measure Hrxn for the Decomposition of Hydrogen Peroxide
Calorimeter #2 Trial 1 Trial 2 Trial 3
Average value of Ccal 3.49J/ºC 3.49J/ºC 3.49J/ºC
Initial solution temp 22.4ºC 23.0ºC 23.0ºC
Final solution temp 37.5ºC 27.1ºC 37.3ºC

Solution mass 50g 50g 50g

Value of Hrxn (J) -3105.224 -2998.929 -3041.467
Concentration of H2O2 0.881 0.881 0.881
Value of Hrxn (J/mol) -1001.7 -967.4 -981.1

Average value of Hrxn (J/mol) -483.4

Calorimeter #2 Trial 1 Trial 2 Trial 3
Initial cold water temp 24.7ºC 22.5ºC 26.9ºC
Initial hot water temp 51.4ºC 51.1ºC 52.6ºC
Final water temp 34.2ºC 34.4ºC 36.8ºC
Cold water T (final - initial) 9.5ºC 11.9ºC 9.9ºC
Hot water T (final - initial) -17.2ºC -16.7ºC -15.8ºC
Cold water mass 25g 25g 25g

Hot water mass 25g 25g 25g

Value of Ccal (include units) 84.78J/ºC 42.31J/ºC 62.33J/ºC

Average value of Ccal 63.14J/ºC

Calorimeter #2 Trial 1 Trial 2 Trial 3
Initial cold water temp 22ºC 22.6ºC 26.3ºC
Initial hot water temp 51.1ºC 50.9ºC 52.5ºC
Final water temp 35.7ºC 35.5ºC 36.5ºC
Cold water T (final - initial) 13.7ºC 12.9ºC 10.2ºC
Hot water T (final - initial) -15.4ºC -15.3ºC -16ºC
Cold water mass 25g 25g 25g

Hot water mass 25g 25g 25g

Value of Ccal (include units) 92.58J/ºC 19.46J/ºC 59.48

Average value of Ccal 57.17J/ºC

Figure 7: Data for the decomposition of H2O2 in the presence of KI in question 1 of the week 2 experiment
Figure 8: Data for the decomposition of H2O2 in the presence of Yeast in question 1 of the week 2 experiment

Discussion

Data from the experiment show that the calorimeter constant for Styrofoam cup calorimeter is 63.14J/ºC while that of two beakers with paper towels between them is 57.17J/ºC. These data mean that more heat energy should be absorbed by the Styrofoam cup calorimeter in order to raise its temperature by the same value as the two beakers with paper towels between them. Consequently, the two-beakers with paper towels between them is a more effective calorimeter since the amount of heat it absorbs is likely to be detected more easily than the Styrofoam cup calorimeter. Therefore, the second hypothesis is rejected.
The experiment further found that when yeast was used, decomposition of H2O2 solution took an average of 103.5 seconds. On the other hand, the reaction took an average of 462 second to complete when KI was used as a catalyst. Therefore, the experiment indicates that yeast speeds up the decomposition of H2O2 faster than KI. Therefore, the first hypothesis is rejected.
The various values recorded in the experiment varied widely from one another due to error. The various sources of error in the experiment include the loss of heat during the mixing of water. The heat lost could have not been easily accounted for.

Conclusion

The experiment was successful as the students learnt much. In addition, the students had a good experience during the experiment.