H2O2 - Lab PDF

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KINETICS OF H2O2 DECOMPOSITION

Kinetics of the Decomposition of Hydrogen Peroxide Tulsa Community College

KINETICS OF H2O2 DECOMPOSITION

PURPOSE: To conduct the catalyzed decomposition of hydrogen peroxide, calculate the rate constant, determine the rate law expression, and calculate the activation energy. PRE LAB QUESTIONS: Part I II III IV

Volume H2O2 (mL) 4 4 4 4

[H2O2] before mixing 0.9 M 0.9 M 0.4 M 0.9 M

Volume KI (mL) 1 1 1 1

[KI] before mixing 0.50 M 0.25 M 0.50 M 0.50 M

Calculating the molarity of a 3% H2O2 solution 3 g H2O2 in 100 mL solution or 30 g/1 L 30 g H2O2/34 g/mol = 0.88 mol 0.88 mol/1 L = 0.88 M or 0.9 M Calculating the molarity of 1.5% H2O2 solution 1.5 g H2O2 in 100 mL solution or 15 g/1 L 15 g H2O2/34 g/mol = 0.44 mol 0.44 mol/1 L = 0.44 M or 0.4 M PROCEDURE: Set up a water bath and record its temperature. Measure out 4 mL of 3% H2O2 solution into a test tube and add the mini magnetic stir bar then seal it with a solid rubber stopper. Place the test tube into the water bath and turn on the stirrer. Measure out 2 mL of 0.5 M KI solution into 10.0 mL graduated cylinder then draw about 1 mL of the KI solution into a graduated Beral pipet. Invert the pipet and immerse the reservoir end of the pipet in the water bath. Connect a Gas Pressure Sensor to channel 1 of the Veriner computer interface then connect it to the computer. Connect the one-hole rubber stopper to the sensor. Open “12

KINETICS OF H2O2 DECOMPOSITION

Peroxide” on Logger Pro. Remove the test tube from the water bath and remove the solid stopper. Quickly transfer 1 mL of KI solution into the test tube. Reseal the test tube and place it back into the water. Click “collect” and wait 3 minutes. After the data collection is complete, remove the stopper from the test tube to relieve the pressure. Select a linear region on your graph just after the initial plateau that covers about one minute. Click on the Linear Regression button to calculate the best-fit line equation. Record the slope as the initial rate of the reaction. Rinse and dry the test tube with a paper towel. Measure out 4 mL of 3% H2O2 solution into a test tube and add the mini magnetic stir bar then seal it with a solid rubber stopper. Place the test tube into the water bath. Add 1 ML of distilled water to the remaining 1 mL of KI solution and mix the solution. Draw about 1 mL of the KI solution into a plastic Beral pipet. Invert the pipet and immerse the reservoir end of the pipet in the water bath. Wait 2 minutes. Remove the test tube from the water bath and remove the solid stopper. Quickly transfer 1 mL of KI solution into the test tube. Reseal the test tube and place it back into the water. Click “collect” and wait 3 minutes. After the data collection is complete, remove the stopper from the test tube to relieve the pressure. Select a linear region on your graph just after the initial plateau that covers about one minute. Click on the Linear Regression button to calculate the best-fit line equation. Record the slope as the initial rate of the reaction. Rinse and dry the test tube with a paper towel. Prepare a 1.5% H2O2 solution by mixing 2 mL of distilled water with 2 mL of 3% H2O2. Transfer it to the test tube and seal it with a solid stopper. Place the tube in the water bath. Rinse and clean the graduated cylinder that was used for the KI solution. Add a fresh 2 mL of 0.5

KINETICS OF H2O2 DECOMPOSITION

M KI solution to it. Draw about 1 mL of the KI solution into a plastic Beral pipet. Invert the pipet and immerse the reservoir end of the pipet in the water bath. Wait 2 minutes. Remove the test tube from the water bath and remove the solid stopper. Quickly transfer 1 mL of KI solution into the test tube. Reseal the test tube and place it back into the water. Click “collect” and wait 3 minutes. After the data collection is complete, remove the stopper from the test tube to relieve the pressure. Select a linear region on your graph just after the initial plateau that covers about one minute. Click on the Linear Regression button to calculate the best-fit line equation. Record the slope as the initial rate of the reaction. Rinse and dry the test tube with a paper towel. Set up a water bath at 30°C. Measure out 4 mL of 3% H2O2 solution into a test tube and add the mini magnetic stir bar then seal it with a solid rubber stopper. Place the test tube into the water bath and turn on the stirrer. Draw about 1 mL of the KI solution into a graduated Beral pipet. Invert the pipet and immerse the reservoir end of the pipet in the water bath. Wait 2 minutes. Remove the test tube from the water bath and remove the solid stopper. Quickly transfer 1 mL of KI solution into the test tube. Reseal the test tube and place it back into the water. Click “collect” and wait 3 minutes. After the data collection is complete, remove the stopper from the test tube to relieve the pressure. Select a linear region on your graph just after the initial plateau that covers about one minute. Click on the Linear Regression button to calculate the best-fit line equation. Record the slope as the initial rate of the reaction. Rinse and dry the test tube with a paper towel.

KINETICS OF H2O2 DECOMPOSITION

CHEMICALS USED: •

H2O

•

H2O2

•

KI

DATA: Par t

Reactants

Temperature (°C)

I II

4 mL 3.0% H2O2 + 1 mL 0.5 M KI 4 mL 3.0% H2O2 + 1 mL 0.25 M KI 4 mL 3.0% H2O2 + 1 mL 0.5 M KI 4 mL 3.0% H2O2 + 1 mL 0.5 M KI

24.3°C 24.3°C

Initial Rate (kPa/s) 0.3347 0.1516

24.3°C 33.6°C

0.1548 0.5554

III IV

Par Initial rate t (mol/L-s) I 1.35 X 10-4 II 6.13 X 10–5 III 6.26 X 10-5 IV 2.17 X 10-4 CONCLUSIONS:

[H2O2] after mixing 0.704 M 0.704 M 0.352 M 0.704 M

[I-] after mixing 0.1 M 0.05 M 0.1 M 0.1 M

Rate constant k 3.5 X 10-3 3.5 X 10-3 5.6 X 10-3 5.6 X 10-3

The rate law expression for this experiment is k[H2O2]1.8[KI]1.14. The first step is the rate determining step because it creates IO-, which is used up in the second step. The activation energy for this experiment is 38299.69. POST LAB QUESTIONS: 1. Determine the order of the reaction in H2O2 and KI. Explain how you arrived at your answer. Calculate the rate constant, k, and write the rate law expression for the catalyzed

KINETICS OF H2O2 DECOMPOSITION

decomposition of hydrogen peroxide. To convert the rate from kPa/s to M/s use the ideal gas equation, M = P/RT where R, is the gas constant = 8.314 L X kPa X K-1 X mol –1 I. Initial rate 0.3347 kPa/s divided by (8.314 X 297.3 K) = 1.35 X 10-4 1.35 X 10–4 = k[0.704 H2O2]1.8[0.1 KI]1.14 (1.35 X 10 –4/3.85 X 10-2) = k(3.85 X 10-2/3.85 X 10-2) 3.5 X 10-3 = k II. Initial rate 0.1516 kPa/s divided by (8.314 X 297.3 K) = 6.13 X 10-5 6.13 X 10–5 = k[0.704 H2O2]1.8[0.05 KI]1.14 (6.13 X 10–5/1.74 X 10-2) = k(1.74 X 10-2/1.74 X 10-2) 3.5 X 10-3 = k III. Initial rate 0.1548 kPa/s divided by (8.314 X 297.3 K) = 6.26 X 10-5 6.26 X 10-5 = k[0.352 H2O2]1.8[0.1 KI]1.14 (6.26 X 10-5/1.1 X 10-2) = k(1.1 X 10-2/1.1 X 10-2) 5.6 X 10-3 = k IV. Initial rate 0.5554 kPa/s divided by (8.314 X 306.6 K) = 2.17 X 10-4 2.17 X 10-4 = k[0.704 H2O2]1.8[0.1 KI]1.14 (2.17 X 10-4/3.85 X 10-2) = k(3.85 X 10-2/3.85 X 10-2) 5.6 X 10-4 = k 2. The following mechanism has been proposed for this reaction: H2O2 + I- → IO- + H2O H2O2 + IO- → I- + H2O + O2 If this mechanism is correct, which step must be the rate-determining step? Explain. The first step is the rate-determining step because it creates IO-, which is used up in the second step.

KINETICS OF H2O2 DECOMPOSITION

3. Use the Arrhenius equation (shown below) to determine the activation energy, Ea, for this reaction. Show your calculations. Ln (k1/k2) = (Ea/R)((1/T2)-(1/T1)) where value of gas constant R = 8.314 J/mol X K Ln (3.5 X 10-3/5.6 X 10-3) = (Ea/8.314)((1/306.6)-(1/297.3)) (-0.47/-1.02 X 10-4) = (Ea/8.314)(-1.02 X 10-4)/(-1.02 X 10-4) 8.314(4606.65) = (Ea/8.314)8.314 38299.69 = Ea...