Kinetics of Hydrogen Peroxide

Kinetics of Hydrogen Peroxide

February 22, 2007

Chem. 1130

TA: Ms. Babcock

Room 1830 Chemistry Annex

PURPOSE OF THE EXPERIMENT

Kinetics of Hydrogen Peroxide

The major purpose of this experiment is to determine the rate law constant for the reaction of hydrogen peroxide and potassium iodide. In this experiment, the goal will be to try to measure the rate law constant at low acidity, since at low acidity, anything less than 1.0 x 10-3M, the effect of the hydrogen ion is negligible. To calculate the rate, the experiment will have to utilize the rate equation, which is expressed as Rate = k[H2O2]a[I-]b. At low acidity, the rate of the Hydrogen ion will not change, from our equation:

H2O2 (aq) + 2I- (aq) + 2H+ (aq) → I2 (aq) + 2H2O (l). Eqn. 1

If the rate in hydrogen does not change, it makes it easier to solve for the other rate constant. In this experiment, sodium thiosulfate will be added to suppress the rate of the reverse reaction. The objective is to measure the rate of the forward reaction. To do this, the rate of the reverse reaction must be eliminated. By using sodium thiosulfate accumulating Iodine on the left side and cause the reaction will be eliminated and it will cause the reaction to continue forward. Sodium thiosulfate will not react with any other compound in this solution, but will react rapidly and completely with iodine in the following way:

I2 (aq) + 2S2O32- → 2I- (aq) + S4O62- (aq) Eqn. 2

The rate constant can then be calculated from the forward reaction. This experiment will identify the rate constant from 5 solutions utilizing the above equation, only adding different concentrations of buffer, potassium iodide, starch, sodium thiosulfate, and hydrogen peroxide.

PROCEDURES TO BE USED

Kinetics of Hydrogen Peroxide

Before starting any step in this lab, five 250mL beakers must be obtained, cleaned, and dried. Also, this lab requires solutions of buffer, KI, starch, Na2S2O3, and H2O2. Other lab equipment to be used includes a stop watch and a thermometer.

After the beakers are cleaned, number the beakers one through five. Next, the five cleaned beakers will be used to prepare five different solutions from the following table:

Table: Concentrations for each solution in the experiment

Solution Number Buffer 0.300 M KI Starch 0.0200 M Na2S2O3 Water 0.100 M H2O2 Total Volume

1 5.00 1.50 1.00 5.00 82.50 5.00 100.00

2 5.00 3.00 1.00 5.00 81.00 5.00 100.00

3 5.00 5.00 1.00 5.00 79.00 5.00 100.00

4 5.00 5.00 1.00 5.00 74.00 10.00 100.00

5 5.00 5.00 1.00 5.00 64.00 20.00 100.00

Take the beaker labeled #1 and add the ingredients for Solution # 1 in this order: buffer, KI, starch, and Na2S2O3. However, it is important that the H2O2 is added last! To add the hydrogen peroxide, find another 250mL beaker, clean it out, and pour the required concentration into the beaker. Then, once the other ingredients are added into the beaker marked Solution # 1, add the concentration of H2O2 and begin the timer. Mix the solution in Solution # 1 by pouring it into the H2O2 beaker and then back from the H2O2 beaker to the Solution # 1 repeatedly until the solution is well mixed. Then put Solution #1 on a white piece of paper and once the solution changes color, stop the stopwatch and record the reaction time. Next, rinse out the H2O2 beaker thoroughly and set it aside to be used for later. It is recommended to move along and prepare the other solutions in their designated beakers by following the same procedure listed here.

When the data has been collected, calculate the initial rate of reaction, the initial concentrations of H2O2 and I-, determine the correct rate equation, and calculate the average rate constant for the reaction.

This lab experiment will be performed by two members who will work together to carry out this lab.

For better detailed procedures and instructions, refer to the Chemistry Lab Book:

Kinetics of Hydrogen Peroxide CHEM 1130 Spring Semester 2007 Lab Manual, Western Michigan University / Pages 1-3.

OBSERVATIONS AND DATA SHEETS

Kinetics of Hydrogen Peroxide

Once each of the five solutions are mixed, and the hydrogen peroxide is added, the member of the group keeping track of the time will start the timer. Once the timer starts, both group members are to watch for any reaction that occurs. The reaction should yield a slight change in color. The appearing color will be light blue. Once a reaction is noticeable, the timer is to stop the stopwatch and the group will record the time down in the following data table. If the color you observe is a dark blue, then you have passed the reaction point and you must start the experiment over.

The following data is the data that was collected in the lab. If you wish to see the calculations, please refer to the calculation Page that follows this section.

[H2O2]: 0.1 M

Table: Collected Data for Rate of Reaction of H2O2

Solution Number 1 2 3 4 5

Time of Color Change 2280 sec 1260 sec 800 sec 390 sec 185 sec

Start Time 0.0 sec 0.0 sec 0.0 sec 0.0 sec 0.0 sec

∆t in seconds 2280 sec 1260 sec 800 sec 390 sec 185 sec

Rate = ∆[ H2O2] / ∆t 2.193E-07 M/s 3.968E-07 M/s 6.250E-07 M/s 1.282E-06 M/s 2.703E-06 M/s

Initial [H2O2] 0.005 M 0.005 M 0.005 M 0.01 M 0.02 M

Initial [I-] 0.0045 M 0.0090 M 0.0150 M 0.0150 M 0.0150 M

The calculations performed in this lab included calculating the amount of sodium thiosulfate in each of the solutions, calculating the [H2O2] used up during the reaction in each solution, calculating the initial