Kinetics: Decomposition of Hydrogen Peroxide catalyzed by Iodide

Computer-Interfaced Experiments - Temperature Measurement
Kinetics
Decomposition of Hydrogen Peroxide catalyzed by Potassium Iodide

Objective: Dependance of the Reaction Rate upon the Concentration of the Catalyst

Peter Keusch

Datalogging and data analysis using the Program CHEMEX and the Analog-Digital-Converter CHEMBOX
IBK electronic + informatic

German version

Chemicals:
0.43 M aqueous potassium iodide solution
hydrogen peroxide 10 %

0.1075, 0.215 and 0.3225 molar iodide solutions are prepared by diluting appropriate aliquots of the 0.43 molar stock potassium iodide solution.

Apparatus and glass wares:
magnetic stirring bar
stirring bar remover
Dewar vessel (500 mL) with plastic cover, suitable for magnetic stirrer
temperature sensor<
volumetric pipet 8 mL, 25 mL, 50 mL
disposal container

Hazards and safety precautions:

Inhalation of potassium iodide dust may irritate respiratory tract. May act as a skin or eye irritant. May cause sensitization or allergic reaction.

Hydrogenperoxide is toxic, corrosive - can cause serious burns. Eye contact can cause serious injury, possibly blindness. Harmful by inhalation, ingestion and skin contact.

Safety glasses and gloves, suitable ventilation.

Theoretical background:

The iodide-catalyzed decomposition of hydrogen peroxide produces oxygen gas:

The experimental rate law is first order in both peroxide and iodide.

Hydrogen peroxide reacts vigorously with potassium iodide. Energy is liberated and the reaction takes place so rapidly that the temperature of the reaction solution rises. Hence the decompostion of hydrogenperoxide can be monitored by following the change in the temperature of the reaction mixture with time.

Experimental procedure:

Fig. 1: Experiment set-up

The temperature sensor is connected to the input Sensor2 of the CHEMBOX.

The Dewar vessel is fitted with a magnetic stirring bar. 75 mL of 10 % hydrogen peroxide solution are pipetted into the Dewar vessel and 8 mL of the 0.215 molar potassium iodide solution are added. The magnetic stirrer is started. On the Dewar vessel is placed a plastic cover, whose hole is fitted with a temperature sensor. Now the sensing software is started.

The real-time graph of the temperature rise is displayed on the screen (Fig. 2). The temperature is recorded until the maximum temperature achieved begins to fall. The reaction is then complete.

In addition the experiment is carried out using a 0.1075, 0.3225 and a 0.43 molar solution of potassium iodide.

Fig. 2: Realtime graph 0.215 molar potassium iodide solution

Data analysis using Excel :

A plot of T [ °C ] against t [ s ] is created. A best fit straight line is drawn through the highlighted data points of the linear portion of the individual temperature curves. The coefficient before x in the straight line equations (y = ax + b) specifies the value for the slope m (Fig. 3), which also can be determined directly on the measuring screen of Chemex (Fig. 2).

Fig. 3: Effect of concebntration on rate
1: 0.215 M 2: 0.3225 M 3: 0.43 M potassium iodide solution

Results:

slope

Fig. 4: Plot of the slope m versus the molarity of the iodide solution

The reaction rate is proportinal to the concentration of the catalyst (Fig. 4) - see experiment Decomposition of Hydrogen Peroxide catalyzed by Potassium Dichromate. The temperature curves show the reaction process typical for catalytic reactions. After an induction phase the reaction proceeds (Fig. 2 and 3).

References:
Computer-Interfaced Experiments Kinetics: Catalyzed Decomposition of Hydrogen Peroxide - First Order Reaction
Computer-Interfaced Experiments Kinetics: Decomposition of Hydrogen Peroxide catalyzed by Dichromate
Computer-Interfaced Experiments Enzyme Kinetics: Enzymatic Decomposition of Hydrogen Peroxide
Demonstration Experiment on Video Decomposition of Hydrogen Peroxide with Catalase
Kyle Smith und Mark Iannone Improved Data Analysis for an Adiabatic Kinetics Experiment

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