Kinetic Analysis of the Iodine Clock Reaction: An Introduction

The “iodine clock” reaction involves the mixing of two colorless solutions to produce a solution which remains colorless for a precise amount of time, then suddenly changes to a deep purple-blue color (as seen in the demonstration below). The rate of the reaction, and hence the time it takes to change color, is controlled by the temperature and/or the concentrations of the reactants.

The iodine clock reaction involves the oxidation of iodide ion (I-) to dissolved tri-iodide ion (I3-):

6 H+ + IO3- + 8 I- $\to$ 3 I3- + 3 H2O

Triiodide ion (I3-) combines with starch indicator to produce the characteristic purple-blue color. Timing how long it takes for the blue color to appear allows the rate of the reaction to be measured.

The general rate law expression for this reaction is: rate = k[IO3-]x[I-]y[H+]z

In this assignment you will use experimental data to determine the rate law for the iodine clock reaction by using the method of initial rates. You will determine the reaction order for each reactant (IO3-, I- and H+) and the rate constant (k) for the reaction and state the rate law appropriately based on the values you obtain. You will also answer other questions based on your understanding of chemical kinetics as they apply to this reaction.

The assignment instructions are included on the next page.

Assignment Instructions

First download the Assignment: Kinetic Analysis of the Iodine Clock ReactionActions . This file contains the experimental data and questions that you need to answer to complete the assignment.

Also download a supplementary file Background: Kinetic Analysis of the Iodine Clock ReactionActions . This file contains background information about how the iodine clock reaction works, the experimental set up for how this reaction is analyzed, how the rate of the reaction is measured, and guidelines for how to apply the method of initial rates to determine the rate law.

Preparing and submitting your work

Answer the questions in the assignment. Restate at least part of each question before writing your answer so that it is clear which question you are answering. You can write your answers by hand or type them (or a combination of these).

Depending on how you wrote your answers, create a PDF, or take a picture or scan of each page or your work and convert to a PDF file . Make sure the quality is good enough to view clearly. If I cannot read it, I will not grade it.