A-Level Investigation - Rates of Reaction – The Iodine Clock

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MCB

A-Level Investigation

Rates of Reaction - The Iodine Clock

Aim: carry out investigations to determine the rate equation for the oxidation of iodide ions by hydrogen peroxide in acid solution. Investigate the effect of various transition metal catalysts on the reaction rate.

Introduction to research

The research of this project involved investigation of a range of scientific literature available from Oxford University's online science library, various chemistry texts and other Internet sources.

The Iodine clock reaction

This reaction has been used repeatedly down the years in the study of reaction rates. Most famously by Harcourt and Esson in the late 18th - early 19th century. The reaction between hydrogen peroxide and iodide ions is still known as the Harcourt-Esson reaction.

The Iodine Clock reaction can be represented by the half equations:

H2O2 (aq) + I- (aq) --> IO- (aq) + H2O (l) Slow [1]

IO- (aq) + H3O+ (aq) - HIO (aq) + H2O (l) Fast [2]

HIO (aq) + H3O+ (aq) + I- (aq) --> I2 (aq) + 2H2O (l) Fast [3]

Overall:

2H+ + H2O2 + 2I- --> 2H2O