Iodine Clock Reaction
"CHEMISTRY REVIEW" PROJECT PAGES
This Project Page first appeared in the November 1996 issue of Chemistry Review, Volume 6, Number 2, Pages 14 and 15. Chemistry Review is published four times during the academic year by Philip Allan Updates and is a journal for post-16 students. It contains a variety of interesting and colourful articles aimed at 16-19 year-olds taking mainly AS and A2 courses in chemistry.
NOTE: Project Page is designed to help you think about your investigation. It is not intended to be a set of instructions for practical work and does not include a list of safety precautions. CHEMISTRY REVIEW accepts no responsibility if Project Page is used in any way as a set of instructions.
Clock reactions
If you choose a project that explores the kinetics of a chemical reaction you will need a way of measuring the rate of the reaction. Clock reactions provide an interesting way of doing this for some systems.
In a typical reaction the first part of a graph showing the concentration of product against time is approximately a straight line (see Figure 1). If you choose any value of concentration that lies on this straight line (say c1) the initial rate of reaction can be found by dividing this concentration by the time taken to reach it (t1).
[pic]
Figure 1
If you measure the time taken for the same concentration to be reached in a series of reactions, you will be finding the time for the same amount of product to be formed for each reaction. The shorter the time, the faster the reaction is occurring. You can therefore take 1/t as a relative measure of the initial rate of reaction.
The trick, of course, is knowing when the fixed amount of product has been formed. The following examples illustrate how this can be done.
Appearing blue
There are a number of so called 'iodine clock' reactions in which molecular iodine is one of the products. Probably the most famous of these is the reaction involving hydrogen peroxide and iodide
This Project Page first appeared in the November 1996 issue of Chemistry Review, Volume 6, Number 2, Pages 14 and 15. Chemistry Review is published four times during the academic year by Philip Allan Updates and is a journal for post-16 students. It contains a variety of interesting and colourful articles aimed at 16-19 year-olds taking mainly AS and A2 courses in chemistry.
NOTE: Project Page is designed to help you think about your investigation. It is not intended to be a set of instructions for practical work and does not include a list of safety precautions. CHEMISTRY REVIEW accepts no responsibility if Project Page is used in any way as a set of instructions.
Clock reactions
If you choose a project that explores the kinetics of a chemical reaction you will need a way of measuring the rate of the reaction. Clock reactions provide an interesting way of doing this for some systems.
In a typical reaction the first part of a graph showing the concentration of product against time is approximately a straight line (see Figure 1). If you choose any value of concentration that lies on this straight line (say c1) the initial rate of reaction can be found by dividing this concentration by the time taken to reach it (t1).
[pic]
Figure 1
If you measure the time taken for the same concentration to be reached in a series of reactions, you will be finding the time for the same amount of product to be formed for each reaction. The shorter the time, the faster the reaction is occurring. You can therefore take 1/t as a relative measure of the initial rate of reaction.
The trick, of course, is knowing when the fixed amount of product has been formed. The following examples illustrate how this can be done.
Appearing blue
There are a number of so called 'iodine clock' reactions in which molecular iodine is one of the products. Probably the most famous of these is the reaction involving hydrogen peroxide and iodide