This is an investigation into the rate of a reaction and the factors that contribute to how fast a reaction will take place. Through the recording and analysis of raw data, this investigation also allows us to apply generally accepted scientific rules and to test them against results gained from accurate experimental procedures.
The aim of this experiment is to investigate the rate at which iodine is formed when the concentration and temperature of the reactants are varied, and to attempt to find the order and activation energy.
'THE IODINE CLOCK ' - This is the experiment that will be used to investigate reaction rates, and it is a reaction between acidified hydrogen peroxide and potassium iodide:
2H+(aq) + 2I¯ (aq) + H[-1] 2O2 (l) ÕI2 (aq) + 2H2O2 (aq)
Iodide ions are firstly oxidised by the hydrogen peroxide, as shown in the above equation. The iodine that is then produced reacts immediately reacts with thiosulphate ions as follows:
I2 (aq) + 2Na2S2O3 (aq) Õ 2NaI (aq) + Na2S406 (aq)
As soon as all of the thiosulphate ions have reacted with the iodine, the excess iodine molecules react with the 2% starch solution that is present in the reaction. This can be seen as an instant change in colour, from a colourless solution, to a deep purple coloured solution. This change in colour denotes the completion of the reaction. Factors affecting the rate of reactions:
All chemical reactions occur at a definite rate under particular conditions. In order to increase the rate at which reactions occur, the frequency at which reacting molecules collide must be increased.
This may be achieved in a number of ways:
1. By increasing the concentrations of reacting species.
2. By increasing the temperature.
3. By increasing the pressure (only really significant in reactions involving gases).
4. By the use of a suitable
Bibliography: 'Chemistry Students Book ' - Nuffield Advanced Science 'Chemistry In Context ' - Graham Hill And John Holman 'Basic Inorganic Chemistry ' - Cotton, Wilkinson, Gaus 'Inorganic And Physical Chemistry ' - A. Holderness 'Advanced Chemistry ' - P.R.S. Murray 'Chemistry In Focus ' - John Andrew And Paul Rispoli 'Chemistry ' - Ken Gadd And Steve Gurr