A grade GCSE chemistry coursework - Rates of Reaction Decomposition of Sodium Thiosulphate
This is an investigation about the decomposition of sodium thiosulphate. There are many factors (variables) which determine how fast or slow the reaction can take place (rate of reaction). These are: * Initial volume of sodium thiosulphate. * The initial volume of hydrochloric acid. * The initial volume of water. * The temperature of the reaction mixture. * The concentration of the sodium thiosulphate. * The concentration of hydrochloric acid. * Changing the pressure
In this particular investigation I am going to find out how heat affects the rate of reaction in the reaction of sodium thiosulphate with hydrochloric acid. Sulphur forms a colloidal precipitate which gives the solution a cloudy yellow appearance. The rate of reaction can be found by measuring the time for the solution to become cloudy. I will measure the amount of time for the solution to become completely cloudy by drawing a cross on a piece of paper and place it under the beaker. As the reaction takes place, the solution becomes cloudy and the cross gradually disappears. The equation for this reaction is:
Sodium Thiosulphate + hydrochloric acid → sodium chloride + water + sulphur dioxide + sulphur
Na2S2O3(aq) + 2NaCl(aq) 2NaCl(aq) + H2O(l) + S(s) + SO2(g)
Preliminary work
I have done preliminary work to work out the right amounts/concentrations etc to use and also to decide the best range results.
Below is a table to show my results:

From the table above I can see that, as the temperature increases, the time taken for the cross to disappear decreases. This means that the rate of reaction increases because of the fact that there are more collision and so more successful collisions. Also, for every increase of
10°C, the time taken for the cross to disappear is roughly