Use of Catalyst – If a catalyst is present then the reaction rate will increase due to the fact it replaces the amount of energy needed for the collision, allowing for more collisions to take place.
Aim: We will be investigating the rates of reaction when we will mix together sodium thiosulphate and hydrochloric acid.
The concentration of sodium thiosulphate was changed by adding water.
The solution was tested to see if it goes cloudy by observing an ‘X’.
I will carry out trial runs to decide which of the four factors that affect rates of reaction I will measure in my final run. The experiments I could do are: • • • Measuring volume of gas produced Measuring precipitation (because sulphur is produced) e.g.
look for ‘X’ to disappear Measure mass lost The reaction of the experiment happens with this formula: Na2 S2 O3 HCl = 2Na Cl H2O SO2 S The importance of running trial runs is to see whether any mistakes are made and to prevent them from happening in the final run. Trial run 1 had a wider range however trial run 2 hadn’t.
Different people watching when the ‘X’ disappeared meant that there are more likely to be errors and could make our results less reliable.
Our results show a clear patter – as the concentration of sodium thiosulphate increased, the time taken for the ‘X’ to disappear decreased; this proves the collision theory.
Results of trial run 1: Concentration (%) Volume of sodium thiosulphate (ml) Volume of H2O (cm3) Volume of acid (ml) Time taken for ‘X’ to disappear (s) 20 5 20 2 319.46 60 15 10 2 34.86 100 25 0 2 18.5 3 Evaluation: One of the weaknesses of the trial run was that the person recording the time changed and this could of lead to slight deviation in the result.
However, other factors like the room temperature and the amount of acid in the solution were kept controlled to keep the test as fair as possible.