Sodium thiosulphate
Hydrochloric acid
Beaker
Stopwatch
Scrap paper
Pen
Method
A cross is marked on the piece of paper and a beaker containing 15cm² of sodium thiosulphate solution is put on the cross. The cross should be visible through the solution. 5cm³ of Hydrochloric acid is added to the solution, and the stopwatch started at the same time. The cross on the paper will become fainter as time progresses due to the precipitate, which forms.
The stopwatch should be stopped when the cross can no longer be seen through the solution. The experiment was repeated at different temperatures.
Fair Testing
The concentration of the solutions was kept the same at all time, in all experiments. The beaker was replaced by a new, clean beaker after each experiment to avoid residual traces of previous solutions affecting the results. The same cross should be used for the entire experiment, if a paler cross is used this could affect the results. The beakers should be the same size, the same condition, and have been kept in the same environment before the experiment. This will ensure that the testing is fair: if the beakers are cooler before the experiment it will affect the rate of reaction; if the beakers are different sizes then this will also affect heat dispersion and the rate of reaction, therefore affecting the results. The experiments should both take place out of direct sunlight, so that the heat won’t affect the results. A digital thermometer should be used as a conventional thermometer could be wrong, and also subject to human error. Convection currents would also have an effect upon the mixing of the solution, and I would have to ensure that there was no mixing of the solution as a result of movement of the thermometer.
Results
Explanation of Results
The first set of results I got where obviously wrong. The beakers may have been dirty, or I may have measured the concentration wrong. I decided to do the whole experiment again, and the second time I got better results. The second results support the prediction that the higher the temperature, the quicker the reaction. The friends results do not offer much help with a comparison to my results, but do however, obey the statement that the higher the temperature, the quicker the reaction will take place.
Conclusion
It is evident that I was correct to predict that the rate of reaction increases as the temperature of the reactants increases. The cooler the hydrochloric acid, the longer it will take before the marked cross cannot be seen anymore. Although heating the hydrochloric acid increases the speed of the reaction the temperature of the beaker and room also have an adverse affect on the rate of the reaction.
Evaluation
The experiment went wrong the first time, but the second experiment backs up the prediction, and shows it to be right. The results show the prediction to be true. As the temperature rises, so does the rate of reaction. I think it would have been better had the experiment been repeated a number of times at least 3, and the average temperature changes used as the results.
If I were to do this experiment again this is what I would do.
