Sarah Louise Redmond U5S 07/05/2007
GCSE Chemistry Coursework Investigation
To investigate the rate of reaction between
Sodium Thiosulphate and Hydrochloric Acid
Aim
My aim is to create an experiment so that I can measure the difference in reaction rates when Sodium Thiosulphate and Hydrochloric Acid are heated. When Sodium Thiosulphate and Hydrochloric acid are mixed they react to form Sulphur. It is the Sulphur that makes the reaction cloudy and the experiment is to see how long it takes for this solution to become cloudy when heated at different temperatures.
Factors Involved and Fair Testing
This experiment will contain only one variable, the temperature.
The constants are:-
- The concentrations of the Sodium Thiosulphate and Hydrochloric Acid. Also the volumes need to be kept constant so to keep the investigation fair.
- The apparatus used in the experiment needs to be kept exactly the same for each different temperature. If we use any apparatus that will need to be used in the next experiment we need to make sure that we wash them thoroughly so to avoid unnecessary reactions.
I need to keep these constants unvarying to keep the experiment accurate. I should already know what measurements to use for my concentrations from preliminary experiments, for example, I know that I have to choose a concentration that changes fairly slowly at room temperature because according to the rate of reaction theory, an increase in temperature will increase the reaction rate, therefore, if I start with a quick reaction at room temperature then the reaction at a higher temperature will be too quick for us to record the results accurately.
To keep this experiment fair I must keep everything apart from the temperature the same. This not only keeps the experiment fair but minimises the risk of mistakes because we are doing everything the same. Our only restriction is that our volume for our solution cannot exceed 50cm³. Also it could be difficult to tell when to stop the clock as it won’t be easy to the same range of cloudiness as we are relying on our eyes. Therefore this is why we are going to use a piece of paper with a “☺” written on it and place it under the beaker so that we know to stop the clock when we can no longer see the “☺”.