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Investigation into the effect of concentration on the reaction between Sodium Thiosulphate and Hydrochloric Acid.

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Mike Taylor Science Coursework Investigation into the effect of concentration on the reaction between Sodium Thiosulphate and Hydrochloric Acid In this investigation I am going to investigate the effect of varying the concentration of Sodium Thiosulphate solution in a reaction with Hydrochloric Acid. I have chosen to do this reaction because it has a definite end point (when the cross disappears on the paper). The equation for the reaction is: Sodium Thiosulphate + Hydrochloric Acid � Sodium Chloride + Water + Sulphur + Sulphur dioxide Or the chemical equation: Na S O (aq) + 2HCL (aq) � 2 Na Cl (aq) + H O (l) + S (s) + SO (g) Equipment the equipment in which I will need for this experiment is: * 2 Measuring cylinders * Conical flask * Beaker * Stopwatch * Paper with cross marked on it * Sodium Thiosulphate solution * Hydrochloric Acid * Water * Goggles Prediction I predict that the greater the concentration of Sodium Thiosulphate solution the faster the chemical reaction will take place. ...read more.


I will conduct all the tests at room temperature because temperature has an effect on the rate of the reaction. The measures of Hydrochloric acid will all be the same (10cm). The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock. Method * I will pour 30mls of Sodium Thiosulphate or Na S O into 10cm of Hydrochloric Acid or HCL in a conical flask. * The concentration of the sodium Thiosulphate is 40mls and the concentration of the Hydrochloric Acid is 2 molars. * The flask will then be placed on a piece of paper with a black cross drawn on it. * Start the stopwatch when the sodium thiosulphate and hydrochloric acid are combined. * Stop the stopwatch when the solution is cloudy enough to prevent me seeing the cross. ...read more.


Evaluation The experiment roughly went according to plan but there were problems. For example, I only obtained two sets of results and then worked out an average. I could have done three tests to gain a more reliable average. There was also a human error involved when I was measuring liquids and looking for an end point in the reaction. Although the reaction I chose had a fairly definite end point it was still hard to tell whether the whole cross had disappeared or not. Instead of using a cross a light beam could be used and when the beam goes out that is the end point. A better standard of measuring cylinders and pipettes could be used. However, there was one result that was not really an anomaly as it still followed the pattern but was slightly different to the other result of the other test. When the amount of Sodium Thiosulphate was 10 cm, the time of the first test was 3043 compared to 287 in the second test. This could be human error, which is the reason for doing more tests. ...read more.

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