Investigating the effect of concentration on the rate of reaction between Sodium thiosulphate and hydrochloric acid

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Investigating the effect of concentration on the rate of reaction between Sodium thiosulphate and hydrochloric acid

Plan

In this investigation I am going to find out how the concentration of an acid affects the rate of reaction between the two substances Sodium thiosulphate and hydrochloric acid. The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. I have chosen to investigate the effect concentration has on a reaction. To do this I will mark a cross below the conical flask the solution is in and time how long it takes to disappear from view. I have decided to keep the concentration of sodium thiosulphate the same (0.2M) and change the concentration of the hydrochloric acid varying between 0.2M and 1M, going up in 0.2’s. I will also take 3 results for every different concentration so that I can work out the average and therefore get a more accurate result to plot on my graph.

Preliminary work

I found that when sodium thiosulphate and hydrochloric acid are mixed the solution turns cloudy white, and then yellow. I found out that it would be best not to stir the solution because this would speed up the reaction and we would not be able to stir it the same each time, so to make it fairer we are not going to stir the solution. We found that the best time to start timing would be from when the last of the acid was poured into the conical flask.

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Sodium thiosulphate (aq) + hydrochloric acid (aq) = sodium chloride (aq)

                                                                                 + sulphur (s)

                                                                                 + sulphur dioxide (g)

  ...

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