Rates of Reaction

Investigating the rate of reaction between sodium thiosulphate and hydrochloric acid

I am going to measure the rate of the reaction when hydrochloric acid is added to sodium thiosulphate. I am going to investigate what effect the concentration of the sodium thiosulphate has on the reaction rate.

When sodium thiosulphate and hydrochloric acid are mixed, a yellow precipitate of sulphur is produced. The solution becomes increasingly difficult to see through as more and more sulphur is formed. This is how I plan to measure the rate of the reaction. I will place a laminated cross underneath the solution and will stop the stop clock when the cross can no longer be seen.

I aim to conduct a fair and safe investigation to determine what affects the rate of the reaction.

Variables.

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Possible independent variables are temperature, amount of hydrochloric acid, concentration of Hydrochloric acid, amount or concentration of sodium thiosulphate and whether or not a catalyst is added.

* My independent variable is going to be the concentration of sodium thiosulphate. * My dependant variable will be the rate of the reaction, or time taken for the reaction to take place. Watching the cross disappear as precipitation occurs and sulphur is formed as a solid will be the method used to realise the rate.

* My controlled variables will be the temperature, the concentration of hydrochloric acid, the amount of sodium thiosulphate and the amount of hydrochloric acid. I will try and control these as far as possible, and be as accurate as I can when measuring out the chemicals.

I will not be using a catalyst.

Prediction.

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I predict that the higher the concentration of sodium thiosulphate, the quicker it will react...

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...the result of this mix up, as maybe some residue remained in the burette, even after rinsing.

If there had been sufficient time, this result would have most certainly have been taken again.

The small red marks protruding from the points on my graph are attempted error bars. However, with the exception of the anomalous result, these were so absurdly small they are all but indiscernible.

Stability of conclusion.

Obviously, with more time, more readings would have been taken to form a more accurate curve on the graph. However, I believe that sufficient information was recorded to form a firm conclusion and to prove the aforementioned theory to be correct.

Bibliography:

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* www.purchon.com/chemistry.htm

* BBC bitesize revision (online).

* Website entitled: - Collisional Theory Of Reaction Rates

* The Learning Centre (online.)

* Chemistry Textbook.