Sodium Thiosulphate's Effect on the Rate of Reaction with Hydrochloric Acid

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Sodium Thiosulphate's Effect on the Rate of Reaction with Hydrochloric Acid Aim:

I am going to investigate how varying the concentration of Sodium

Thiosulphate affects the rate of reaction with Hydrochloric Acid.

Prediction:

The equation for the reaction is:

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Sodium Thiosulphate + Hydrochloric Acid Sodium Chloride + Water +

Sulphur + Sulphur dioxide

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Or: Na2S2O3 + 2HCl S + 2NaCl + H2O + SO2

This reaction has a definite end point (when the cross on the test

tube 'disappears'). The faster the cross 'disappears' the faster the

reaction and by timing how long this takes we can establish the rate

of reaction.

There are various factors affecting the rate of reaction that we need

to take into consideration, these are:

b Temperature - I will conduct all the tests at room temperature

(hopefully on the same day) because temperature has an effect on the

rate of the reaction.

b Shaking or stirring - I will try to keep jogging of the solutions to

a minimum so as not to alter the rate of reaction.

b Catalysts speed up reactions.

I predict that the greater the concentration of Sodium Thiosulphate

(hypo) in the solution the faster the chemical reaction will take

place. Therefore, the cross will disappear more quickly due to the

cloudiness of the solution. But only up to a point after this the

solution will not react within a reasonable time (i.e. under 30 min).

On a graph I predict it would be a plateau.

I think that the concentration of a solution effects the rate of

reaction because the rate of reaction depends on how frequently the

molecules of the reacting substances collide. A more concentrated

substance has more molecules for a given volume than a more dilute

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