Investigate how varying the concentration of Sodium thiosulphate solution affects the rate of reaction with Hydrochloric Acid.

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Affect of Concentration

I am going to investigate how varying the concentration of Sodium thiosulphate solution affects the rate of reaction with Hydrochloric Acid.

The equation for the reaction is:

Sodium thiosulphate + Hydrochloric Acid           Sodium Chloride +   Water  +  Sulphur + Sulphur dioxide

Na2S2O3(aq)     +        2HCl(aq)                          2NaCl(aq)    +    H2O(l)  +      S(s)   +      SO2(aq)

This reaction has a definite end (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.

I predict that the greater the concentration of Sodium thiosulphate solution in the experiment, 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 certain temperature point.  After this, the solution will not react within a reasonable time because the solution will begin to decompose.

        I think that the concentration of a solution affects 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 substance. Because there are more molecules about, the frequency of successful collisions is greater, and the reactions happen faster.

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Prediction

I predict that when I add more water to the sodium thiosulphate solution, the time it takes for the cross to disappear will lengthen.  I predict this because, for particles to react they must collide with each other. If there is a higher concentration of sodium thiosulphate particles in a given volume there, is a higher chance of the particles colliding together and reacting. This is because they are so close together. If you weaken the solution, (so there is a much lower concentration of sodium thiosulphate particles to react with the hydrochloric acid,) then there is ...

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