3305 words - 13 pages

Chemistry Investigation

Investigation- To investigate the factors involved in the following

reaction:

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

PLANNING STAGE

Variables:

The following are variables which will affect my investigation.

Temperature, Pressure, Concentration of Na2S2O3, Concentration of HCl,

Stirring.

The key variables which I'm going to investigate are Concentration of

Na2S2O3 and Concentration of HCl.

What I'm going to find out:

I'm going to find out what effect varying the above stated variables

has on the rate at which the reaction between Na2S2O3 and HCl takes

place.

What I expect to happen:

I predict that when I double the concentration of the Na2S2O3, the

rate of reaction will double. The relationship will be directly

proportional and the graph that I will get will be a straight line

thought the origin. The origin will be a point on the graph since if

there is no Na2S2O3 then there will be no reaction. The relationship

will only be directly proportional up to a certain point, when the

rate will level off and increasing the concentration further will have

no added effect.

I predict that when I double the concentration of the HCl, the rate of

reaction will double. Again the relationship will be directly

proportional, and the graph a straight line through the origin. If

there was no HCl then there would be no reaction and so the origin is

a point on the graph. Again the graph will level off when a further

increase in the concentration has no more effect.

Why I think this will happen:

For the reaction to take place the thiosulphate ion must be broken

down. The ion will be broken down when it collides with another

molecule successfully i.e.: with enough energy to overcome the energy

barrier or the activation energy. Once a successful collision has

taken place the reaction can happen.

When I double the concentration of X (either the Na2S2O3 or the HCl,

which ever is being varied.)then I am doubling the number of X

molecules in a given volume. If you keep the number of Y molecules

(either the Na2S2O3 or the HCl depending on what X is) constant then

what was originally a ratio of X:Y now becomes 2X:Y. Therefore the

chance of the Y molecules colliding with the X molecules has doubled.

I will assume that the number of successful collisions doubles

proportionally. This will mean that the rate will double. Since the

movement of the molecules is random and all the collisions happen by

chance, then you can't say the rate will double exactly. Therefore the

points will lie almost on a straight line through the origin (not

taking into account experimental error). When you reach a certain

point the number of X molecules will be in such an excess that

doubling the number further will have such a small...

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