Investigation- To investigate the factors involved in the following
Na2S2O3(aq) + 2HCl(aq) à 2NaCl(aq) + H2O(l) + SO2(aq) + S(s)
The following are variables which will affect my investigation.
Temperature, Pressure, Concentration of Na2S2O3, Concentration of HCl,
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
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...