[ananasdoceu]

Hello all,

I am taking IB chemistry, and I have recently done a practical about the reaction between Na2S2O3, and FeCl3.
I used different catalysts such as CaSO4, CuSO4, FeSO4 and NiSO4.
I am sure that many of you are familiar with this experiment, however I am very new to chemistry, and I would like to know exactly what causes the colour change to occur between the first two compounds; why the solution becomes transparent after some time; and how do the other 4 compounds act as catalysts in the reaction?
I would also appreciate some chemical equations to show the reactions which occur.

Many thanks!!!!

[cliverlong]

I couldn't find this on Google so I looked in the unutterably tedious and poorly organised "Facts, Patterns and Principles" and found the following

Iron (III) is reduced to Iron(II) via the dark-violet unstable complex anion,[Fe(S₂O₃)₂]^-

2Fe³⁺(aq) + 2S₂O₃^2-  2Fe²⁺(aq) + S₄O₆^2-(aq)

Maybe the only item to pull out of that is thiosulphate (in common with its reaction with H⁺ and I₂), acts as a reducing agent - and itself becomes the tetrathionate ion.

I think it is a bit obscure for A-Level/IB to be honest.

I don't know if your question expects this.

Clive