Hey guys, I'm a 2nd year chemistry student and I am writing up my lab report for an andrews' titration experiment. It goes something like this:
Make standard solution (called solution "S"): 25ml of 0.1M Sodium thiosulphate, 25ml of 0.05M I2 in aqueous NaI (approx. 0.15M in NaI), dilute up to 250ml.
This is the reaction:
2S2O32- + I2 (+NaI) ----> 2I- + S4O62-
Now the titration: Take 25ml of "S", add 25ml of H2O, 25ml of conc. HCl and 2ml of chloroform, and titrate against 25ml of 0.05M KIO3.
This is the reaction:
IO3- + 6H+ + 4e------>I+ + 3H2O
Also, since this reaction is happening in a vast excess of hydrochloric acid, this reaction also happens:
I+ + 2Cl------->ICl2-
OK, my question is, I have to work out the reaction ratio for S4O62-/IO3-. I have worked it out to be 1:7, but I can't work out the exact equation for this mechanism, namely because I am not sure how they react.
Any ideas?