Practical investigations

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I am studying the reaction of propanone and iodine, using sulphuric acid as a catalyst. I used sodium hydrogencarbonate to quench the reaction and then titrated the reaction mixture against sodium thiosulphate. My tutor says I need to find an equation for the reaction that occurs during my titration. Could you please help?

Igloo writes
 
In the process you are studying, iodine is being slowly used up in its acid-catalysed reaction with propanone. The titration with a standard solution of sodium thiosulphate is designed to ascertain how much iodine remains at this particular stage of the reaction.
 
The equation representing the reaction which occurs during the titration is:
2Na₂S₂O₃(aq) + I₂(aq) -> 2NaI(aq) + Na₂S₄O₆(aq)
 
or, in an ionic form:
2S₂O₃^2-(aq) + I₂(aq) -> 2I^-(aq) + S₄O₆^2-(aq)

Risk assessment
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updated: 22 January 2006