Year 12s: what will be the first way you research your future options? >>

Can someone help with this A Level Chemistry Question?

How would I do this chemistry question? I’ve figured out I would need to use the equation Cu^2+ + S203^2- —-> CuS2O3. I will post a picture below because I can’t see how to attach it here :smile:

Reply 1

bee115

Original post by bee115

Reply 2

charco

Study Forum Helper

Original post by bee115

You are on the wrong track.

Copper(II) ions react with iodide ions from the potassium iodide to give copper(I) ions and iodine:

2Cu²⁺(aq) + 4I^-(aq) ==> 2CuI(s) + I₂(aq)

The thiosulfate ions then react with the iodine solution:

2S₂O₃^2-(aq) + I₂(aq) ==> S₄O₆^2-(aq) + 2I^-(aq)

This allows us to determine the concentration of copper(II) in a solution. The excess potassium iodide ensures that all of the copper(II) reacts.
The thiosulfate solution is added until the colour of the iodine is completely discharged (gone) - a starch indicator is usually added near the end point of the titration.