[NYM]

This is a bit embarrassing, but I just can't seem to solve this one.

It's actually quite simple:
3 Cu + 2 NO₃^- + 8 H⁺ -> 3 Cu²⁺ + 2 NO + 4 H₂O
4 I^- + 2 Cu²⁺ -> 2 CuI + I₂
I₂ + 2 S₂O₃^2-  + 2 Na⁺ -> 2 I^- + S₄O₆^2-

n(Na2S2O3) = 1 mole, find n(Cu).

I tried to simplify it:
3 Cu -> 2 Cu²⁺ -> I2 -> S₂O₃^2- -> Na₂S₂O₃
3/8n____1/4n____½n____½n_______n

Is this ok?

[Alberto_Kravina]

Just start from:

n_eq(S₂O₃^2-) = n_eq(Cu²⁺)

=>n(¹/₂ S₂O₃^2- = n(¹/₁ Cu²⁺)

I tried to simplify it:
3 Cu -> 2 Cu2+ -> I2 -> S2O32- -> Na2S2O3

The first step is wrong, as all copper atoms are oxidized to Cu²⁺, so it would be 3 Cu ? 3 Cu²⁺.
The last step is also wrong because elementar iodine (I₂) reacts with thiosulfate to tetrathionate and iodide anions.

[NYM]

Mmm... I'm afraid I don't understand. Could you elaborate a bit?
Thanks!

[DevaDevil]

Why dont you substitute the latter reactions in the first one:

3 Cu + 2 NO₃^- + 8 H⁺ -> 3 Cu₂+ + 2 NO + 4 H₂O
4 I^- + 2 Cu²⁺ -> 2 CuI + I₂
I₂ + 2 S₂O₃^2-  + 2 Na⁺ -> 2 I^- + S₄O₆^2-

-->

3 Cu + 2 NO₃^- + 8 H⁺ -> 3 Cu²⁺ + 2 NO + 4 H₂O
4 I^- + 2 Cu²⁺ + 2 S₂O₃^2-  + 2 Na⁺   -> 2 CuI + 2 I^- + S₄O₆^2-

-->

3 Cu + 2 NO₃^- + 8 H⁺ + 4*(3/2) I^- + 2*(3/2) S₂O₃^2-  + 2*(3/2) Na⁺  -> 2 NO + 4 H₂O + 2*(3/2) CuI + 2*(3/2) I^- + (3/2) S₄O₆^2-
=
3 Cu + 2 NO₃^- + 8 H⁺ + 6 I^- + 3 S₂O₃^2-  + 3 Na⁺  -> 2 NO + 4 H₂O + 3 CuI + 3 I^- + (3/2) S₄O₆^2-

Now the ratio Cu/Na₂S₂O₃ is easy to see

[Borek]

3 Cu + 2 NO₃^- + 8 H⁺ + 6 I^- + 3 S₂O₃^2-  + 3 Na⁺  -> 2 NO + 4 H₂O + 3 CuI + 3 I^- + (3/2) S₄O₆^2-

I^-?

[DevaDevil]

Sorry bout that lol; didn't take the time to fully look at reactants and products etc. :p
Does not matter for the ratio Cu/Na₂S₂O₃ though

And there is a mistake in the last reaction as well

I2 + 2 S2O32-  + 2 Na+ -> 2 I- + S4O62-
has to be:
I2 + 2 S2O32-  -> 2 I- + S4O62-

ofc the final reaction then has to be:

3 Cu + 2 NO₃^- + 8 H⁺ + 3 I^- + 3 S₂O₃^2-  --> 2 NO + 4 H₂O + 3 CuI +  (3/2) S₄O₆^2-

[NYM]

thanks :p