Consider the following equation in aqueous solution: PO₃³⁻(aq) + SO₂(g) → PO₄³⁻(aq) + S²⁻(aq) Write the balanced half-reaction for the oxidation in acidic solution.

Answer 1

Hi Halle C. By now, you should be getting the hang of how to balance these redox reactions. I think I've done 3 or 4 of them on this web site, either submitted by you or others. Have you even tried to do this problem? We really don't like doing homework for people here on Wyzant. I will do this one, but I urge you to try them before posting, and tell us what you've done and where you are having a problem.

Half reactions:

PO₃^3- ==> PO₄^3-

PO₃^3- + H2O ==> PO₄^3- .. balanced for P and O

PO₃^3- + H2O ==> PO₄^3- + 2H⁺ .. balanced for P, O and H (using acid, H⁺)

PO₃^3- + H2O ==> PO₄^3- + 2H⁺ + 2e- .. balanced for P, O, H and charge = balanced oxidation reaction

SO₂ ==> S^2-

SO₂ ==> S^2- + 2H2O .. balanced for S and O

SO₂ + 4H⁺==> S^2- + 2H2O .. balanced for S, O, and H (using acid, H⁺)

SO₂ + 4H⁺ + 6e- ==> S^2- + 2H2O .. balanced for S, O, H and charge = balanced reduction reaction

Multiply oxidation reaction by 3 to balanced transfer of electrons. Then add the 2 equations.

3PO₃^3- + 3H2O ==> 3PO₄^3- + 6H⁺ + 6e-

SO₂ + 4H⁺ + 6e- ==> S^2- + 2H2O

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3PO₃^3- + 3H2O + SO₂ + 4H⁺ + 6e- ==> 3PO₄^3- + 6H⁺ + 6e- + S^2- + 2H2O

3PO₃^3- + H2O + SO₂ ==> 3PO₄^3- + 2H⁺ + S^2- .. balanced redox reaction