Chemistry HW help

Question

Complete and balance the following redox reaction in basic solution. Be sure to include the proper phases for all species within the reaction. NO3- (aq) + AsH3(s) -> NH3(g) + As(s)

Answer 1

NO3- (aq) + AsH3(s) -> NH3(g) + As(s)

NO3-(aq) ==> NH3(g) .. unbalanced reduction reaction

NO3-(aq) ==> NH3(g) + 3H2O(l) .. balanced for N and O

NO3-(aq) + 9H2O(l) ==> NH3(g) + 3H2O(l) + 9OH-(aq) .. balanced for N, O and H

NO3-(aq) + 9H2O(l) + 8e- ==> NH3(g) + 3H2O(l) + 9OH-(aq) .. balanced for N, O, H and charge

AsH3(s) ==> As(s) .. unbalanced oxidation reaction

AsH3(s) + 3OH-(aq) ==> As(s) + 3H2O(l) .. balanced for As, O, and H

AsH3(s) + 3OH-(aq) ==> As(s) + 3H2O(l) + 3e- .. balanced for As, O, H and charge

Multiply reduction rxn by 3 and oxidation rxn by 3 to equalized electrons. Add the two rxns together and combine / cancel like terms to get the final balanced redox equation:

3NO3-(aq) + 27H2O(l) + 24e- ==> 3NH3(g) + 9H2O(l) + 27OH-(aq)

8AsH3(s) + 24OH-(aq) ==> 8As(s) + 24H2O(l) + 24e-

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3NO3-(aq) + 27H2O(l) + 24e- + 8AsH3(s) + 24OH-(aq) ==> 3NH3(g) + 9H2O(l) + 27OH-(aq) + 8As(s) + 24H2O(l) + 24e-

3NO3-(aq) + 8AsH3(s) ==> 3NH3(g) + 6H2O(l) + 3OH-(aq) + 8As(s) .. balanced redox equation

Answer 2

The balanced redox reaction in basic solution is:

NO3^-(aq) + AsH3(s) + 6OH^-(aq) → NH3(g) + As(s) + 3H2O(l)

The oxidation half-reaction is:

AsH3(s) → As(s)

The reduction half-reaction is:

NO3^-(aq) + 3H2O(l) + 3e^- → NH3(g) + 3OH^-(aq)

To balance the electrons, we need to multiply the oxidation half-reaction by 3 and the reduction half-reaction by 2. This gives:

3AsH3(s) → 3As(s) + 6e^-

2NO3^-(aq) + 6H2O(l) + 6e^- → 2NH3(g) + 6OH^-(aq)

Adding these two half-reactions together gives:

2NO3^-(aq) + 3AsH3(s) + 6OH^-(aq) → 2NH3(g) + 3As(s) + 3H2O(l)

Finally, we can cancel out the common species on both sides of the equation to get the balanced redox reaction in basic solution:

NO3^-(aq) + AsH3(s) + 6OH^-(aq) → NH3(g) + As(s) + 3H2O(l)