Question

5. (12 points) For the following oxidation reduction reaction: Zn(s)+NO3 (aq) > Zn2*(aq) + N2(g) + H20 a. What are the oxidation numbers of the reactants and products? Oxidation Number in products Element Oxidation Number in reactants Zn N b. Write the balanced oxidation half-reaction and the reduction half-reaction. (in acid medium) Balanced oxidation half-reaction: Balanced reduction half-reaction: Write the balanced full reaction c.

Answer 1

Element	Oxidation no. in reactant	Oxidation no. in products
Zn	0	+2
N	+ 5	0
O	-2	-2

oxidation half reaction : Zn (s) $\rightarrow$ Zn ²⁺ (aq)

reduction half reaction :NO ₃^- (aq) $\rightarrow$ N ₂ (g)

Balance the half equations for atoms other than O and H.

oxidation half reaction : Zn (s) $\rightarrow$ Zn ²⁺ (aq)

reduction half reaction : 2 NO ₃^- (aq) $\rightarrow$ N ₂ (g)

Balance half equations for O atoms by adding H₂O to the side of half equation with less number of O atoms.

oxidation half reaction : Zn (s) $\rightarrow$ Zn ²⁺ (aq)

reduction half reaction : 2 NO ₃^- (aq) $\rightarrow$ N ₂ (g) + 6 H₂O

Balance half equations for H atoms by adding H⁺ to the side of half equations with less number of H atoms.

oxidation half reaction : Zn (s) $\rightarrow$ Zn ²⁺ (aq)

reduction half reaction : 2 NO ₃^- (aq)+ 12 H⁺ $\rightarrow$ N ₂ (g) + 6 H₂O

Balance above equations for charge by adding electrons.

oxidation half reaction : Zn (s) $\rightarrow$ Zn ²⁺ (aq) + 2 e ^-

reduction half reaction :2 NO ₃^- (aq)+ 12 H⁺ + 10 e ^-$\rightarrow$ N ₂ (g) + 6 H₂O

To make number electrons equal in both half equations, multiply oxidation by 5.

oxidation half reaction : 5 Zn (s) $\rightarrow$ 5 Zn ²⁺ (aq) + 10 e ^-

reduction half reaction :2 NO ₃^- (aq)+ 12 H⁺ + 10 e ^-$\rightarrow$ N ₂ (g) + 6 H₂O

Add two half equations

5 Zn (s) $\rightarrow$ 5 Zn ²⁺ (aq) + 10 e ^-

2 NO ₃^- (aq)+ 12 H⁺ + 10 e ^-$\rightarrow$ N ₂ (g) + 6 H₂O

Overall equation : 5 Zn (s) + 2 NO ₃^- (aq)+ 12 H⁺$\rightarrow$ 5 Zn ²⁺ (aq) + N ₂ (g) + 6 H₂O

Balanced oxidation half equation : 5 Zn (s) $\rightarrow$ 5 Zn ²⁺ (aq) + 10 e ^-

Balanced reduction half equation : 2 NO ₃^- (aq)+ 12 H⁺ + 10 e ^-$\rightarrow$ N ₂ (g) + 6 H₂O