Question

Balance the following redox reaction

| 1. Al(s) + 2 H(aq) + 2 Cr → A13+ (aq) + H2 (g) + 2 CF (aq)

Answer 1

In given redox reaction, Cl^- is a spectator ion as it is present as same form in both reactants and products.

Net ionic reaction is :

Al(s) + H⁺ (aq) ----> Al³⁺ (aq) + H₂ (g)

Oxidation half reaction:

Al (s)----->Al³⁺ (aq) + 3e^-

Reduction half reaction:

2H⁺ (aq) + 2e^- -----> H₂ (g)

Both the reactions are balanced in terms of charge as well as atoms.

But total electrons lost must be equal to electron gained.

So, multiply balanced oxidation half by 2 and reduction half by 3 to equate electrons lost and gained.

Oxidation half becomes : 2Al (s) ----> 2Al³⁺(aq) + 6e^-

Reduction half becomes : 6H⁺ (aq) + 6e^- ----> 3H₂ (g)

Adding the above two reactions and canceling the electrons, final reaction is

2Al (s) + 6H⁺ (aq) -----> 2Al³⁺ (aq) + 3H₂ (g)

Adding 6Cl^- (aq) on both sides as spectator ion:

2Al (s) + 6H⁺ (aq) + 6Cl^- (aq) -----> 2Al³⁺ (aq) +  6Cl^- (aq) + 3H₂ (g)