How many electrons are transferred in the balanced equation?

Question

Al³⁺(aq) + Hg(s) → Al(s) + Hg²⁺(aq)

Answer 1

Oxidation eqn: Al³⁺ + 3e^- → Al(s)

Reduction eqn: Hg(s) → Hg²⁺(aq) + 2e^-

However, you need to balance to equations to have an equal number of electrons. The least common multiple of 3 and 2 is 6, so you'll need to multiply the equations accordingly.

Oxidation eqn: (Al³⁺ + 3e^- → Al(s)) * 2

Reduction eqn: (Hg(s) → Hg²⁺(aq) + 2e^- ) * 3

Oxidation eqn: 2Al³⁺ + 6e^- → 2Al(s)

Reduction eqn: 3Hg(s) → 3Hg²⁺(aq) + 6e^-

TLDR: 6 electrons are transferred in the global reaction.

Answer 2

Al³⁺ +3e--> Al

Hg --- Hg²⁺ + 2e

Find the lowest common multiple between 3 and 2: 6

So 6 electrons are transfered.

Answer 3

First, as always, balance the equation: 2 Al³⁺ + 3 Hg → 2 Al + 3 Hg²⁺

Then, find your half equations:

2 Al³⁺ + 2*3e → 2 Al

3 Hg → 3 Hg²⁺ + 3*2e

What’s transferred, then, is 2*3 electrons, which is 6.