Oxidation and Reduction

Question 1

What happens to electrons in an oxidation reaction?

Answer 1

Electrons are lost.

Question 2

What happens to electrons in a reduction reaction?

Answer 2

Electrons are gained.

Question 3

How is an oxidation reaction written as a half equation? How is this explained?

Answer 3

Starting with the atom, after the arrow, the ion is written with a positive charge and electrons are added at the end.

Mg = Mg2+ + 2e-

The electrons are no longer in the atom, so it has lost electrons - oxidation.

Or, starting with the ion, after the arrow, the atom is written and the electrons are added at the end.

2I- = I2 + 2e-

The electrons are not in the atom, so it has lost electrons - oxidation.

Question 4

How is a reduction reaction written as a half equation? How is this explained?

Answer 4

Starting with the ion, if it gains electrons, the electrons are added next, and the atom is written after the arrow.

2H+ + 2e- = H2

The ion is gaining electrons to form the neutral atom, therefore it is reduction.

You can also have an ion written after the arrow when not enough electrons have been gained to make it neutral:

Fe3+ + e- = Fe2+

Again, the ion is gaining electrons, therefore it is reduction.