Define (i) oxidation, (ii) reduction, in terms of electron transfer - Leaving Cert Chemistry - Question c - 2011

Reduction is defined as the gain of electrons in a chemical reaction. It is a process where an atom or ion decreases its oxidation state.

In this reaction, magnesium (Mg) is oxidised, while chlorine (Cl₂) is reduced. This is because magnesium loses electrons to form Mg²⁺ ions, resulting in an increase in its oxidation state. Conversely, chlorine gains electrons to form Cl⁻ ions, resulting in a decrease in its oxidation state.

To test for the chloride ion, add silver nitrate solution to the aqueous sample. A white precipitate of silver chloride (AgCl) will form, indicating the presence of chloride ions. This precipitate is soluble in ammonia, which can be used for further confirmation.