Question

Define the terms “oxidising agent” and “reducing agent”.

Answer 1

• The reaction in which one or more electrons are lost by a species is called an oxidation reaction. In the oxidation process, the oxidation number of a substance increases by the loss of electrons.
• The reaction in which one or more electrons are gained by a species is called a reduction reaction. In the reduction process, the oxidation number of a substance decreases by the gain of electrons.
• Oxidizing agent is the species that oxidize another substance but reduces itself in the reaction. While the reducing agent is the species that reduces other substances but oxidizes itself in the reaction. Example,

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\to {\mathrm{MgCl}}_2\left(\mathrm{s}\right)$

• Oxidation number of Magnesium (Mg) is 0 in Mg and +2 in Magnesium chloride (MgCl₂). Due to an increase in the oxidation number from 0 to +2, Mg undergoes oxidation in the reaction. On the other hand, the oxidation number of Chlorine (Cl) is 0 in Chlorine gas (Cl₂) and -1 in MgCl₂. Due to a decrease in the oxidation number from 0 to -1, Cl₂ undergoes a reduction in the reaction.
• Since Magnesium (Mg) undergoes oxidation in the reaction, it acts as the reducing agent. On the other hand, Chlorine gas (Cl₂) undergoes a reduction in the reaction, it acts as the oxidizing agent.