For each of the following balanced oxidation–reduction reactions, (i) identify the oxidation numbers for all the elements in the reactants and products and (ii) state the total number of electrons transferred in each reaction. (b) 2 Hg²⁺(aq) + N₂H₄(aq) → 2 Hg(l) + N₂(g) + 4 H⁺(aq)

Key Concepts

Oxidation Numbers

Oxidation numbers are assigned to atoms in a compound to indicate their degree of oxidation or reduction. They help in identifying which atoms are oxidized and which are reduced during a chemical reaction. The rules for assigning oxidation numbers include that the oxidation number of an element in its elemental form is zero, and for monoatomic ions, it equals the charge of the ion.

Oxidation and Reduction

Oxidation refers to the loss of electrons by a substance, resulting in an increase in its oxidation state, while reduction is the gain of electrons, leading to a decrease in oxidation state. In a redox reaction, one species is oxidized and another is reduced, and the total number of electrons lost in oxidation must equal the total number gained in reduction.

Balancing Redox Reactions

Balancing redox reactions involves ensuring that the number of atoms and the total charge are the same on both sides of the equation. This often requires identifying half-reactions for oxidation and reduction, balancing them separately, and then combining them while accounting for the electrons transferred. The total number of electrons transferred indicates the extent of the redox process.