Question

Ionic product of water increases, if:
A.Pressure is reduced
B.${{\text{H}}^ + }$ is added
C.${\text{O}}{{\text{H}}^ - }$ is added
D.Temperature increases

Answer 1

Hint:Ionic product of water is the dissociation of water molecules into its individual ions, hydrogen ion and hydroxyl ion. When the temperature is increased, the number of hydrogen ions and the number of hydroxyl ions increases.

Complete step by step answer:
Water in its pure form conducts electricity. Thus, water is a weak electrolyte. The dissociation of water occurs as follows:
${{\text{H}}_{\text{2}}}{\text{O}} \rightleftharpoons {{\text{H}}^ + } + {\text{O}}{{\text{H}}^ - }$
The equation for dissociation constant of water is as follows:
$K = \dfrac{{\left[ {{{\text{H}}^ + }} \right]\left[ {{\text{O}}{{\text{H}}^ - }} \right]}}{{\left[ {{{\text{H}}_2}{\text{O}}} \right]}}$
Where $K$ is the dissociation constant of water.
$K\left[ {{{\text{H}}_2}{\text{O}}} \right] = \left[ {{{\text{H}}^ + }} \right]\left[ {{\text{O}}{{\text{H}}^ - }} \right]$
${K_w} = \left[ {{{\text{H}}^ + }} \right]\left[ {{\text{O}}{{\text{H}}^ - }} \right]$ …… $K\left[ {{{\text{H}}_2}{\text{O}}} \right] = {K_w}$
Where ${K_w}$ is the ionic product of water.
Thus, the ionic product of water is the product of molar concentration of hydrogen ion and the molar concentration of hydroxyl ion.
The value of an ionic product of water at ${25^ \circ }{\text{C}}$ is $1 \times {10^{ - 14}}$.
The degree of dissociation of water increases with an increase in temperature. As the temperature increases, the molar concentration of hydrogen ions and hydroxyl ions increases. Thus, the ionic product of water increases with increase in temperature.
Thus, the ionic product of water increases, if temperature increases.

Thus, the correct option is option (D).

Note: While writing the expression for the ionic product of water, the molar concentration of water molecules is not included. Water undergoes self-ionization. Thus, water can act as acid as well as base.
When an acid is added to water the ionic product of water remains constant but the concentration of hydrogen ion increases. Thus, the concentration of hydrogen ions is higher than the concentration of the hydroxyl ions.