Question

How is the concentration of hydroxide ions $\left({\mathrm{OH}}^{-}\right)$ affected when excess base is dissolved in a solution of Sodium hydroxide?

Answer 1

Base:-

• Substances that produce hydroxide ions$\left({\mathrm{OH}}^{-}\right)$when dissolved in water are called a base.
• More the concentration of the hydroxide ion is, the more the basicity of the substance is.
• Some examples are- Sodium hydroxide$\left(\mathrm{NaOH}\right)$, Calcium hydroxide$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$

Affect of addition of excess base:-

• In the solution of Sodium hydroxide$\left(\mathrm{NaOH}\right)$, if a base is added, it increases the concentration of hydroxide ions$\left({\mathrm{OH}}^{-}\right)$.
• Also the Sodium hydroxide itself dissociates to give out hydroxide ions.

$\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Sodium}\mathrm{ions}}{{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydroxide}\mathrm{ions}}{{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)}$

• Hence the concentration of hydroxide ions in the solution increases per unit volume.

Therefore, the concentration of hydroxide ions $\left({\mathrm{OH}}^{-}\right)$ increases per unit volume, when excess base is dissolved in a solution of Sodium hydroxide$\left(\mathrm{NaOH}\right)$