Question

Salt formation from acids and alkalis can be stated essentially as the neutralization of hydrogen and hydroxide ions. Illustrate it with one example of neutralization reaction.

Answer 1

1. Neutralization reaction

Neutralization reactions occur between acids and bases forming salt and water. The acids contain protons and the bases contain hydroxide ions which get neutralized to form water. The ions remaining in the solution form a salt, which can be either soluble or insoluble in an aqueous solution.

2. Salt formation

Acids and bases dissociate in solution and remain in their ionic form. Consider the neutralization reaction of Hydrochloric acid $\left(\mathrm{HCl}\right)$ and Sodium hydroxide $\left(\mathrm{NaOH}\right)$. In solution, they remain in ionic form. And, when the solutions of Hydrochloric acid and Sodium hydroxide are mixed, the resulting solution will contain Sodium ions $\left({\mathrm{Na}}^{+}\right)$, Hydroxide ions $\left({\mathrm{OH}}^{-}\right)$, Hydrogen ions $\left({\mathrm{H}}^{+}\right)$ and Chloride ions $\left({\mathrm{Cl}}^{-}\right)$.

The ionic form of the reaction in solution is:

$$\begin{gathered} {\mathrm{Na}}^{+}{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\to {\mathrm{Na}}^{+}{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ (\mathrm{Sodium}(\mathrm{Hydrochloric}(\mathrm{Sodium}(\mathrm{Water}) \\ \mathrm{hydroxide})\mathrm{acid})\mathrm{chloride}) \end{gathered}$$

Sodium ions and Chloride ions form Sodium chloride salt, which remains in solution in its ionic form. On cancelling the Sodium ions and Chloride ions from both sides of the reaction, the reaction will become

$$\begin{gathered} {\mathrm{OH}}^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}^{+}\left(\mathrm{aq}\right)\to {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \left(\mathrm{Hydroxide} \\ \mathrm{ion}\right)\left(\mathrm{Proton}\right)\left(\mathrm{Water}\right) \end{gathered}$$

Therefore, the salt formation from acids and alkalis can be stated essentially as the neutralization of hydrogen and hydroxide ions.