Question

Write three properties of acids.

Answer 1

Acid:

Acids are substances that furnish one or more Hydrogen ions as the only positive ion.

Examples: Hydrochloric acid $\left(\mathrm{HCl}\right),$ Sulfuric acid $\left({\mathrm{H}}_2{\mathrm{SO}}_4\right)$, Ethanoic acid $\left({\mathrm{CH}}_3\mathrm{COOH}\right)$, etc.

The dissociation of Hydrochloric acid can be represented as: $\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{\mathrm{Hydrogen}\mathrm{ion}}{{\mathrm{H}}^{+}\left(\mathrm{aq}\right)}+\underset{Chlorideion}{{\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)}$

Physical properties of an acid:

• They are sour in taste.
• They are corrosive in nature. Some of them cause painful burns on the skin.
• Some of them are solids and some of them are liquid at room temperature. For example, Boric acid, Oxalic acid, Tartaric acid etc. are solid at room temperature whereas Carbonic acid, Nitric acid, and Acetic acids are liquid at room temperature.

Chemical properties of acid:

• They react with metals (above Hydrogen in the metal reactivity series) to give Hydrogen gas.

$$\begin{gathered} \underset{(\mathrm{Sodium}\mathrm{metal})}{2\underbrace{\mathrm{Na}\left(\mathrm{s}\right)}}+\underset{(\mathrm{Hydrochloric}\mathrm{acid})}{\underbrace{2\mathrm{HCl}\left(\mathrm{s}\right)}}\to \underset{(\mathrm{Sodium}\mathrm{chloride})}{\underbrace{2\mathrm{NaCl}\left(\mathrm{aq}\right)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{\underbrace{{\mathrm{H}}_2\left(\mathrm{g}\right)\uparrow }} \\ \underset{\left(\mathrm{Magnesium}\right)}{\underbrace{\mathrm{Mg}\left(\mathrm{s}\right)}}+\underset{(\mathrm{Sulphuric}\mathrm{acid})}{\underbrace{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}}\to \underset{(\mathrm{Magnesium}\mathrm{sulphate})}{\underbrace{{\mathrm{MgSO}}_4\left(\mathrm{aq}\right)}}+\underset{(\mathrm{Hydrogen}\mathrm{gas})}{\underbrace{{\mathrm{H}}_2\left(\mathrm{g}\right)\uparrow }} \end{gathered}$$

• When acids react with the bases they form salt and water. This reaction is known as the Neutralization reaction.

$\underset{(\mathrm{Sodium}\mathrm{hydroxide})}{\underbrace{\mathrm{NaOH}\left(\mathrm{aq}\right)}}+\underset{(\mathrm{Hydrochloric}\mathrm{acid})}{\underbrace{\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{(\mathrm{Sodium}\mathrm{chloride})}{\underbrace{\mathrm{NaCl}\left(\mathrm{aq}\right)}}+\underset{\left(\mathrm{water}\right)}{\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}$.

• Acids on reaction with metal Carbonate or metal Hydrogen carbonate give salt, water and Carbon dioxide.

$$\begin{gathered} \underset{(\mathrm{Calcium}\mathrm{carbonate})}{\underbrace{{\mathrm{CaCO}}_3\left(\mathrm{aq}\right)}}+\underset{(\mathrm{Hydrochloric}\mathrm{acid})}{\underbrace{2\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{(\mathrm{Calcium}\mathrm{chloride})}{\underbrace{{\mathrm{CaCl}}_2\left(\mathrm{aq}\right)}}+\underset{\left(\mathrm{Water}\right)}{\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{\underbrace{{\mathrm{CO}}_2\left(\mathrm{g}\right)}} \\ \underset{(\mathrm{Calcium}\mathrm{hydrogen}\mathrm{carbonate})}{\underbrace{\mathrm{Ca}{\left({\mathrm{HCO}}_3\right)}_2\left(\mathrm{aq}\right)}}+\underset{(\mathrm{Hydrochloric}\mathrm{acid})}{\underbrace{2\mathrm{HCl}\left(\mathrm{aq}\right)}}\to \underset{(\mathrm{Calcium}\mathrm{chloride})}{\underbrace{{\mathrm{CaCl}}_2\left(\mathrm{aq}\right)}}+\underset{\left(\mathrm{Water}\right)}{2\underbrace{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{\underbrace{2{\mathrm{CO}}_2\left(\mathrm{g}\right)}} \end{gathered}$$.