Question

Oxides of metals are basic while those of non-metals are acidic. Explain.

Answer 1

Metal oxides:

1. Metal oxides are considered basic oxides because when the metal oxide reacts with a dilute acid it forms salt and water.
2. It is a neutralization reaction and occurs when an acid and base react with each other.
3. Also, when metal oxides are dissolved in water it forms a basic solution because these metal hydroxides release $\left({\mathrm{OH}}^{-}\right)$ ions.
4. It can be checked by dipping red litmus paper into the formed solution, the red litmus paper will turn blue, showing the solution is basic in nature.

Reaction of metal oxide with acid;

$\underset{(\mathrm{Copper}\mathrm{oxide})}{\mathrm{CuO}\left(\mathrm{s}\right)}+2\mathrm{HCl}\left(\mathrm{l}\right)\stackrel{}{\to }\underset{(\mathrm{Copper}\mathrm{chloride})}{{\mathrm{CuCl}}_2\left(\mathrm{s}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

Reaction of metal oxide with water;

$\underset{(\mathrm{Sodium}\mathrm{oxide})}{{\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{}{\to }\underset{(\mathrm{Sodium}\mathrm{hydroxide})}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}$

Non-metal oxides:

1. When non-metal oxides are dissolved in water it forms an acidic solution because these non-metal hydroxide release $\left({\mathrm{H}}^{+}\right)$ ions.
2. It can be checked by dipping blue litmus paper into the formed solution, the blue litmus paper will turn red, showing the solution is acidic in nature.

Reaction of metal oxide with base;

$\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+2\underset{(\mathrm{Sodium}\mathrm{hydroxide})}{\mathrm{NaOH}\left(\mathrm{aq}\right)}\stackrel{}{\to }\underset{(\mathrm{Sodium}\mathrm{carbonate})}{{\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Reaction of non-metal oxide with water;

$\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\stackrel{}{\to }\underset{(\mathrm{Carbonic}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)}$

Therefore, oxides of metals are basic while those of non-metals are acidic.