Simple Oxides


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Oxides of nonmetals have a tendency to be acidic, oxides of metals have a tendency to be basic, and oxides of elements in or close to the corner to corner band of semimetals are by and large amphoteric.

An oxide is a binary compound obtained when oxygen reacts with another element. On the premise of their oxygen content, oxides can be extensively arranged into mixed oxides and simple oxides.

Simple Oxides

Simple oxides are oxides that carry only that number of oxygen atoms as is allowed by the normal valency of its metal.

Example: H2O, MgO& Al2O3.

Mixed Oxides

Two simple oxides combine to form mixed oxides.

Example: Lead dioxide (PbO2) and lead monoxide (PbO) together form the mixed oxide Red lead (Pb3O4).

Ferric oxide (Fe2O3) and ferrous oxide (FeO) together form the mixed oxide Ferro-ferric oxide (Fe3O4).

Classification of Simple Oxides

Simple Oxides on the basis of their chemical behaviour can further be classified into acidic oxides, basic oxides, amphoteric oxides and neutral oxides.

Acidic Oxide

An oxide that reacts with water to give an acid is called as Acidic Oxide. Example: Oxides of non-metals, such as SO2, CO2, SO3, Cl2O7, P2O5, & N2O5, or oxides of metals with high oxidation states, such as CrO3, Mn2O7, &V2O5 are acidic in nature.

  • Sulphur dioxide dissolves and reacts in water to give sulphurous acid.

         SO2              + H2O      →     H2SO3
Sulphur dioxide          Water            Sulphurous acid

  • Chromic anhydride reacts with water give chromic acid.

         Cr2O3                + H2O         →      H2Cr2O4
Chromic anhydride          Water            Chromic acid

Basic Oxide

An oxide that reacts with water to give a base is called as a basic oxide.

Example: Oxides of most metals, such asNa2O, CaO, BaO, are basic in nature.

  • Calcium oxide reacts with water to give calcium hydroxide, a base.

      CaO             +      H2O        → Ca(OH)2
Calcium oxide           Water             Calcium hydroxide

Amphoteric Oxides

Some metallic oxides display dual behavior that is they show both the characteristics of acid as well as base. These metal oxides are known as Amphoteric Oxides. They can react with both alkalis as well as acids.

Example: Zinc oxide when reacts with concentrated sodium hydroxide behaves as an acidic oxide but when reacts with hydrochloric acid acts as a basic oxide.

     ZnO          +   2H2O    + 2NaOH           →  Na3Zn[OH]4     +       H2 
Zinc oxide          Water         NaOH(conc)          Sodium Zincate   Hydrogen

      ZnO       +      2HCl                    →         ZnCl2      +        H2O
Zinc oxide        Hydrochloric acid             Zinc chloride         Water

Aluminium oxide is another example that reacts with alkalis as well as acids.

Al2O3 (s) + 6NaOH (aq) + 3H2O (l) → 2Na3[Al(OH)6] (aq)

Al2O3 (s) + 6HCl (aq) + 9H2O (l)  → 2[Al(H2O)6]3+ (aq) + 6Cl- (aq)

Neutral Oxides

Neutral Oxides, as name suggests do not exhibit any tendency to form salts either with acids or bases.

Example: Nitrous oxide and Carbon monoxide are neutral oxides.

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Simple Oxides


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