Amphoteric oxides
Definition
A compound of oxygen and a metal. This compound reacts with both acids and bases to form salt and water
Physical properties of amphoteric oxides Since amphoteric oxides are metal oxides, amphoteric oxides are bases. ⇒ amphoteric oxides (ZnO, Al2O3, PbO) and bases → similar physical properties. ⇒ they are ionic compounds with giant ionic lattice structures.
- Amphoteric oxides have high melting and boiling points, solid at R.T.P
- Insoluble in water
- Good conductor of electricity when molten
Chemical properties of amphoteric oxides → metallic oxides that react with both acids and bases to form salts and water. Amphoteric oxide + dilute acid → salt + water (act as basic oxide) Amphoteric oxide + alkali → salt + water (act as acidic oxide)
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Reaction 1: hydrochloric acid + zinc oxide → zinc chloride + water 2HCl(aq) + ZnO(s) → ZnCl2(aq) + H2O(l)
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Reaction 2: Sodium hydroxide + zinc oxide → sodium zincate + water 2NaOH(aq) + ZnO(s) → Na2ZnO2(aq) + H2O (l)
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Reaction 3: hydrochloric acid + aluminum oxide → aluminum chloride + water 6HCl(aq) + Al2O3(s) → 2AlCl3(aq) + 3H2O(l)
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Sodium hydroxide + aluminum oxide → sodium aluminate + water 2NaOH(aq) + Al2O3(s) → 2NaAlO2(aq) + H2O(l)
One more amphoteric oxide → Lead(II)oxide (PbO)
Reaction 1 and 3, zinc oxide and aluminum oxide behave as basic oxides Reaction 2 and 4, they behave as acidic oxides.