Science
Almost all metals combine with oxygen to form metal oxides. Metal oxides are generally basic in nature. But some metal oxides show both basic as well as acidic behaviour. Different metals show different reactivities towards oxygen. Some react vigorously while some do not react at all.
(a) What happens when copper is heated in air ? (Give the equation of the reaction involved).
(b) Why are some metal oxides categorized as amphoteric ? Give one example.
(c) Complete the following equations :
(i) Na2O(s) + H2O(l) ⟶
(ii) Al2O3 + 2NaOH ⟶
OR
(c) On burning Sulphur in oxygen a colourless gas is produced.
(i) Write chemical equation for the reaction.
(ii) Name the gas formed.
(iii) State the nature of the gas.
(iv) What will be the action of this on a dry litmus paper ?
Acids Bases Salts
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Answer
(a) When copper is heated in air, it reacts with the oxygen present in air to form black copper oxide.
2Cu(s) + O2(g) 2CuO(s)
(b) Amphoteric metal oxides behave both as acidic as well as basic oxides.
Example : Aluminium oxide [Al2O3]
It reacts with hydrochloric acid to form water and aluminium chloride
Al2O3 + 6HCl ⟶ 2AlCl3 + 3H2O
It reacts with sodium hydroxide solution and produces water and sodium aluminate (NaAlO2).
Al2O3 + 2NaOH ⟶ 2NaAlO2 + H2O
(c)
(i) Na2O(s) + H2O(l) ⟶ 2NaOH
(ii) Al2O3 + 2NaOH ⟶ 2NaAlO2 + H2O
OR
(i) S + O2 ⟶ SO2
(ii) Sulphur dioxide gas is produced.
(iii) Sulphur dioxide is a non-metal oxide and acidic in nature.
(iv) As the litmus paper is dry there will be no change in colour of litmus.
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