Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it. (a) What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper? (b) Write a balanced chemical equation for the reaction taking place.
S(s) + O₂(g) → SO₂(g) SO₂(g) + H₂O(l) → H₂SO₃(aq)
What will be the action of gas on dry litmus paper?
Sulphur dioxide gas has no action on dry litmus paper because without water, it cannot show its acidic nature.
What will be the action of gas on moist litmus paper?
Sulphur dioxide gas turns moist blue litmus paper red because it dissolves in water to form sulphurous acid (H₂SO₃), which is acidic.
Explanation
(a(i)) Acidic properties require the presence of water for ionisation. (a(ii)) SO₂ dissolves in water to form H₂SO₃, an acidic solution. (b) Sulphur burns in oxygen to form SO₂, which dissolves in water to form sulphurous acid.