Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below

(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.

Explanation

(a) When sulphur is heated in air, sulphur dioxide gas is formed.
(i) The gas has no effect on dry litmus paper.
(ii) The gas dissolves in water present in moist litmus paper to form sulphurous acid `(H_(2)SO_(3))` which turns the moist blue litmus to red.
(b) `underset("heated")(S_((s)))+underset("from air")(O_(2(g)))overset(Delta)toSO_(2(g))`
`SO_(2(g)) + H_(2)O_((l)) to underset("Sulphurous acid")(H_(2)SO_(3(aq)))`