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.
ScienceClass 10CBSEAnswered 27 Mar 2026
Answer
Solution: a) When sulphur powder is burnt in the air sulphur-di-oxide is formed.
(i) Sulphur-di-oxide does not have any effect on dry litmus paper.
(ii) Sulphur-di-oxide turn the moist litmus paper from blue to red as contact of SO2 with water turns to sulfurous acid.
(b) S(s) + O2(g) → SO2(g)
SO2(g) + H2O →H2SO3
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