Question 9:

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.

Answer

(a) (i) There will be no action on dry litmus paper.

(ii) Since the gas is sulphur dioxide (SO₂), it turns moist blue litmus paper to red

because sulphur dioxide reacts with moisture to form sulphurous acid.

S_(s)   +   O_2(g)    →  SO_2(g)

                             Sulphur dioxide

SO_2(g) + H₂O_(l) → H₂SO_3(aq)

                          Sulphurous acid

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