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CTET Paper II (Mathematics and Science) Sep 2014 Solved Paper

Question Numbers: 61-63

Directions: Question are based on the following passage.

A teacher of Class VIII demonstrates the following activity in her class: “The teacher takes a small amount of sulphur in a spoon and burns it. She then puts the spoon into a tumbler with a lid to ensure that the gas produced does not escape. After a few minutes, she adds water to the tumbler.”

Question : 61 of 150

Marks: +1, -0

What happens if blue and red litmus paper are put into the tumbler?

Red litmus turns blue
No change in both.
Blue litmus turns red
Blue litmus remains blue

Validate

Solution:

Concept:

Burning sulphur produces sulphur dioxide, an acidic gas that forms sulphurous acid when mixed with water. Acids turn blue litmus red but do not affect red litmus.

Explanation:

Sulphur burns in air to give sulphur dioxide:

S + O_2 \to SO_2

This gas dissolves in water (e.g., moisture in the tumbler) to form sulphurous acid:

SO_2 + H_2O \to H_2SO_3

Sulphurous acid is acidic in nature.

Blue litmus paper changes to red in an acid; red litmus paper stays unchanged.

Therefore, when both litmus papers are placed in the tumbler, only the blue litmus turns red.

Answer:

C. Blue litmus turns red

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