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Q28
(NDA-I/2011)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles
Answer Verified
A student heated some sulphur in a spatula and collected the gas ‘X’. Which one among the following is correct about ‘X’ ?
Result
Your answer:
—
·
Correct:
C
Explanation
The correct answer is Option 3. When sulphur is heated in the presence of atmospheric oxygen, it undergoes a combustion reaction to form Sulphur Dioxide (SO₂) gas. The chemical equation is: S + O₂ → SO₂.
The nature of the gas 'X' (SO₂) is determined by its reaction with water:
- Chemical Nature: Sulphur dioxide is a non-metallic oxide. Most non-metallic oxides are acidic in nature.
- Reaction with Moisture: When SO₂ comes into contact with moist litmus paper, it reacts with the water to form Sulphurous acid (H₂SO₃).
- Indicator Change: Since an acid is formed, it turns moist blue litmus paper to red.
Why other options are incorrect: Option 1 is wrong because acidic gases do not turn litmus blue. Option 2 is incorrect due to the chemical formula (SO,,). Option 4 is wrong because dry litmus does not react with SO₂ as moisture is essential for the formation of ions that cause the color change.
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