Question

Which one of the following procedures is correct to detect the acidic nature of SO₂ gas?
(1) Insert wet blue litmus paper in a gas jar filled with SO₂ gas
(2) Insert wet red litmus paper in a gas jar filled with SO₂ gas
(3) Insert dry blue litmus paper in a gas jar filled with SO₂ gas
(4) Insert dry red litmus paper in the gas jar filled with SO₂ gas

Answer 1

To detect the acidic nature of sulphur dioxide, we will place a wet blue litmus paper inside the gas jar. So, that wet litmus paper traps the gaseous SO₂ and converts the blue litmus to red.
We use wet litmus paper because when gas comes out, it can tested for acidity when they react with water in the litmus paper and form ions.

Hence, the correct answer is option 1.