Question

2 g of yellow sulphur powder is burnt in a china dish and the fumes are collected in a test tube. Water is added in the test tube and the solution is tested separately with blue and red litmus paper. The correct option is :

• A. Blue litmus remains blue and red litmus turns blue.
• B. Blue litmus turns red and red litmus remains red.
• C. Blue litmus turns red and red litmus turns blue.
• D. Blue litmus remains blue and red litmus remains red.

Hint:

Remember: Burning non-metals like sulphur forms acidic oxides that turn blue litmus red.

Answer 1

The Correct Option is B

When sulphur is burnt in air, it forms sulphur dioxide gas (SO$_2$): \[ S + O_2 \rightarrow SO_2 \] When SO$_2$ dissolves in water, it forms sulphurous acid (H$_2$SO$_3$), which is acidic: \[ SO_2 + H_2O \rightarrow H_2SO_3 \] An acidic solution turns blue litmus red but has no effect on red litmus paper. Therefore, the blue litmus will turn red and the red litmus will remain red.