Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	The ionisation of hydrogen sulphide in water is low in the presence of hydrochloric acid
Reason (R):	Hydrogen sulphide is a weak acid.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: Common ion effect

H₂S is a weak acid and forms an equilibrium in the solution. The reaction is as follows:

H_{2} S ⇌ 2 H^{+} + 2 S^{2 -}

When a strong acid like HCl is added to the solution, due to the common ion effect the ionization of H₂S is suppressed.

Hence, Both assertion and reason are true and the reason is not the correct explanation of assertion.