Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.
Assertion (A) : Aqueous solution of ammonium carbonate is basic.

Reason (R) : Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on Ka and Kb value of the acid and the base forming it.

Question

Note: In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.
Assertion (A) : Aqueous solution of ammonium carbonate is basic.

Reason (R) : Acidic/basic nature of a salt solution of a salt of weak acid and weak base depends on Ka and Kb value of the acid and the base forming it.

Philoid · Accepted Answer

Ammonium carbonate is a salt of weak acid and weak base.

H₂CO₃ + NH₄OH � (NH)₂CO₃

Weak acid weak base

pH = [ + - ]

Where, = -log (K_w)

K_w (ionic product of water)= 10^-14

= -log (10^-14) = 14

On comparing K_a and K_b of H₂CO₃ and NH₄OH,

K_a < K_b

On taking –log on both sides,

-log K_a > -log K_b

pK_a > pK_b

So, pK_a - pK_b > 0

Therefore, pH > [

i.e. pH > 7 which indicates basic solution.

From this it is clearly evident that acidic/basic nature of a solution of a salt of weak acid and weak base depends on K_a and K_b value of the acid and the base forming it.