The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant, Ka of the acid is :

Question

The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant, Ka of the acid is : (A) 3 × 10-1 (B) 1 ×10-3 (C) 1 × 10-5 (D) 1 × 107

Tardigrade Admin · Accepted Answer

underset0.1-xHQ leftharpoons undersetxH+ + undersetx Q- pH = 3, [H+] = 10-3, x = 10-3 Ka = ((x)× (x)/(0.1 - x)) = ((10-3)2/0.1-10-3) ≃ (10-6/0.1) = 10-5

Q. The pH of a $0.1$ molar solution of the acid $H Q$ is $3$ . The value of the ionization constant, $K_{a}$ of the acid is :

$3 \times 1 0^{- 1}$

$1 \times 1 0^{- 3}$

$1 \times 1 0^{- 5}$

$1 \times 1 0^{7}$

$0.1 - x H Q ⇌ x H^{+} + x Q^{-}$
$p H = 3, [H^{+}] = 1 0^{- 3}, x = 1 0^{- 3}$
$K_{a} = \frac{( x ) \times ( x )}{( 0.1 - x )} = \frac{( 1 0 ^{- 3} ) ^{2}}{0.1 - 1 0 ^{- 3}} ≃ \frac{1 0 ^{- 6}}{0.1} = 1 0^{- 5}$

Q. The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant, Ka​ of the acid is :

3×10−1

1×10−3

1×10−5

1×107