Question

The equivalent conductance of an aqueous solution of $1.0283 \times 10^{-3} g$ equivalent acetic acid per litre is $48.15 \pi^{-1} cm ^{2}$ equiv $^{-1}$ at $25^{\circ} C$. At infinite dilution value is $390.7 \pi^{-1} cm ^{2}$ equiv $^{-1}$. Calculate the degree of ionisation and ionisation constant of acetic acid.

• A. $0.1232,1.78 \times 10^{-5}$
• B. $0.223,10.2 \times 10^{-5}$
• C. $0.229,1.78 \times 10^{-5}$
• D. $0.531,2.85 \times 10^{-5}$

Answer 1

Answer: (A)

$CH _{3} COOH + H _{2} O \rightleftharpoons CH _{3} COO ^{-}+ H _{3} O ^{+}$
(Degree of ionisation) $\alpha=\frac{\Lambda_{c}}{\Lambda_{0}}=\frac{48.15}{390.7}$
$=0.1232$
$K_{a}($ Ionisation constant $)=\frac{c \alpha^{2}}{1-\alpha}$
$=\frac{1.02 \times 10^{-3} \times(0.1232)^{2}}{(1-0.1232)}$
$=1.78 \times 10^{-5}$