Question

Equivalent conductance of $0.05N$ solution of acetic acid is $7.36Sc{m}^2$ at $25^{\circ }C$. What is the value of $K_a$ for this acetic acid solution if equivalent conductance of acetic acid at infinite dilution is $390.7Sc{m}^2$?

• A. $9.4\times 10^{-4}$
• B. $7.1\times 10^{-4}$
• C. $1.77\times 10^{-5}$
• D. $4.7\times 10^{-5}$

Answer 1

Answer: (C)

Degree of dissociation
$\left(\alpha \right)=\frac{{\wedge }_m^c}{{\wedge }_m^{\circ }}$
For monobasic acetic acid, molar conductance = equivalent conductance
$\therefore \alpha =\frac{7.36}{390.7}=1.88\times 10^{-2}$
For weak acid solution dissociation constant $\left(K\right)=C{\alpha }^2$
$=0.05{\left(1.88\times 10^{-2}\right)}^2=1.77\times 10^{-5}$