Question

At ${25}^{\circ }C$ molar conductance of $0.1$ molar aqueous solution of ammonium hydroxide is $9.52$ ${\text{ohm}}^{-1}{\text{cm}}^2{\text{mol}}^{-1}$ and at infinite dilution its molar conductance is $238$ ${\text{ohm}}^{-1}{\text{cm}}^2{\text{mol}}^{-1}$. The percentage degree of dissociation of ammonium hydroxide at the same concentration and temperature is:
[1 Mark]

• A. $4\%$
• B. $40\%$
• C. $20\%$
• D. $2\%$

Answer 1

The correct option is A $4\%$

Let,
${\Lambda }_m^C=\text{Molar conductivity at concentration C (0.1 molar)}$
${\Lambda }_m^{\infty }=\text{Molar conductivity at infinite dilution}$
Degree of dissociation
$\alpha =\frac{{\Lambda }_m^C}{{\Lambda }_m^{\infty }}$
$\Rightarrow \alpha =\frac{9.52{\Omega }^{-1}{\text{cm}}^2{\text{mol}}^{-1}}{238{\Omega }^{-1}{\text{cm}}^2{\text{mol}}^{-1}}=0.04=4\%$