JEE Main 2023 — Chemistry Physical Chemistry

2023integermedium

The specific conductance of $0.0025M$ acetic acid is $5\times {10}^{-5}S{\mathrm{cm}}^{-1}$ at a certain temperature. The dissociation constant of acetic acid is ___________ $\times {10}^{-7}$ .(Nearest integer)

Consider limiting molar conductivity of ${\mathrm{CH}}_{3}\mathrm{COOH}$ as $400S{\mathrm{cm}}^{2}{\mathrm{mol}}^{-1}$

Official previous-year question

Held on 10 Apr 2023 · Verified 6 Jul 2026.

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Solution

The relation between Molar conductance ${\lambda }_{m}$ and specific conductance $\kappa$ is

${\lambda }_{m}=\frac{k\times 1000}{M}$

M = molarity

${\lambda }_{m}=\frac{(5\times {10}^{-5})\times ({10}^{3})}{(2.5\times {10}^{-3})}=20S{\mathrm{cm}}^{2}{\mathrm{mol}}^{-1}$

Now, the degree of dissociation, $\alpha =\frac{{\lambda }_{m}}{{\lambda }^{\infty }}$

$\alpha =\frac{20}{400}=\frac{1}{20}$

The acid dissociation constant, ${K}_{a}=\frac{{C\alpha }^{2}}{(1-\alpha )}=\frac{(2.5\times {10}^{-3})(\frac{1}{20}\times \frac{1}{20})}{(\frac{19}{20})}$

$=65.789\times {10}^{–7}$

$\approx 66\times {10}^{–7}$

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JEE Main 2023 — Chemistry Physical Chemistry

2023integermedium

Consider limiting molar conductivity of ${\mathrm{CH}}_{3}\mathrm{COOH}$ as $400S{\mathrm{cm}}^{2}{\mathrm{mol}}^{-1}$

Official previous-year question

Held on 10 Apr 2023 · Verified 6 Jul 2026.

Did you get this right?

Solution

The relation between Molar conductance ${\lambda }_{m}$ and specific conductance $\kappa$ is

${\lambda }_{m}=\frac{k\times 1000}{M}$

M = molarity

${\lambda }_{m}=\frac{(5\times {10}^{-5})\times ({10}^{3})}{(2.5\times {10}^{-3})}=20S{\mathrm{cm}}^{2}{\mathrm{mol}}^{-1}$

Now, the degree of dissociation, $\alpha =\frac{{\lambda }_{m}}{{\lambda }^{\infty }}$

$\alpha =\frac{20}{400}=\frac{1}{20}$

The acid dissociation constant, ${K}_{a}=\frac{{C\alpha }^{2}}{(1-\alpha )}=\frac{(2.5\times {10}^{-3})(\frac{1}{20}\times \frac{1}{20})}{(\frac{19}{20})}$

$=65.789\times {10}^{–7}$

$\approx 66\times {10}^{–7}$

Your note

JEE Main Physical Chemistry in other years

Keep practicing Physical Chemistry

Work through every JEE Main Physical Chemistry PYQ, year by year.

Browse all Chemistry topics

JEE Main 2023 — Chemistry Physical Chemistry

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

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JEE Main 2023 — Chemistry Physical Chemistry

Did you get this right?

Solution

Your note

JEE Main Physical Chemistry in other years

More JEE Main Physical Chemistry questions

Other Chemistry topics for JEE Main

Organic Chemistry

Inorganic Chemistry

Keep practicing Physical Chemistry