When 9.45g of ClCH_2 COOH is… - JEE Main 2021 Chemistry PYQ

JEE Main 2021 — Chemistry Physical Chemistry

2021integermedium

When $9.45g$ of ${\mathrm{ClCH}}_{2}\mathrm{COOH}$ is added to $500\mathrm{mL}$ of water, its freezing point drops by $0.5^{\circ}C.$ The dissociation constant of ${\mathrm{ClCH}}_{2}\mathrm{COOH}$ is $x\times {10}^{-3}.$ The value of $x$ is off to the nearest integer)

$[{K}_{f({H}_{2}O)}=1.86K\mathrm{kg}{\mathrm{mol}}^{-1}]$

Official previous-year question

Held on 24 Feb 2021 · Verified 6 Jul 2026.

Did you get this right?

Solution

${\mathrm{ClCH}}_{2}\mathrm{COOH}\rightleftharpoons {\mathrm{ClCH}}_{2}{\mathrm{COO}}^{\ominus }+{H}^{+}$

$i=1+(2-1)\alpha$

$i=1+\alpha$

${\Delta T}_{f}=i.{K}_{f}.m$

$0.5=(1+\alpha )(1.86)(\frac{(\frac{9.45}{94.5})}{(\frac{500}{1000})})$

$\frac{5}{3.72}=1+\alpha \Rightarrow \alpha =\frac{1.28}{3.72}$

$\alpha =\frac{32}{93}$

JEE Main 2021 Chemistry, Solutions — solution figure

${K}_{a}=\frac{{(C\alpha )}^{2}}{C-C\alpha }=\frac{C{\alpha }^{2}}{1-\alpha } C=\frac{0.1}{500/1000}=0.2$

${K}_{a}=\frac{0.2{(32/93)}^{2}}{(1-32/93)}=\frac{0.2\times {(32)}^{2}}{93\times 61}$

$=0.036$

${K}_{a}=36\times {10}^{-3}$

Your note

JEE Main Physical Chemistry in other years

Physical Chemistry 2026 Physical Chemistry 2025 Physical Chemistry 2024 Physical Chemistry 2023 Physical Chemistry 2022 Physical Chemistry 2020 Physical Chemistry 2019 Physical Chemistry 2018 Physical Chemistry 2017 Physical Chemistry 2016 Physical Chemistry 2015 Physical Chemistry 2014

More JEE Main Physical Chemistry questions

80 mL of a hydrocarbon on mixing with 264 mL of oxygen in a closed U-tube undergoes complete combustion. The residual gases after cooling to 273 K occupy 224 mL. When the system is treated with KOH solution, the volume decreases to 64 mL. The formula of the hydrocarbon is :

2026hard

What is the energy (in J atom$^{-1}$) required for the following process? $Li^{2+}(g) \rightarrow Li^{3+}(g) + e^-$ (Take the ionization energy for the H atom in the ground state as $2.18 \times 10^{-18}$ J atom$^{-1}$)

2026medium

Consider the following reduction processes : $\mathrm{Al}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Al}(\mathrm{s}), \mathrm{E}^{0}=-1.66 \mathrm{~V}$ $\mathrm{Fe}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Fe}^{2+}, \mathrm{E}^{0}=+0.77 \mathrm{~V}$ $\mathrm{Co}^{3+}+\mathrm{e}^{-} \longrightarrow \mathrm{Co}^{2+}, \mathrm{E}^{0}=+1.81 \mathrm{~V}$ $\mathrm{Cr}^{3+}+3 \mathrm{e}^{-} \longrightarrow \mathrm{Cr}(\mathrm{s}), \mathrm{E}^{\circ}=-0.74 \mathrm{~V}$ The tendency to act as reducing agent decreases in the order :

2026medium

X and Y are the number of electrons involved, respectively during the oxidation of $\mathrm{I}^{-}$to $\mathrm{I}_{2}$ and $\mathrm{S}^{2-}$ to S by acidified $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$. The value of $\mathrm{X}+\mathrm{Y}$ is $\_\_\_\_$.

2026medium

Identify the correct statements from the following: A. Heisenberg uncertainty principle is applicable to electrons. B. The size of $2p_x$ orbital is less than the size of $3p_x$ orbital. C. The energy of $2s$ orbital of H atom is equal to the energy of $2s$ orbital of Li. D. The electronic configuration of Cr is $[\text{Ar}] 3d^5 4s^1$ Choose the correct answer from the options given below:

2026medium

View all Physical Chemistry questions

Keep practicing Physical Chemistry

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

Browse all Chemistry topics

Solution

${\mathrm{ClCH}}_{2}\mathrm{COOH}\rightleftharpoons {\mathrm{ClCH}}_{2}{\mathrm{COO}}^{\ominus }+{H}^{+}$

$i=1+(2-1)\alpha$

$i=1+\alpha$

${\Delta T}_{f}=i.{K}_{f}.m$

$0.5=(1+\alpha )(1.86)(\frac{(\frac{9.45}{94.5})}{(\frac{500}{1000})})$

$\frac{5}{3.72}=1+\alpha \Rightarrow \alpha =\frac{1.28}{3.72}$

$\alpha =\frac{32}{93}$

JEE Main 2021 Chemistry, Solutions — solution figure

${K}_{a}=\frac{{(C\alpha )}^{2}}{C-C\alpha }=\frac{C{\alpha }^{2}}{1-\alpha } C=\frac{0.1}{500/1000}=0.2$

${K}_{a}=\frac{0.2{(32/93)}^{2}}{(1-32/93)}=\frac{0.2\times {(32)}^{2}}{93\times 61}$

$=0.036$

${K}_{a}=36\times {10}^{-3}$

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

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