JEE Main 2015 — Chemistry Physical Chemistry

2015mcqmedium

The vapour pressure of acetone at ${20}^{o}C$ is $185\mathrm{torr}$ . When $1.2g$ of a non-volatile substance was dissolved in $100g$ of acetone at ${20}^{o}C$ , its vapour pressure was $183\mathrm{torr}$ . The molar mass $(g mo{l}^{-1})$ of the substance is:

Official previous-year question

Held on 4 Apr 2015 · Verified 6 Jul 2026.

Options

A
$488$
B
$32$
C
$64$
D
$128$

Did you get this right?

Solution

$\Delta \text{P} = 1 8 5 - 1 8 3 = \text{2 torr}$

${\text{M}}_{{\text{CH}}_{3}-\underset{\overset{||}{\text{O}}}{\text{C}}-{\text{CH}}_{3}}=15\times 2+16+12=\text{58 g/mol}$

$\frac{\Delta \text{P}}{{\text{P}}^{0}}=\frac{185-183}{185}=\frac{2}{185}={\text{X}}_{\text{B}}=\frac{\frac{\text{1.2}}{\text{M}}}{(\frac{\text{1.2}}{\text{M}})+\frac{100}{58}}$

$\frac{ \text{1.2} }{ \text{M} } \text{<<} \frac{ 1 0 0 }{ 5 8 }$

$\Rightarrow \frac{ 2 }{ 1 8 5 } = \frac{ \text{1.2} }{ \text{M} } \times \frac{ 5 8 }{ 1 0 0 }$

$\text{M} = \frac{ 5 8 \times \text{1.2} }{ 1 0 0 } \times \frac{ 1 8 5 }{ 2 }$

$=\text{64.38}\approx \text{64 g/mol}$

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JEE Main 2015 — Chemistry Physical Chemistry

2015mcqmedium

Official previous-year question

Held on 4 Apr 2015 · Verified 6 Jul 2026.

Options

A
$488$
B
$32$
C
$64$
D
$128$

Did you get this right?

Solution

$\Delta \text{P} = 1 8 5 - 1 8 3 = \text{2 torr}$

${\text{M}}_{{\text{CH}}_{3}-\underset{\overset{||}{\text{O}}}{\text{C}}-{\text{CH}}_{3}}=15\times 2+16+12=\text{58 g/mol}$

$\frac{\Delta \text{P}}{{\text{P}}^{0}}=\frac{185-183}{185}=\frac{2}{185}={\text{X}}_{\text{B}}=\frac{\frac{\text{1.2}}{\text{M}}}{(\frac{\text{1.2}}{\text{M}})+\frac{100}{58}}$

$\frac{ \text{1.2} }{ \text{M} } \text{<<} \frac{ 1 0 0 }{ 5 8 }$

$\Rightarrow \frac{ 2 }{ 1 8 5 } = \frac{ \text{1.2} }{ \text{M} } \times \frac{ 5 8 }{ 1 0 0 }$

$\text{M} = \frac{ 5 8 \times \text{1.2} }{ 1 0 0 } \times \frac{ 1 8 5 }{ 2 }$

$=\text{64.38}\approx \text{64 g/mol}$

Your note

JEE Main Physical Chemistry in other years

Keep practicing Physical Chemistry

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

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JEE Main 2015 — Chemistry Physical Chemistry

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Solution

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JEE Main Physical Chemistry in other years

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Organic Chemistry

Inorganic Chemistry

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JEE Main 2015 — Chemistry Physical Chemistry

Options

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