JEE Main 2019 — Chemistry Physical Chemistry

2019mcqhard

Liquids $A$ and $B$ form an ideal solution in the entire composition range. At $350K,$ the vapour pressure of pure A and pure B are $7\times {10}^{3}\mathrm{Pa}$ and $12\times {10}^{3}\mathrm{Pa}$ , respectively. The composition of the vapour in equilibrium with a solution containing 40 mole percent of A at this temperature is:

Official previous-year question

Held on 10 Jan 2019 · Verified 6 Jul 2026.

Options

A
${x}_{A}=0.4;{x}_{B}=0.6$
B
${x}_{A}=0.76;{x}_{B}=0.24$
C
${x}_{A}=0.28;{x}_{B}=0.72$
D
${x}_{A}=0.37;{x}_{B}=0.63$

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Solution

Since, ${P}_{A}^{0}=7\times {10}^{3}Pa; {P}_{B}^{0}=12\times {10}^{3}Pa$ and ${X}_{A}=0.4$ , ${X}_{B} =1-0.4=0.6$

According to Raoult's Law: ${P}_{T}={P}_{A}^{0}{X}_{A}+{P}_{B}^{0}{X}_{B}$

${P}_{T}=(7\times {10}^{3})(0.4)+(12\times {10}^{3})(0.6)$

${P}_{T}=10\times {10}^{3}Pa$

Now, ${P}_{A}^{0}{X}_{A}={P}_{T}{x}_{A}$

${x}_{A}=\frac{{P}_{A}^{0}{X}_{A}}{{P}_{T}}=\frac{7\times {10}^{3}\times 0.4}{{10}^{4}}\Rightarrow 0.28$

${x}_{B}=1-{x}_{A}\Rightarrow 1-0.28\Rightarrow 0.72$

Your note

JEE Main Physical Chemistry in other years

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JEE Main 2019 — Chemistry Physical Chemistry

2019mcqhard

Official previous-year question

Held on 10 Jan 2019 · Verified 6 Jul 2026.

Options

A
${x}_{A}=0.4;{x}_{B}=0.6$
B
${x}_{A}=0.76;{x}_{B}=0.24$
C
${x}_{A}=0.28;{x}_{B}=0.72$
D
${x}_{A}=0.37;{x}_{B}=0.63$

Did you get this right?

Solution

Since, ${P}_{A}^{0}=7\times {10}^{3}Pa; {P}_{B}^{0}=12\times {10}^{3}Pa$ and ${X}_{A}=0.4$ , ${X}_{B} =1-0.4=0.6$

According to Raoult's Law: ${P}_{T}={P}_{A}^{0}{X}_{A}+{P}_{B}^{0}{X}_{B}$

${P}_{T}=(7\times {10}^{3})(0.4)+(12\times {10}^{3})(0.6)$

${P}_{T}=10\times {10}^{3}Pa$

Now, ${P}_{A}^{0}{X}_{A}={P}_{T}{x}_{A}$

${x}_{A}=\frac{{P}_{A}^{0}{X}_{A}}{{P}_{T}}=\frac{7\times {10}^{3}\times 0.4}{{10}^{4}}\Rightarrow 0.28$

${x}_{B}=1-{x}_{A}\Rightarrow 1-0.28\Rightarrow 0.72$

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 2019 — 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

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Keep practicing Physical Chemistry

JEE Main 2019 — 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