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Chemistry Β· 2026 Β· 3 marks
CBSE 2026 Β· Region 4 Β· Set 1 Β· Q26
Calculate the vapour pressure of a solution containing 61 g of benzoic acid (molar mass =122 g mol^-1 ) dissolved in 500 g of benzene when the vapourβ¦
Calculate the vapour pressure of a solution containing $\displaystyle 61$ g of benzoic acid (molar mass $\displaystyle =122 \mathrm{~g} \mathrm{~mol}^{-1}$ ) dissolved in $\displaystyle 500$ g of benzene when the vapour pressure of pure benzene at this temperature of experiment is $\displaystyle 66$ torr. Assume complete dimerization of benzoic acid in benzene.
Marking-scheme solution
π$\displaystyle 1$Β° βπ$\displaystyle 1$
π$\displaystyle 1$
Β°
= ππ₯$\displaystyle 2$ = π
π€$\displaystyle 2$Γπ$\displaystyle 1$
π$\displaystyle 2$Γπ€$\displaystyle 1$
$\displaystyle 66$βπ$\displaystyle 1$
= $\displaystyle 0.5$ Γ
π$\displaystyle 1$ = $\displaystyle 63.4$π‘πππ
Alternate method
π$\displaystyle 1$Β° βπ$\displaystyle 1$
π$\displaystyle 1$
Β°
= ππ₯$\displaystyle 2$ = π
π$\displaystyle 2$
π$\displaystyle 1$+ π$\displaystyle 2$
$\displaystyle 66$βπ$\displaystyle 1$
= $\displaystyle 0.5$ Γ
π$\displaystyle 1$ = $\displaystyle 63.61$π‘πππ
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSEβs own marking scheme gives it. Where our answers come from.