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Chemistry · 2024 · 2 marks
CBSE 2024 · Region 4 · Set 2 · Q18
Calculate the molar mass of a compound when 6.3 g of it is dissolved in 27 g of chloroform to form a solution that has a boiling point of 68.04 °C.…
Calculate the molar mass of a compound when $\displaystyle 6.3$ g of it is dissolved in $\displaystyle 27$ g of chloroform to form a solution that has a boiling point of $\displaystyle 68.04$ °C. The boiling point of pure chloroform is $\displaystyle 61.04$ °C and $\displaystyle \mathrm{K}_{\mathrm{b}}$ for chloroform is $\displaystyle 3.63$ °C kg mol $\displaystyle { }^{-1}$.
Marking-scheme solution
\[\begin{aligned}
& \Delta T_{\mathrm{b}}=\mathrm{K}_{\mathrm{b}} m \\
& M_{B}=\frac{\mathrm{K}_{\mathrm{b}} \times w_{B} \times 1000}{\Delta T_{\mathrm{b}} \times W_{A}} \\
& M_{B}=\frac{3.63 \times 6.3 \times 1000}{7 \times 27} \\
& =121 \mathrm{~g} \mathrm{~mol}^{-1}
\end{aligned}
\]
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CBSE Class 12 Chemistry past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.