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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 2 · Set 2 · Q22
A solution containing 8.0 g of a non-volatile solute in 100 g of diethyl ether boils at 36.86 °C whereas pure diethyl ether boils at 35.60 °C.…
A solution containing $\displaystyle 8.0$ g of a non-volatile solute in $\displaystyle 100$ g of diethyl ether boils at $\displaystyle 36.86$ °C whereas pure diethyl ether boils at $\displaystyle 35.60$ °C. Determine the molar mass of the solute. \[\left(\mathrm{K}_{\mathrm{b}} \text { for diethyl ether }=2.02 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right) \]
Marking-scheme solution
ΔTb = Tb − T°b = $\displaystyle 36.86$ − $\displaystyle 35.60$ = $\displaystyle 1.26$ 0C
Δ𝑇𝑏= 𝐾𝑏
𝑊𝐵
𝑀𝐵𝑋
𝑊𝐴
or M𝐵= $\displaystyle 2.02$ 𝑋
$\displaystyle 1.26$ 𝑋 $\displaystyle 1000$
=$\displaystyle 16160$
= $\displaystyle 128.25$ g mol−$\displaystyle 1$
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.