CBSE Class 12 · 2008 · All India · SolutionsShort Answer

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A solution containing 8 g of a substance in 100 g of diethyl ether boils at 36.86°C, whereas pure ether boils at 35.60°C. Determine the molecular mass of the solute. (For ether, K

_{b}

= 2.02 K kg mol

^{- 1}

)

Answer: M ≈ 128 g mol⁻¹

Solution

Elevation:

Δ T_{b} = 36.86 - 35.60 = 1.26 K

Molality:

m = \frac{1.26}{2.02} = 0.6238 mol kg^{- 1}

Moles in 100 g ether =

0.6238 \times 0.100 = 0.06238

mol.
Molar mass:

M = \frac{8}{0.06238}

M = 128.3 g mol^{- 1}

CBSE Class 12 Board · 2008 · All India · Subjective

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