Calculate the molar mass of non volatile solute when 5 g of it is dissolved in 50 g solvent, boils at 119. 6 ∘ C . [ K b = 3.2 K kg mol − 1 , boiling point of pure solvent = 11 8 ∘ C ] .

Question

Calculate the molar mass of non volatile solute when 5 g of it is dissolved in 50 g solvent, boils at 119. 6 ∘ C . [ K b ​ = 3.2 K kg mol − 1 , boiling point of pure solvent = 11 8 ∘ C ] .

TestHub · Accepted Answer

The elevation in boiling point is given by $Δ T_{b} = T_{b} - T_{b}^{\circ}$

$Δ T_{b} = 119.6 - 118 = 1.6 K$

Using the formula for elevation in boiling point:

$Δ T_{b} = K_{b} \times m$

$Δ T_{b} = K_{b} \times \frac{w _{2} \times 1000}{M _{2} \times w _{1}}$

Substituting the given values:

$1.6 = 3.2 \times \frac{5 \times 1000}{M _{2} \times 50}$

$1.6 = 3.2 \times \frac{100}{M _{2}}$

$1.6 = \frac{320}{M _{2}}$

$M_{2} = \frac{320}{1.6} = 200 g mol^{- 1}$

Answer: $200 g mol^{- 1}$

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