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Depression in Freezing Point

By dissolving...

Question

By dissolving 13.6 g of a substance in 20 g of water, the freezing point decreased by ${3.7}^{o} C$ . Calculate the molecular mass of the substance.
(Molal depression constant for water = 1.863 K kg mol $^{- 1}$ )

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Solution

We have,

$Δ T_{f} = \frac{1000 \times K_{f} \times w}{M \times W}$

$3.7 = 1000 \times 1.863 \times \frac{13.6}{M \times 20}$

Molecular mass of substance, $M = 342 g m o l^{- 1}$

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