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Depression in Freezing Point

1.355 g of a ...

Question

1.355 g of a substance dissolved in 55 g of $C H_{2} C O O H$ produced a depression in the freezing point of ${0.618}^{o} C$ . Calculate the molecular weight of the substance. $(K_{f} = 3.85)$

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Solution

$△ T = K_{f} \times \frac{w_{B} \times 1000}{m_{B} \times w_{A}}$
where, $w_{B} =$ mass of solute, $m_{B} =$ molar mass of solute, $w_{A} =$ mass of solvent
$0.618 = 3.85 \times \frac{1.355 \times 1000}{m_{B} \times 55}$
$m_{B} = 153.47 g / m o l$

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