The vapour pressure of acetone at 20°C is 185 torr. When 1.2 g of a non-volatile substance was dissolved in 100 g of acetone at 20°C, its vapour pressure was 183 torr. The molar mass (g mol

Engineering

Chemistry

Relative Lowering in Vapour Pressure

Question

The vapour pressure of acetone at 20°C is 185 torr. When 1.2 g of a non-volatile substance was dissolved in 100 g of acetone at 20°C, its vapour pressure was 183 torr. The molar mass (g mol^–1) of the substance is :

488

128

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$(D) \frac{P_{A}^{o} - P_{S}}{P_{S}} = \frac{n_{B}}{n_{A}}$

$\frac{185 - 183}{183} = \frac{1 .2 \times 58}{M \times 100}$

M = 64