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The Vapour Pressure of Water is 12.3 Kpa at 300 K. Calculate Vapour Pressure of 1 Molal Solution of a Non-volatile Solute in It. - CBSE (Science) Class 12 - Chemistry

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Question

The vapour pressure of water is 12.3 kPa at 300 K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.

Solution

1 molal solution means 1 mol of the solute is present in 1000 g of the solvent (water).

Molar mass of water = 18 g mol−1

∴Number of moles present in 1000 g of water  = `1000/18`

= 55.56 mol

Therefore, mole fraction of the solute in the solution is

`x_2= 1/(1+55.56)= 0.0177`

Vapour pressure of water,  `p_1^0     =12.3 kPa`

Applying the relation,  `(p_1^0-p_1)/p_1^0 = x_2`

`=> (12.3- p_1)/12.3 = 0.0177`

`=>12.3 - p_1 =  0.2177`

= 12.08 kPa (approximately)

Hence, the vapour pressure of the solution is 12.08 kPa.

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Solution The Vapour Pressure of Water is 12.3 Kpa at 300 K. Calculate Vapour Pressure of 1 Molal Solution of a Non-volatile Solute in It. Concept: Vapour Pressure of Liquid Solutions - Vapour Pressure of Liquid- Liquid Solutions.
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