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An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute? - CBSE (Science) Class 12 - Chemistry

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Question

An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?

Solution

Here,

Vapour pressure of the solution at normal boiling point (p1) = 1.004 bar

Vapour pressure of pure water at normal boiling point (`p_1^0=1.013 " bar"`)

Mass of solute, (w2) = 2 g

Mass of solvent (water), (w1) = 98 g

Molar mass of solvent (water), (M1) = 18 g mol−1

According to Raoult’s law,

`(p_1^0-p_1)/p_1^0 = (w_2xxM_1)/(M_2xxw_1)`

`=>(1.013-1.004)/1.013=(2xx18)/(M_2xx98)`

`=>0.009/1.013 = (2xx18)/(M_2xx98)`

`=>M_2 = (1.013xx2xx18)/(0.009xx98)`

= 41.35 g mol-1

Hence, the molar mass of the solute is 41.35 g mol−1.

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Solution An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute? Concept: Vapour Pressure of Liquid Solutions - Vapour Pressure of Liquid- Liquid Solutions.
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