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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

ConceptVapour Pressure of Liquid Solutions Vapour Pressure of Liquid- Liquid Solutions

#### 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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