Question

$12g$ of urea is present in $1$ litre of solution and $68.4g$ of sucrose is separately dissolved in $1$ litre of another sample of solution. The lowering of vapour pressure of first solution is :

• A. Equal to second
• B. Greater than second
• C. Less than second
• D. Double that of seconds

Answer 1

The correct option is A Equal to second

Moles of urea $=12/60=0.2$

Moles of sucrose $=68.4/342=0.2$

(Molar mass of sucrose is 342gm )

Since there are equal moles of solute in equal volumes of water, the mole fraction is the same.

As per Raoult's law, the relative lowering of pressure is also the same.