Question

What is the relative lowering of a vapour pressure of 26% solution of a non-volatile solute (MW=52) in diethyl ether?

• A. $0.5$
• B. $0.33$
• C. $0.25$
• D. $0.125$

Answer 1

Answer: (B)

$0.33$

Diethyl ether $=(C_2{H}_5{)}_{2}O$

$M.\omega t=74$

$26$% $\left(\omega /\omega \right)=26$ gm solute in 100 gm solution

Solvent $=100-26=74gm$

$n_{solute}=\frac{26}{52}=0.5$

$n_{solvent}=\frac{74}{74}=1$

$X_{solute}=\frac{0.5}{1+0.5}=\frac{1}{3}$

So relative lowering of pressure, $\frac{\Delta P}{P_{Ao}}=X_{solute}$

$=\frac{1}{3}=0.33$