Question

A solution contains 20% solute by weight at ${60}^{\circ }$C. When cooled to ${30}^{\circ }$C, the solution contains 10% solute by weight. When 45 g solution is cooled from ${60}^{\circ }C$ to ${30}^{\circ }C$, the mass of solute deposited is :

• A. 4.5 g
• B. 4 g
• C. 5 g
• D. 4.75 g

Answer 1

Answer: (A)

4.5 g

$CaseI:$ (at ${60}^{\circ }C$)

Wt. % of solute at ${60}^{\circ }C$

$w_1$%$=20$

Weight of solute $=x=$?

Weight of solution $=$ 45 g

% by weight $=\frac{Weightofsolute}{Weightofsolution}\times 100$

$x=\frac{20\times 45}{100}=9g$

$CaseII:$ (at ${30}^{\circ }C$)

Wt.% of solute at ${30}^{\circ }C$

$=w_2$% $=10$

Weight of solute $=y=$?

Weight of solution $=45g$

% by weight $=\frac{Weightofsolute}{Weightofsolution}\times 100$

$y=\frac{10\times 45}{100}=4.5g$

Mass of solute deposited = 9 - 4.5 = 4.5 g

Hence, option (A) is the correct answer.