Question

Calculate the molality of a 20% $CaC{O}_3$ solution (by mass). The density of the solution is 1.2 g/mL.

• A. 1.25 m
• B. 2.50 m
• C. 2.08 m
• D. 1.52 m

Answer 1

The correct option is B 2.50 m

Let the mass of the solution be 100 g.
Mass of $CaC{O}_3$
$=20$ g
Mass of water = 80 g
Moles of $CaC{O}_3$
$=\frac{\text{given mass}}{\text{Molar mass}}=\frac{20}{100}=0.2$
$Molality=\frac{\text{moles of solute}}{\text{weight of solvent (g)}}\times 1000$$=\frac{0.2}{80}\times 1000$

$Molality=2.5m$