Question

The density of a 6 M solution of sodium chloride is 1.525 g/mL. Calculate the molality of the solution.

• A. 1.18 m
• B. 2.42 m
• C. 5.11 m
• D. 3.79 m

Answer 1

The correct option is C 5.11 m

Let the volume of the solution be 100 mL
Molarity = $\frac{\text{number of moles of solute}}{\text{volume of the solution in mL}}\times 1000$
6 = $\frac{\text{number of moles of solute}}{\text{100}}\times 1000$
Number of moles = 0.6 mol
Mass of solute = 0.6 $\times 58.5$ = 35.1 g
Since, Density = $\frac{\text{mass of solution}}{\text{volume of the solution}}$
Mass of the solution = $1.525\times 100$ = 152.5 g
Mass of solvent = 152.5 - 35.1 g = 117.4 g
Molality = $\frac{\text{moles of solute}}{\text{mass of solvent in g}}\times 1000$
Molality = $\frac{0.6}{117.4}\times 1000$ = 5.11 m