Question

A compound H2X with molar weight 80g is dissolved in a solvent having density 0.4 g/ml.assuming no change in volume upon dissolution,the molality of a 3.2 molar solution

Answer 1

use the formula, M/m =weight of solvent /volume of solution.

as there is no change in volume, therefore volume of solution = volume of solvent now using the formula, you can get

3.2/0.4=m
therefore, m=8

Answer 2

Answer: The molality of a 3.2 molar solution is 8 mol/ kg.

Explanation:

$Molarity=\frac{\text{given mass of compound}}{\text{molar mass of compound}\times \text{volume of solution is L}}$

3.2 molar solution means that 3.2 moles are present in 1 L.

1L = 1000 mL

Given Density of the solvent:

$\frac{\text{mass of the solvent}}{\text{Volume of the solvent}}$

Mass of the solvent =$\text{density of the solvent} \times \text{volume of the solvent} =0.4g/ml\times 1000 mL=400 g=0.4 kg (1 kg=1000 g))$

$Molality=\frac{\text{given mass of compound}}{\text{molar mass of compound}\times \text{weight of solution is kg}}=\frac{\text{moles of compound}}{\text{weight of solution is kg}}$

$Molality=\frac{3.2}{0.4 kg}=8 mol/kg$

The molality of a 3.2 molar solution is 8 mol/ kg.