Question

Calculate the molality of a 10.0% by mass solution of NaCl ______ m

Answer 1

Answer:

$\large \boxed{\text{0.180 mol/kg }}$

Explanation:

Assume 100 g of solution.

Then you have 10.0 g of NaCl and 90.0 g of water.

$\text{Molal concentration} = \dfrac{\text{moles of solute}}{\text{kilograms of solvent}}$

1. Moles of NaCl

$\text{Moles of NaCl} = \text{10.0 g NaCl} \times \dfrac{\text{1 mol NaCl}}{\text{58.44 g NaCl}} = \text{0.1711 mol NaCl}$

2. Kilograms of water

$\text{Kilograms} = \text{90.0 g} \times \dfrac{\text{1 kg}}{\text{1000 g}} = \text{0.0900 kg}$

3. Molal concentration

$\text{Molal concentration} = \dfrac{\text{0.1711 mol}} {\text{0.0900 kg}} = \textbf{1.90 mol/kg}\\\\\text{The molal concentration of the solution is \large \boxed{\textbf{0.180 mol/kg }} }$