Question

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

Answer 1

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

Step-by-step explanation:

Assume 100 g of solution.

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

`\text{Molal concentration} = \frac{\text{moles of solute}}{\text{kilograms of solvent}}`

1. Moles of NaCl

`\text{Moles of NaCl} = \text{10.0 g NaCl} * \frac{\text{1 mol NaCl}}{\text{58.44 g NaCl}} = \text{0.1711 mol NaCl}`

2. Kilograms of water

`\text{Kilograms} = \text{90.0 g} * \frac{\text{1 kg}}{\text{1000 g}} = \text{0.0900 kg}`

3. Molal concentration

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