Question

Write the definition of molality. 1/10 mole of a solute is dissolved in 100 g solvent. Calculate the molality of the solution.

Hint:

Molality depends only on mass of solvent (kg), not on volume. Hence, unlike molarity, it is independent of temperature.

Answer 1

Definition:
Molality (\(m\)) is defined as the number of moles of solute present in 1 kilogram of solvent.
\[ m = \frac{n_{\text{solute}}}{w_{\text{solvent}}(\text{in kg})} \] Given:
Moles of solute = \( \tfrac{1}{10} = 0.1\ \text{mol} \).
Mass of solvent = \(100\ \text{g} = 0.100\ \text{kg}\).

Step 1: Calculate molality.
\[ m = \frac{0.1}{0.100} = 1.0\ \text{mol kg}^{-1} \] \[ \boxed{\text{Molality of the solution } = 1.0\ \text{m}} \]