Question

If the density of methanol is \(0.793\, \text{kg L}^{–1}\), what is its volume needed for making 2.5 L of its 0.25 M solution?

Answer 1

Molar mass of methanol \((\text{CH}_3\text{OH})\) = (1 × 12) + (4 × 1) + (1 × 16)

\(= 32 \text{g mol}^{-1}\)

\(= 0.032 \text{kg mol}^{-1}\)

Molarity of methanol solution \(= \frac{0.793 \text{kg L}^{-1} }{ 0.032 \text{kg mol}^{-1}}\)

\(= 24.78 \text{mol L}^{-1}\)

(Since density is mass per unit volume)

Applying, \(\text{M}_1\text{V}_1 = \text{M}_2\text{V}_2\)

(Given solution) (Solution to be prepared)

\((24.78\, \text{mol L}^{-1} ) V_1 = (2.5 \text{L}) (0.25 \text{mol L}^{-1} )\)

\(V_1 = 0.0252\, \text{L}\)

\(V_1 = 25.22\, \text{mL}\)