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A bottle is labelled sodium hydroxide, 3.0 M, density 1.11 g mL⁻¹.

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A bottle is labelled sodium hydroxide, $3.0\ \text{M}$ , density $1.11\ \text{g mL}^{-1}$ . Find the mass of water in one litre of the solution, and the molality. Sodium hydroxide is $40\ \text{g mol}^{-1}$ .

Need a reminder? The key ideaShow

Mass percent $= \dfrac{\text{mass of solute}}{\text{mass of solution}} \times 100$ . Mole fraction $x_A = \dfrac{n_A}{n_A + n_B}$ . Molarity $= \dfrac{\text{mol of solute}}{\text{L of solution}}$ . Molality $= \dfrac{\text{mol of solute}}{\text{kg of solvent}}$ , which does not change with temperature. The density links the two: one litre of solution has a mass of $1000 \times d$ grams, with $d$ in $\text{g mL}^{-1}$ .

The worked solution

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← Antifreeze has ethylene glycol, C₂H₆O₂ (62 g mol⁻¹), dissolved in water.Concentrated sulphuric acid is 98% H₂SO₄ by mass, and its density is 1.84 g mL⁻¹. →

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A bottle is labelled sodium hydroxide, 3.0 M, density 1.11 g mL⁻¹.

The worked solution

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