Question

The density of 2 M aqueous solution of NaOH is 1.28 g/cm³. The molality of the solution is ______. [Given that molecular mass of NaOH = 40 g mol⁻¹]

Options

• 1.32 m

• 1.20 m

• 1.56 m

• 1.67 m

Answer 1

The density of 2 M aqueous solution of NaOH is 1.28 g/cm³. The molality of the solution is 1.67 m.

Explanation:

Given: Molarity (M) = 2 mol/L

Density (ρ) = 1.28 g/cm³ = 1280 g/L

Molar mass of NaOH = 40 g/mol

Mass of 1 L solution = 1280g

Mass of NaOH in 1 L = 2 mol × 40 = 80 g

Mass of water = 1280 − 80

= 1200 g

= 1.2 kg

`"Molality" = "moles of solute"/"kg of solvent"`

= `2/1.2`

= 1.67 mol/kg