Question

The mole fraction of a solvent in aqueous solution of a solute is 0.8. The molality (in mol kg⁻¹) of the aqueous solution is ______.

Options

• 13.88 × 10⁻¹

• 13.88 × 10⁻³

• 13.88

• 13.88 × 10⁻²

Answer 1

The mole fraction of a solvent in aqueous solution of a solute is 0.8. The molality (in mol kg⁻¹) of the aqueous solution is 13.88.

Explanation:

Given: Mole fraction of solvent `(chi_"solvent") = 0.8`

Mole fraction of solute `(chi_"solute") = 1 − 0.8 = 0.2`

Let the total number of moles = 1

So,

Moles of solute = 0.2

Moles of solvent = 0.8

Molar mass of solvent = 18 g/mol

Mass = 0.8 × 18 = 14.4 g = 0.0144 kg

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

= `0.2/0.0144`

= 13.88 mol/kg