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 (A) 13.88 × 10⁻²
(B) 13.88 × 10⁻¹
(C) 13.88 (D) 13.88 × 10⁻³

Answer 1

$\huge\bold{Answer}$

(C) 13.88 ❤✅⬆

......

Answer 2

The molality (in mol kg⁻¹) of the aqueous solution is (C) 13.88

-Mole fraction of solvent = 0.8

⇒Mole fraction of solute = 1 - mole fraction of solvent

                                         = 1 - 0.8 = 0.2

- Molality = No.of moles of solute / Weight of solvent in kg

           m = No.of moles of solute / (No.of moles of solvent × molar mass of solvent)

{because No of moles of solvent = Weight of solvent / Molar mass of solvent

⇒ Weight of solvent = No.of moles of solvent × molar mass of solvent }

         m = 0.2/(0.8 × 18/1000)  {here solvent is water, so molar mass = 18 gm}

         m = 200/14.4 = 13.88

- So the correct answer is option (C)