Question

A solution containing 2.5 × 10⁻³ kg of a solute dissolved in 75 × 10⁻³ kg of water, boils at 373.535 K. The molar mass of solute is ______ g mol⁻¹. (Nearest integer)

(Given: k_b (H₂O) = 0.52 K molal⁻¹, boiling point of water = 373.15 K)

Answer 1

A solution containing 2.5 × 10⁻³ kg of a solute dissolved in 75 × 10⁻³ kg of water, boils at 373.535 K. The molar mass of solute is 45 g mol⁻¹.

Explanation:

Given: Mass of solute w₂ = 2.5 × 10⁻³ kg

Mass of water w₁ = 75 × 10⁻³ kg

Boiling point of solution = 373.535 K

Boiling point of water = 373.15 K

Boiling point elevation ΔT_b = 373.535 − 373.15 = 0.385 K

K_b = 0.52. K molal⁻¹

`Delta T_b = (w_2 * K_b * 1000)/(M * w_1)`

`M = (w_2 * K_b * 1000)/(Delta T_b * w_1)`

`M = (2.5 xx 0.52 xx 1000)/(0.385 xx 75)`

`M = 1300/28.875`

M = 45.02 

M = 45 g/mol