Question

Hexachlorophene is used as a disinfectant in germicidal soaps. What mass of hexachlorophene ( = 406.9 g/mol) must be added to 125 g of chloroform to give a solution with a boiling point of 62.60°C?
Kb = 3.63°C/m, boiling point of pure chloroform = 61.70°C
please provide me with right solution with detailed steps.

Answer 1

Mass of solvent(chloroform) = 125 g x ( 1 kg/1000 g) = 0.125 kg

Boiling point of solvent (chloroform) = 61.70 ^oC

Boiling point of solution = 62.60 ^oC

K_b value for chloroform = 3.63 ^oC/m

Molar mass of hexachlorophene = 406.9 g/mol

The formulae to determine the boiling point elevation are as follows:

T_b = i x K_b x m -------- (1)

Here, elevation in the boiling point of the solution is T_b , boiling point constat is K_b,Van't Hoff factor is "ï", molality is "m".

T_b = Boiling point of the solution - Boiling point of solvent -------(2)

Use formula (2) and determine the elevation in the boiling point of the solution as follows:

T_b = 62.60 ^oC - 61.70 ^oC

T_b = 0.9 ^oC

Rearrange the formula (2) for molality(m) as follows:

Molality(m) = T_b /(i x K_b) ----------(3)

For Hexachlorophene, van't Hoff factor(i) is 1. Since van't Hoff factor for non-volatile solute is 1.

Substitute 0.9 ^oC for T_b , 1 for i, 3.63 ^oC/m for K_b in rearranged equation (3) and determine the value of molality as follows:

Molality(m) = 0.9 ^oC /(1 x 3.63 ^oC/m)

Molality(m) = 0.2479 m

Use the molality and mass of the solvent(chloroform). Determine the moles of hexachlorophene as follows:

The formula to determine molality is as follows:

Molality = Moles of solute / Kg of solvent

Rearrange the formula for moles of solute as follows:

Moles of solute = Molality x Kg of solvent

Substitute 0.2479 m for molality and 0.125 kg for Kg of solvent. Determine the moles of solute as follows:

Moles of solute = 0.2479 m x 0.125 kg

Moles of solute = 0.03099 mol hexachlorophene

Use the moles of hexachlorophene and molar mass. Determine the mass of hexachlorophene as follows:

The molar mass of hexachlorophene = 406.9 g/mol

Thus,

= 0.03099 mol hexachlorophene x ( 406.9 g hexachlorophene / 1 mol hexachlorophene)

= 12.6 g hexachlorophene

Thus mass of hexachlorophene must be added = 12.6 g [3 S.F]