Question

3. What is the boiling point of an antifreeze/coolant solution made from a 40% mixture of ethylene glycol (CHO) in water? Density of CHO is 1.11 g/mL and its molar mass is 62.07 g/mol. Kb= 0.52°C/m Answer: 106.2°C

Answer 1

40% mixture of ethylene glycol in water means in every 100 mL solution, there is 40 mL ethylene glycol and 60 mL water.

Density of ethylene glycol=1.11 g/mL

Mass of ethylene glycol added=Density x Volume

=1.11 g/mL x 40 mL

=44.4 g

Molar mass of ethylene glycol=62.07 g/mol

So number of moles of ethylene glycol (solute)

=Mass/molar mass

=44.4 g/62.07 g/mol

=0.72 mol

Mass of water (solvent) in the mixture=Density of water x Volume of water

=1 g/mL x 60 mL

=60 g

=60 g/1000 g/kg (1 kg=1000 g)

=0.06 kg

Molality of the mixture=number of moles of solute/mass of solvent (kg)

=0.72 mol/0.06 kg

=12 m

Boiling point of pure water=T_i=100°C

Elevation in boiling point of the mixture=∆T_b=K_b x m

T_f - T_i=K_b x m

T_f​​​​​​ -100°C=0.52°C/m x 12 m

T_f=0.52°C/m x 12 m + 100°C

T_f=6.24°C + 100°C=106.24°C

So boiling point of the antifreeze/coolant solution=106.24°C