Question

What is the boiling point of a mixture composed of 85.0 g HOCH2CH2OH (ethylene glycol) and 185 g H2O? The boiling point elevation constant for H2O is 0.512 °C/m.

Answer 1

Answer – We are given, Kb = 0.512 °C/m,   mass of HOCH2CH2OH = 85.0 g , mass of water = 185 g

Normal boiling point of water, H2O = 100.00 °C

Molar mass of HOCH2CH2OH = 62.07 g/mol

First we need to calculate the moles of ethylene glycol

Moles of HOCH2CH2OH = 85 g / 62.07 g.mol^-1

                                           = 1.37 moles

Molality of HOCH2CH2OH = 1.37 moles / 0.185 kg

                                                = 7.40 m

We know,

∆Tb = Kb*m

      = 0.512 °C/m*7.40 m

     = 3.79 ^oC

boiling point of the solution = pure solvent boiling point +∆Tb

                                             = 100 + 3.79

                                             = 103.8^oC

So, the boiling point of a mixture composed of 85.0 g HOCH2CH2OH (ethylene glycol) and 185 g H2O is 103.8^oC