Question

A solution contains 6.21 g of ethylene glycol dissolved in 25.0 g of water. If water has a boiling point elevation constant of 0.512°C•kg/mol, what is the boiling point of the solution? (molar mass of ethylene glycol = 62.1 g/mol; boiling point of pure water = 100.00°C)

Answer 1

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Answer 2

Calculate first the number of moles of ethylene glycol by dividing the mass by the molar mass.
                           n = (6.21 g ethylene glycol) / 62.1 g/mol
                              n = 0.1 mol
Then, calculate the molality by dividing the number of moles by the mass of water (in kg).
                           m = 0.1 mol/ (0.025 kg) = 4m
Then, use the equation,
                       Tb,f = Tb,i + (kb)(m)
Substituting the known values,
                       Tb,f = 100°C + (0.512°C.kg/mol)(4 mol/kg)
                          Tb,f = 102.048°C