Question

Ethylene glycol, the primary ingredient in antifreeze, has the chemical formula C2H6O2. The radiator fluid used in most cars is a half-and-half mixture of water and antifreeze. Part A What is the freezing point of radiator fluid that is 50% antifreeze by mass? Kf for water is 1.86 ∘C/m. Part B What is the boiling point of radiator fluid that is 50% antifreeze by mass? Kb for water is 0.512 ∘C/m.

Answer 1

Let's consider 100 g of of the radiator fluid containing ethylene glycol.

mass f water = 50 g

mass of ethylene glycol = 50 g

Molecular mass of ethylene glycol(C2H6O2) = 62.07 g/mol

Hence moles of ethylene glycol = mass/molecular mass = 50 g / 62.07 g/mol = 0.80554 mol

Hence 0.80554 mol of ethylene glycol is present in 50 g of water

Molality is defined as the moles of solute present in 1000 g of the solvent.

Hence molality of the solution, m = (0.80554 mol / 50 g) x 1000 g = 16.11 m

(a): Kf = 1.86 ∘C/m.

Vant' Hoff for ethylene is 1

The depression in freezing point can be calculated as

Tf = i xKf x m = 1 x 1.86 ∘C/m x 16.11 m = 30.0 ∘C

=> Tf = Tf - 0 ∘C = 30.0 ∘C

=> Tf = - 30.0 ∘C (answer)

(b)

Kb = 0.512 ∘C/m.

Vant' Hoff for ethylene is 1

The depression in freezing point can be calculated as

Tb = i xKb x m = 1 x 0.512 ∘C/m x 16.11 m = 8.25 ∘C

=> Tb = Tb - 100 ∘C = 8.25 ∘C

=> Tb = 108.25 ∘C (answer)