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. What is the freezing point of radiator fluid that is 50% antifreeze by mass? The Kf for water is 1.86oC/m.  

Answer 1

Solution :-

lets assume we have 100 g of the antifreez mixture

then mass of water = 50 g = 0.05 Kg

mass of ethylene glycol = 50 g

lets calculate the moles of ethylene glycol

moles of ethylene glycol = 50 g / 62.07 g per mol = 0.79745 mol

now lets calculate the molality of the solution

molality = moles / kg solvent

            = 0.79745 mol / 0.05 kg

            = 15.95 m

now lets calculate the change in the freezing point

Delta Tf = Kf * m

Kf = 1.86 C/m for water

Delta Tf = 1.86 C /m * 15.95 m

             = 29.7 C

So the freezing point of the solution = freezing point of pure water - delta Tf

                                                        = 0 C - 29.7 C

                                                        = - 29.7 C

So the freezing point of the radiator fluid = -29.7 ^oC or we can round it to - 30 ^oC