A 50/50 blend of engine coolant and water (by volume) is usually used in an auto

Question

A 50/50 blend of engine coolant and water (by volume) is usually used in an automobile's engine cooling system. If your car's cooling system holds 5.50 gallons, what is the boiling point of the solution? Make the following assumptions in your calculation: at normal filling conditions, the densities of engine coolant and water are 1.11 g/mL and 0.998 g/mL respectively. Assume that the engine coolant is pure ethylene glycol (HOCH_2CH_2OH), which is non-ionizing and non-volatile, and that the pressure remains constant at 1.00 atm. Also, you'll need to look up the boiling-point elevation constant for water.

Explanation / Answer

volume of water = volume of ethylene glycol

                          = 1/2 x 5.50

                          = 2.75 gal

                          = 10409.88 mL

mass of water = 10409.88 x 0.998

                       = 10389.06 g

                       = 10.389 kg

mass of ethylene glycol = 10409.88 x 1.11 = 11554.9 g

moles of ethylene glycol = 11554.9 / 62.07 = 186.16 mol

molality = moles / mass of solvent

            = 186.16 / 10.389

            = 17.92 m

delta Tf = Kb x m

   Tb - 100 = 0.512 x 17.92

Tb = 109.2

boiling point = 109.2 oC

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