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

Question

A 50/50 Wend of engine coolant and water (by volume) is usually used in an automobile's engine cooling system. If your car's cooling system holds 4.80 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

As you may already know, boiling point elevation is colligative property which is equal to DT = i * Kb * m

i = van't Hoff factor = 1

Kb = boiling point elevation constant of water = 0.512

m = the molality (moles of solute per kilogram of solvent)

4.8 gallon = 18.7 L, hence ethylene glycol is 18.7/2 = 9.35 L

With a density of 1.11g/mL we can compute that there are 10,378.5 grams of the solute. Knowing the molar mass of ethylene glycol, 62.07 g mol1, we find that there are 167.2 moles.

9.35 L of water has a mass of 9.33 kilograms using the density of water.

The molaity is therefore 167.2 moles / 9.33 kilograms = 17.92 mol / kg

The temperature increase is DT = 1 * 0.512 * 17.92 = 9.175 C
This gives us a boiling point of 109.175C

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