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

Question

18) 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 5.10 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 (HOCH2CH2OH), which is non-ionizing and non-volatile, and that the pressure remains constant at 1.00 atm.

Explanation / Answer

to calculate the new boiling point of a solution: Tb-Tbº = (kb)(m)

m= mass/(molecular weight solute)(kg of solvent).

throught the densities, masses instead of volumes can be obtained: m=(d)(V). Consider 1gallon = 3.785L

mH2O= (0.998g/ml)(9651.75ml) = 9632.4465g = 9.6324kg of Water

mE.G= (1.11g/ml)(9651.75ml)=10713.4425g of ethylene glycol. (molecular weight = 62.06784g/mol)

Then the molality of the solution is: m= 10713.4425g / (62.06784g/mol(9.6324kg)) =17.9196m

And now using the equation for the difference of boiling point, and knowing kb for water is 0.52ºC/m:

T-100ºC= 0.52ºC/m(17.9196m).... T= 109.32ºC

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