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 5.30 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. Also, you\'ll need to look up the boiling-point elevation constant for water.

Answer 1

Boiling point elevation

dT = i * Kb * m

van't Hoff factor for ethylene glycol i = 1

Kb = boiling point elevation constant for water = 0.512 °C/m

m = molality = moles of solute/kilogram of solvent

Volume of solution = 5.30 gallons x 3.785 L/gallon

= 20.0605 L

Volume of ethylene glycol = 0.5*20.0605 = 10.03 L

Mass of ethylene glycol = volume x density

= 10.03 L x 1000 mL/L x 1.11 g/mL

= 11133.57 g

Moles of ethylene glycol = mass/molecular weight

= 11133.57 g / 62.07 g/mol

= 179.37 mol

Mass of water = 10.03 L x 1000 mL/L x 0.998 g/mL

= 10009.94 g x 1kg/1000g

= 10 kg

Molality = 179.37 mol/10 kg

= 17.937 m

dT = 1 x 0.512 x 17.937

= 9.174 °C

Boiling point of solution = 100 + 9.174 = 109.174 °C