Question

1.) An automobile mechanic mixes ethylene glycol with water to make a solution of automobile antifreeze.

This mixture contains 1104g of ethylene glycol and 1.50 kg of pure water. What is the freezing point of this solution in degrees Celsius? (Assume 1 atm pressure).

2.) A zoologist combines NaCl with pure water for use in an outdoor aquatic facility. She makes the salt/water mixture by dissolving 15.0 kg of NaCl and 400.0 kg of pure water. What is the freezing point of this solution in degrees Celsius? (Assume 1 atm pressure).

Answer 1

m = 1104 g of et glyc

m = 1.5 kg water

Kf = -1.86 for water

Tf = -KF*m

MW et glyc = 62.07 g7mol

mol = mass/MW = 1104/62.07 = 17.78637 mol

m = mol/kg = 17.78637/1.5 = 11.85758molal

then

Tf = 1.86*11.85758 = -22.0550

Tf = 0 -22.0550 = -22.0550 °|C

2)

m = 15 kg NaCl = 15000 g

mol = mass/MW = 15000/58 = 258.62068 mol NaCl

i = 2 since 2 ions will dissocaite

kg = 400 kg

m = mol/kg = 258.6/400 = 0.6465 molal

dT = -Kf*m*i

dT = -1.86*0.6465*2 = - 2.40498°C

T =0 - 2.40498 = -2.40498°C