Problem of the Week

Chapter 13: Water and Its Solutions

Problem of the Week

Teachers Notes:

Ice cream experiments:
Ice Cream
We All Scream for Ice Cream
Coffee Can Ice Cream
Plastic Bag Ice Cream

Problem 1:
Emulsions are created by dispersing one liquid in another liquid by applying mechanical energy to disrupt one of the phases into small droplets. An emulsion in a colloidal system which is defined as having one or more components with a size ranging from 1nm to 1000nm in diameter.

Problem 2:
Total mass of solution = 1200.0 g NaCl + 7300.0 g H²O = 8500.0g

Total volume of solution = 8500.0 g NaCl solution x (1 mL/1.089 g NaCl solution) = 7805 mL or 7.805 L

Molarity = 1200.0 g NaCl x (1 mol NaCl/58.5 g NaCl) x (1/7.805 L) = 2.63 mol/L NaCl or 2.63 M NaCl

Molality = 1200.0 g NaCl x (1 mol NaCl/58.5 g NaCl) x (1 / 7.3000 kg) = 2.80 mol NaCl/kg or 2.80 m NaCl

Mass percent = 1200.0 g NaCl x (1/8500.0 g solution) x 100 = 14.118 % NaCl

Mole fraction NaCl
Mol NaCl = 1200.0 g NaCl x (1 mol NaCl/58.5 g NaCl) = 20.5 mol NaCl
Mol H₂O = 7300.0 g H₂O x (1 mol H₂O/18.0 g H₂O) = 406 mol H₂O
Total mol = 20.5 NaCl + 406 mol H₂O = 426.5 mol solution

Mol fraction NaCl = 20.5 mol NaCl / 426.5 mol solution = 0.0481 mol fraction NaCl

Problem 3:
Molality of NaCl = 20.0 g NaCl x (1 mol NaCl/58.5 g NaCl ) x (1/ 0.080 kg H₂O) = 4.27 m NaCl

Particle molality = 2 mol ions/mol NaCl x 4.27 m NaCl = 8.54 m
Freezing point depression
ΔΤ= 8.54 m x (1.86 C°/molal) = 15.9 C°
New freezing point = 0.0C° - 15.9C° = -15.9 C°