Molarity and Colligative
Properties
Video Notes
Molarity and Colligative Properties
• Calculate molarity of a solution.
• Learn how to prepare specific solution
concentrations.
• Identify colligative properties and explain
their significance to everyday life.
Molarity and Colligative Properties
• Molarity
Expresses solution concentration
M = moles of solute
liters of solution
o Molarity, molar, M and mol / liter all represent the
same ratio
o
o
Molarity and Colligative Properties
• M = moles of solute
liters of solution
• 1 M NaCl = 1 mole NaCl
1 liter of solution
• ? g = 1 mol NaCl
• 23.0g Na, 25.5 Cl
• = 58.5 g NaCl
Molarity and Colligative Properties
• Saline solution contains 0.90g of NaCL per
95 mL of solution
• ? Mole
• 0.90 g NaCl x 1.0 mol NaCl = 0.015 mol
58.5 g NaCl
• 95 mL = 0.095L
• 0.015 mol/ 0.095L = 0.16 M
Molarity and Colligative Properties
• How many moles of solute are contained in
2.5L of 0.30 M CaCl2
• 0.30 M CaCl2 = moles of solute / 2.5 L
• 0.75 mol
• Mass of solute is 83g CaCl2
Molarity and Colligative Properties
• Colligative Properties
Any of the properties of a solution that change
when the concentration of the solution changes.
o Depend on the number of particles dissolved in a
given mass of solvent.
o
Molarity and Colligative Properties
• Examples of Colligative Properties
o
Vapor Pressure Depression
 Lowering of the vapor pressure of a liquid that occurs
when substances are dissolved in the liquid.
 Vapor pressure is the pressure of a vapor that is in
equilibrium with its liquid
 When measured, tends to be mixed with water vapor.
Molarity and Colligative Properties
• Examples of Colligative Properties
o
Freezing point depression
 The lowering of the freezing point of a liquid that
occurs when substances are dissolved in the liquid.
 Antifreeze – solution mixed into water to lower
freezing point.
 Using salt on sidewalk – salt melts ice and prevents
ice from refreezing.
 Using rock salt with ice cream mixer.
Molarity and Colligative Properties
• Examples of Colligative Properties
o
Boiling point elevation
 Raising of the boiling point of a liquid that occurs
when substances are dissolved into the liquid.
 Boiling occurs when vapor pressure equals external
pressure.
 Antifreeze prevents coolant from boiling at boiling
point of water.