; Chapter 14 Ions in Aqueous Solutions and Colligative Properties
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# Chapter 14 Ions in Aqueous Solutions and Colligative Properties

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```									         Chapter 14:
Ions in Aqueous Solutions and
Colligative Properties

Section 2:
Colligative Properties of Solutions
Overview

• We will examine what colligative properties
are.
• We will define the main colligative properties.
What Are They?

• Colligative Properties – Properties that
depend on the concentration of solute
particles, but not on their identity.
• Non-volatile Substance – One that has little
tendency to become a gas under existing
conditions.
Vapor-Pressure Lowering

• By adding certain
solutes the vapor
pressure of some
solvents can be
lowered.
Freezing Point Depression

• The solution also lowers the freezing point of the
solvent alone.
• Molal Freezing Point Constant – (Kf) It is for one
molal (m) of a nonvolitile, nonelectrolyte solute.
• To calculate the freezing point depression we use
the following equation:
• Δtf = Kf m
• Kf = oC/m
• m = molality
Boiling Point Elevation

• By adding solute it causes the boiling point of
the solvent to rise.
• Molal Boiling Point Constant – (Kb) It is for one
molal (m) of a nonvolitile, nonelectrolyte
solute.
• Δtb = Kb m
• Kb = oC/m
• m = molality
Osmotic Pressure

• Semipermeable Membrane – A membrane
that allows the movement of some particles
while blocking the movement of others.
• Osmosis – The movement of solvent through
a semipermeable membrane from the side of
lower solute concentration to the side of higher
solute concentration.
• Osmotic Pressure – The external pressure
that must be applied to stop osmosis.
Electrolytes
• Electrolytes tend to depress the
freezing point greatly.
• They also tend to elevate the boiling
point greatly as well.
• That is why we use salt to get rid of ice
or to prevent the formation of ice.

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