Chapter 10

1
Chapter 10 Solutions Their Properties

• Molarity (M)
• Moles of solute (mol) per liters (L) of solution
• Dilution Formula
• Used when preparing diluted solutions from
  concentrated ones.
• Mole Fraction
• Used previously for gas problems.
• XA moles A nA
• total moles ntot
• Mole fraction of a component of the solution will
  equal moles of that component divided by the
  total moles present. The sum of the mole
  fractions should equal 1.

2
Mass Percent ()

• Mass percent is determined by the mass of the
  solute divided by the total mass of the solution,
  then multiplied by 100.
• Example If a solution is prepared by dissolving
  24 g of NaCl in 152 g of water, calculate the
  percent, by mass, of NaCl.
• Sometimes when the amounts are so small (trace
  amounts) we use parts per million (ppm) or parts
  per billion (ppb). For example, if we have 5 x
  10-8 grams of arsenic in 1.00 grams of water that
  will be equivalent to 0.05 ppm of Arsenic in
  water.
• For ppm we multiply by a factor of 106 and for
  ppb we multiply by a factor of 109.

3
Molality (m)

• Molality is determined my moles of solute per
  kilograms of solvent.
• m moles of solute
• kilograms of solvent
• Conversions between concentration units
• Please reference example 10.4 on page 261.

4
Principles of Solubility

• Like dissolves like..meaning polar generally
  dissolves polar and nonpolar dissolves nonpolar.
• Effects of Temperature
• Solids the higher the temperature, generally
  the higher the solubility. An increase in
  temperature always shifts the position of an
  equilibrium to favor an endothermic process,
  which means H gt0.
• Gases become less soluble as the temperature
  rises. Why?
• Effects of Pressure
• Pressure only has an effect on gas-liquid
  solutions. Do pressure and the solubility of a
  gas have an inverse or direct relationship?
• Henrys Law
• Cg kPg
• Cg concentration of the gas (M)
• k constant for the gas-liquid system this
  will vary (M/atm)
• Pg Pressure of the gas (atm)
• Example 10.5 Page 264

5
Colligative Properties of Nonelectrolytes

• Properties of solutions differ from the
  properties of the pure solvent.
• The solution properties depend more so on the
  concentration of the solute particles.
• Vapor Pressure Lowering
• Boiling Point Elevation
• Freezing Point Lowering

6
Vapor Pressure Lowering

• Concentrated solutions evaporate more slowly
  than pure water, meaning they have a lower vapor
  pressure.
• With an increase in concentration of solute the
  vapor pressure lowers this is Raoults Law
• ?P X2 P10
• ?P change in pressure (P10 - P1) - mmHg
• X2 mole fraction of solute
• P10 vapor pressure of the pure solvent - mmHg
• Example 10.6 page 265

7
Boling Point Elevation

• A solution does not begin to boil until the
  temperature exceeds that of the solvent. The
  greater the concentration of the solute the
  higher the temperature needed to boil the
  solution
• ?Tb kb x m
• m molality (m)
• kb Molal Boiling Point Constant (0C/m)
• ?Tb change in temp at which solution boils (Tb
  - Tb0)
• -Tb the temp at which the solution boils
• -Tb0 the temp at which the pure solvent boils
• Example 10.7 page 167

8
Freezing Point Depression

• When a solution is cooled it does not begin to
  freeze until a temperature below the freezing
  point of the solvent is reached. The greater the
  concentration the lower the temperature required
  for freezing
• ?Tf kf x m
• m molality
• kf Molal freezing point constant
• ?Tf change in temp at which solution freezes
  (Tf0 - Tf)
• Tf the temp at which the solution freezes
• Tf0 the temp at which the pure solvent freezes

9
Osmotic Pressure

• Osmosis is a process taking place through a
  membrane permeable to only the solvent is called
  osmosis. Water moves from a region where its
  vapor pressure or mole fraction is high to one in
  which its vapor pressure or mole fraction is
  low.
• Osmotic pressure is directly proportional to the
  molarity (M) this is why it is a colligative
  property
• p nRT MRT
• V
• Example 10.8 page 269