Solubility

1
Solubility
Crystallize
Solute Solvent ? Solution
Dissolve

• Unsaturated Solution Additional solute will
  still dissolve
• Saturated Solution No additional solute will
  dissolve, equilibrium between solution and
  undissolved solute
• Supersaturated Solution Beyond the point of
  saturation

2
Salt Solubility and Health

• Sodium urate is formed from uric acid, a natural
  chemical in the body. Uric acid can also come
  from foods.
• Uric acid in normal amounts remains dissolved in
  the blood, easily passes through the kidneys and
  leaves the body as waste. Uric acid in high
  amounts, however, makes a person more likely to
  develop gout.
• Uric acid crystals deposit in the joints
• The amount of uric acid in your blood can change
  depending on
• What you eat red meats and internal organs (such
  as liver and kidneys), some shellfish and
  anchovies
• Your overall health
• How much alcohol you drink
• What medicines you are taking
• Sudden illnesses
• The kidneys' ability to rid the body of uric acid
  (heredity).

3
Solubility
Crystallize
Solute Solvent ? Solution
Dissolve

• Factors Affecting Solubility
• Energy Requirements
• Solvent-Solute interactions (like dissolves like)
• Temperature Effects
• Pressure Effects (Henrys Law)

4
The Solution Process
Energy Changes and Solution Formation
5
The Solution Process
Energy Changes and Solution Formation
CaCl2 example
NH4Cl example
6
The Solution Process

• Energy Changes and Solution Formation
• Breaking attractive intermolecular forces is
  always endothermic.
• Forming attractive intermolecular forces is
  always exothermic.
• To determine whether ?Hsoln is positive or
  negative, we consider the strengths of all
  solute-solute and solute-solvent interactions
• ?H1 and ?H2 are both positive.
• ?H3 is always negative.
• It is possible to have either ?H3 gt (?H1 ?H2)
  or ?H3 lt (?H1 ?H2).

7
The Solution Process

• Energy Changes and Solution Formation
• Rule polar solvents dissolve polar solutes.
  Non-polar solvents dissolve non-polar solutes.
  Why?
• If ?Hsoln is too endothermic a solution will not
  form.
• NaCl in gasoline the ion-dipole forces are very
  weak because gasoline is non-polar. Therefore,
  the ion-dipole forces do not compensate for the
  separation of ions (loss of ion-ion
  interactions).
• Water in octane water has strong H-bonds. There
  are no attractive forces between water and octane
  to compensate for the lost H-bonds when water
  molecules separate.

8
Salt Solubility Examples

• Some salts have very low solubility in water and
  reach saturation right away

These salts are often referred to as Insoluble
salts Ion-ion interaction are too strong to be
separated by water
9
Temperature Affects on Solubility

• Most solids increase solubility in a liquid with
  increasing temperature
• Most gases decrease solubility in a liquid with
  increasing temperature

10
Pressure Affects on Solubility

• Solubility of liquids and solids not greatly
  affected by pressure
• Solubility of gases greatly affected by pressure
  (Henrys Law)
• Increase pressure Increase solubility
• Coca-cola example

11
Gas Solubility Application
12
Bends and Scuba DivingHenrys Law in Action

• Pressure on the body increases at the divers goes
  deeper
• Increased pressure increased gas in blood
• Air is mostly nitrogen so more nitrogen than
  normal dissolved in our blood
• As the diver ascends, the gases come out
  (pressure decreases)
• Fast ascends lots of bubbles (BAD for our
  organs and joints!)

13
Altitude Illness- Mountain Sickness (Form of
Hypoxia)

• Most likely to be affected are mountain climbers,
  pilots and persons living at high altitudes above
  8,000 feet.
• High altitude low pressure low oxygen
  concentration dissolved in blood
• In a healthy person at sea level, blood is 95
  saturated with oxygen. At 18,000 feet it is only
  71 saturated.

14
Ways of Expressing Concentration

• All methods involve quantifying amount of solute
  per amount of solvent (or solution).
• Generally amounts are measures are masses, moles
  or liters.
• Qualitatively solutions are dilute or
  concentrated.
• Definitions

15
Ways of Expressing Concentration

• Parts per million (ppm) can be expressed as 1 mg
  of solute per kilogram of solution.
• Parts per billion (ppb) are 1 ?g of solute per
  kilogram of solution.
• Proof by conversion

16
Ways of Expressing Concentration
Mole Fraction, Molarity, and Molality
17
Ways of Expressing Concentration

• Mole Fraction, Molarity, and Molality
• Converting between molarity (M) and molality (m)
  requires density of solution
• L of solutions to kg of solution
• kg of solution kg solvent kg solute

moles of solute kg of solvent
molality
18
Colligative Properties

• Colligative properties depend on quantity of
  solute molecules.
• Freezing point depression
• Boiling point elevation

19

• Lowering the Vapor Pressure
• Non-volatile solvents reduce the ability of the
  surface solvent molecules to escape the liquid.
• Therefore, vapor pressure is lowered.
• The amount of vapor pressure lowering depends on
  the amount of solute.

20

• Boiling-Point Elevation
• Non-volatile solute lowers the vapor pressure.
• Higher Temperature needed to achieve 1 atm of
  vapor pressure
• Freezing-Point Depression
• Non-volatile solute lowers the vapor pressure,
  and shift triple point to lower temperature
• Lower temperature of triple point produces lower
  phase change temperature

21
Colligative Properties

• Boiling-Point Elevation
• At 1 atm (normal boiling point of pure liquid)
  there is a lower vapor pressure of the solution.
  Therefore, a higher temperature is required to
  reach a vapor pressure of 1 atm for the solution
  (?Tb).
• Molal boiling-point-elevation constant, Kb,
  expresses how much ?Tb changes with molality of
  particles, m

22
Colligative Properties

• Freezing-Point Depression
• The solution freezes at a lower temperature (?Tf)
  than the pure solvent.
• Decrease in freezing point (?Tf) is directly
  proportional to molality of particles (Kf is the
  molal freezing-point-depression constant)