Factors Affecting Solubility

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Factors Affecting Solubility
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Molecular Structure

• Like dissolves like
• Polar substances dissolve well in polar solvents
• Non-polar substances dissolve well in non-polar
  solvents
• Has to do with the heats absorbed or released in
  the dissolving process

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• ?H1 ?H2 ?H3
  ?Hsoln Outcome
• --------------------------------------------
  -----------------
• Polar Solute,
• Polar Solvent
• Polar Solute,
• Non-Polar solv
• Non-polar solute,
• Non-Polar solv
• Non-polar solute,
• Polar Solvent

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Pressure

• Has little or no effect on the solubilities of
  liquids or solids
• Has a great effect on the solubility of gases
• Higher the pressure, the greater the solubility
  of a gas

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Henrys Law

• The amount of gas dissolved in a solution is
  directly proportional to the pressure of the gas
  above the solution
• P kC
• P- partial pressure of the gas
• k constant of the solution
• C concentration of the solution

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Example

• A soft drink is bottled so that a bottle at 25C
  contains carbon dioxide gas at a pressure of
  5.0atm over the liquid. The Henrys law constant
  for carbon dioxide in solution is 32 L atm/mol.
  Calculate the concentration of carbon dioxide in
  the soda.

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Temperature

• For most solids and liquids, solubility increases
  with increasing temperature
• For some though, solubility decreases as temp
  increases
• There is no way to really predict how solubility
  of liquids and solids will change with temp.
• Experimental results are the only thing reliable

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Example

• From solubility graph on page 525, tell
  solubility of
• a) sugar at 50C
• b) cerium sulfate at 20C
• c) potassium nitrate at 80C

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Temp and Gases

• Solubility of gases decreases with increasing
  temperature
• What is thermal pollution?