AP Chemistry/Solutions

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Molarity versus Molality

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  • Molarity (M) - moles of solute per liter of solution.
  • Molality (m) - moles of solute per kilogram of solvent.

Solubility Rules

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These will NOT be given to you on the test. You must memorize them.

  1. Compounds with Group 1 elements are soluble or the ammonium ion are soluble.
  2. Nitrates, acetates, chlorates, and perchlorates are soluble.
  3. Chlorides, bromides, and iodides are generally soluble, unless they contain copper, silver, lead, or mercury.
  4. Sulfates are soluble, unless they contain barium, lead, silver, strontium, or calcium.
  5. Most silver salts are insoluble unless listed in rule #2.
  6. Most hydroxide salts are insoluble unless stated in rule #1 or contain calcium, strontium, or barium.
  7. Most sulfides are insoluble unless stated in rule #1, or contain Group 2 elements.
  8. Carbonates and phosphates are insoluble unless listed in rule #1.

Forgot Your Polyatomic Ions?

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  • Ammonium -
  • Nitrate -
  • Acetate -
  • Chlorate -
  • Perchlorate -
  • Sulfate -
  • Carbonate -
  • Phosphate -


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  • Solids are more soluble when they are warm, but gases are the opposite.
  • Supersaturated solutions will settle if disturbed.

Colligative Properties

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Colligative properties are properties of solutions that depend on the amount of solute particles present rather than the identity of the particles.

  • Vapor pressure lowering
  • Freezing point depression and boiling point elevation (molality)
  • Osmotic pressure

Not Solutions

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  • Colloids look "milky" when light is passed through them (Tyndall Effect)
  • Suspensions settle if left long enough, and also look milky.