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Solutions and Colligative Properties: Rapid Review for AP Chemistry

By — McGraw-Hill Professional
Updated on Feb 2, 2011

For a more thorough review, refer to these concepts:

Rapid Review

  • A solution is a homogeneous mixture composed of a solvent and one or more solutes. A solute is a substance that dissolves in the solvent and is normally present in smaller amount.
  • The general rule of solubility is "like dissolves like." This means that polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.
  • A saturated solution is one in which the maximum amount of solute is dissolved for a given amount of solvent at a given temperature. Any solution with less than the maximum solute is called unsaturated. A solution with greater than maximum solute is supersaturated (an unstable state).
  • Solution concentration may be expressed as a percentage, which is the amount of solute dissolved per 100 units of solvent. It may be expressed as mass %, mass/volume %, or volume/volume %. Know how to calculate the appropriate percentage concentration for a solution.
  • For the chemist the most useful unit of concentration is molarity (M), which is the moles of solute per liter of solution. Know how to work molarity problems.
  • Another concentration unit is molality (m), which is the moles of solute per kilogram of solvent. Know how to work molality problems.
  • Electrolytes conduct an electrical current when melted or dissolved in a solvent, whereas nonelectrolytes do not.
  • Colligative properties are properties of solutions that depend simply on the number of solute particles and not the types. Colligative properties include:
    1. Vapor pressure lowering—The vapor pressure of the solvent is lower in a solution than in the pure solvent.
    2. Freezing-point depression—The freezing point of a solution is lower than that of the pure solvent.
    3. Boiling-point elevation—The boiling point of a solution is always higher than the boiling point of the pure solvent.
    4. Osmotic pressure—Solvent molecules pass through a semipermeable membrane from the less concentrated side to the more concentrated side. The osmotic pressure is the amount of pressure needed to stop this osmosis.
  • Know how to use the appropriate colligative properties equation to calculate the amount of vapor-pressure lowering, freezing-point lowering, van't Hoff factor, etc.
  • A colloid is a mixture in which the solute particle size is intermediate between a true solution and a suspension. If a light is shone through a colloid, the light beam is visible. This is the Tyndall effect.
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