Chemistry (Chang), 9th Edition

Chapter 12: Physical Properties of Solutions

Chapter Summary

1. Solutions are homogeneous mixtures of two or more substances, which may be solids, liquids, or gases.

2. The ease of dissolving a solute in a solvent is governed by intermolecular forces. Energy and the disorder that results when molecules of the solute and solvent mix to form a solution are the forces driving the solution process.

3. The concentration of a solution can be expressed as percent by mass, mole fraction, molarity, and molality. The choice of units depends on the circumstances.

4. Increasing temperature usually increases the solubility of solid and liquid substances and usually decreases the solubility of gases in water.

5. According to Henry’s law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas over the solution.

6. Raoult’s law states that the partial pressure of a substance A over a solution is equal to the mole fraction (X_A) of A times the vapor pressure (P^°_A) of pure A. An ideal solution obeys Raoult’s law over the entire range of concentration. In practice, very few solutions exhibit ideal behavior.

7. Vapor-pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure are colligative properties of solutions; that is, they depend only on the number of solute particles that are present and not on their nature.

8. In electrolyte solutions, the interaction between ions leads to the formation of ion pairs. The van’t Hoff factor provides a measure of the extent of dissociation of electrolytes in solution.

9. A colloid is a dispersion of particles (about 1 × 10³ pm to 1 × 10⁶ pm) of one substance in another substance. A colloid is distinguished from a regular solution by the Tyndall effect, which is the scattering of visible light by colloidal particles. Colloids in water are classified as hydrophilic colloids and hydrophobic colloids.