Physical Chemistry Study Guide: Physical Properties of Solutions

Fundamentals of Solutions and the Solution Process

• Definition of Solution:

  • A solution is a homogeneous mixture composed of two or more pure substances.
  • Solutions can exist in any physical phase of matter (solid, liquid, or gas).
  • In a solution, the solute particles are dispersed uniformly throughout the solvent.

• Solute and Solvent Definitions:

  • Solute: The dissolved substance. In the case of a solution of a gas in a liquid, it is the gas. Otherwise, it is defined as the component present in the lesser amount.
  • Solvent: The dissolving medium. Generally, it is the component present in the greater amount.

• Types of Solutions with Examples:

  • Solid in Solid: Brass, which is a solid solution mixture of zinc ($Zn$) and copper ($Cu$).
  • Solid in Liquid: Sugar water, which is sucrose dissolved in water.
  • Liquid in Solid: Dental amalgam, which is mercury ($Hg$) dissolved in silver ($Ag$).
  • Liquid in Liquid: Gasoline, which is a liquid mixture of various hydrocarbons.
  • Gas in Solid: Hydrogen ($H_2$) dissolved in platinum ($Pt$).
  • Gas in Liquid: Carbonated soft drinks, which contain carbon dioxide ($CO_2$) gas dissolved in liquid water ($H_2O$).
  • Gas in Gas: Air, which is a gaseous mixture composed primarily of oxygen ($O_2$) and nitrogen ($N_2$).

• Characteristics of Liquid Solutions:

  • Liquid solutions are the most common type of solution used in chemical laboratories.
  • Many ionic compounds are soluble in water.
  • Rates of chemical reactions increase when the likelihood of molecular collisions increases.
  • This increase in molecular collisions is enhanced when molecules move freely in solution. Consequently, reactions in the liquid phase tend to occur at a more rapid rate than solid-state reactions.
  • Disadvantages of gas-phase reactions:
    • Gas particles are far apart, lowering collision frequency.
    • It is difficult or impossible to convert many compounds into the gas phase without decomposition.

• Fluid Miscibility:

  • Nonreactive gases can mix in all proportions to give a gaseous solution (e.g., air as a solution of oxygen, nitrogen, and minor gases).
  • Miscible Fluids: Liquids that dissolve in each other in all proportions.
  • Immiscible Fluids: Liquids that do not mix or dissolve in each other.

• Solid Solutions (Alloys):

  • Solid solutions of metals are referred to as alloys.
  • Brass: An alloy composed of copper ($Cu$) and zinc ($Zn$).
  • Bronze: An alloy composed of copper ($Cu$) and tin ($Sn$).
  • Pewter: An alloy composed of zinc ($Zn$) and tin ($Sn$).
  • Property alterations: Formation of an alloy can dramatically change the physical properties of the solid. For example, gold-silver ($Au/Ag$) alloys are harder and melt at lower temperatures than pure gold ($Au$).

• **The Principles of Solubility (