Chemistry Notes: Solutions and Mixtures

Heterogeneous and Homogeneous Mixtures

  • Mixtures: Combinations of two or more substances where individual properties are retained.
  • Mixtures can be separated physically and have variable proportions.
  • Two categories:
    • Homogeneous Mixtures:
    • Uniform composition throughout.
    • No visible boundaries.
    • Components are evenly distributed (e.g., sugar in water).
    • Example: Solutions, where the major component is the solvent and minor component is the solute.
    • Heterogeneous Mixtures:
    • Non-uniform composition with visibly distinct parts (e.g., oil and water).
    • Examples: Sand + water, salad, and pizza.

Classifying Mixtures

  • Activity: Classify mixtures as homogeneous or heterogeneous:
    • Sand + water: Heterogeneous
    • Coffee: Homogeneous
    • Sea water: Homogeneous
    • Air: Homogeneous
    • Brass: Homogeneous (Alloy)
    • Steel: Homogeneous (Alloy)
    • Natural gas: Homogeneous
    • Pizza: Heterogeneous
    • Vinegar: Homogeneous
    • Vegetable salad: Heterogeneous
    • Fruit punch: Homogeneous
    • Blood: Heterogeneous
    • Milk: Colloidal mixture (can be classified as heterogeneous)
    • Butter: Homogeneous
    • Clouds: Colloidal mixture (can be classified as heterogeneous)

Suspensions, Solutions, and Colloids

  • Suspensions:
    • Heterogeneous mixtures where solid particles are dispersed in a liquid but do not dissolve (e.g., muddy water).
  • Solutions:
    • Homogeneous mixtures consisting of a solute dissolved in a solvent (e.g., sugar in water).
    • Particle sizes are atomic/molecular.
    • Components remain mixed and do not settle out.
    • Example: Saltwater
    • Types of Solutions:
    • Gaseous Solutions: Mixtures of gases (e.g., air).
    • Liquid Solutions: Mixtures of solids, liquids, and gases in liquid solvent (e.g., beverages).
    • Solid Solutions: Alloys and some solid mixtures (e.g., dental filling).

Properties of Solutions

  • Characteristics:
    • Single phase with no visible boundaries.
    • Cannot be separated by filtration.
    • Stable over time, components do not separate or settle.

Colloids:

  • Heterogeneous mixtures that exhibit properties between suspensions and solutions.
  • Particles range from 1 nm to 100 nm and cannot be separated by filtration.
  • Example: Milk and fog.
  • Tyndall Effect: Scattering of light by colloidal particles making the path of light visible in the mixture (observed in colloids but not in true solutions).

Types of Colloids

  • Based on Dispersed Phase and Medium:
    • Aerosol: Liquid in gas (e.g., fog).
    • Foam: Gas in liquid (e.g., shaving cream).
    • Emulsion: Liquid in liquid (e.g., milk).
    • Sol: Solid in liquid (e.g., muddy water).
    • Gel: Liquid in solid (e.g., jelly).
    • Solid Sol: Solid in solid (e.g., colored gemstones).

Processes in Mixtures

  • Coagulation:
    • The process where stable colloidal dispersions aggregate and separate from the continuous phase (e.g., curdling milk).
  • Association Colloids:
    • Colloids formed by the association of surfactants into micelles. (e.g., soap in water.)

Interactions and Dissolution

  • Dissolution Process:
    1. Breaking solute-solute interactions.
    2. Breaking solvent-solvent interactions.
    3. Forming solute-solvent interactions.
  • The process can be influenced by temperature, surface area, and solute-solvent interaction strength.
  • Energy Changes:
    • Can be exothermic (releases heat) or endothermic (absorbs heat).
    • ΔHsoln determines how the solution behaves energetically.

Concentration Measures:

  • Percent by Mass:
    • Example Calculation: % = (mass of solute/(mass of solution)) * 100
  • Molarity (M):
    • M = moles of solute / volume of solution in L
  • Molality (m):
    • m = moles of solute / mass of solvent in kg
  • Normality (N):
    • N = equivalents of solute / volume of solution in L

Review of Key Terms

  • Concentration, solubility, saturated and unsaturated solutions, properties of mixtures and solutions, types of mixtures, types of colloids, energy changes during dissolution
  • Important to focus on practical applications (like the importance of solutions in daily life: cooking, cleaning, medicine, etc.).