Unit 8 Solutions Study Guide

Types of Solutions

  • Heterogeneous Mixture: Mixture with uneven distribution of components.
  • Homogeneous Mixture: Mixture with uniform distribution.
  • Suspension: A heterogeneous mixture with large particles that settle unless stirred.
  • Colloid: A heterogeneous mixture that appears homogeneous; particles are larger than in true solution and can scatter light (Tyndall effect).
  • Solution: A homogeneous mixture of 2 or more substances uniformly dispersed.

Key Vocabulary

  • Solute: Substance that is dissolved.

  • Solvent: Substance doing the dissolving.

  • Miscible: Fluids that can mix in any proportion.

  • Immiscible: Fluids that do not mix and form separate layers.

  • Solubility: Measure of how much solute can dissolve in a solvent.

  • Electrolyte: A substance that dissociates into ions in solution and conducts electricity.

  • Strong Electrolyte: Fully dissociates in solution; good conductor.

  • Weak Electrolyte: Partially dissociates in solution; poor conductor.

  • Nonelectrolyte: Does not conduct electricity in solution.

  • Hydrates: Ionic compounds that incorporate water in crystalline forms.

Important Laws and Concepts

  • Tyndall Effect: Light scattering by colloidal particles, indicating a colloid.
  • Henry’s Law: Solubility of a gas in liquid directly proportional to the gas pressure above the liquid.

Examples of Solutions

  1. Soda: CO$_2$ (gas) in water (solution).
  2. Lemonade: Powder (solute) in water (solvent).
  3. Brass: Zinc (solute) in copper (solvent).

Differences in Mixtures

TypeHomogeneous or Heterogeneous?Particle SizeSettlingFiltrationTyndall Effect
SolutionsHomogeneousSmallestNoNoNo
ColloidsHeterogeneousIntermediateNoNoYes
SuspensionsHeterogeneousLargestYesYesSometimes

Differences in Processes

  • Dissolution: Solute separations and solvent hydration.
  • Dissociation: Separation of ions from ionic compounds in solution.

Factors Affecting Solubility

  1. Surface area: Smaller particles dissolve faster.
  2. Agitation: Stirring increases contact between solute and solvent.
  3. Temperature: Higher temperatures increase kinetic energy, enhancing solubility (for most solutes).
  4. Pressure: Primarily affects the solubility of gases.

Types of Solutions

  • Saturated Solution: Maximum solute at given conditions.
  • Unsaturated Solution: Less solute than saturation.
  • Supersaturated Solution: More solute than saturation under the same conditions.

Concentration Measures

  • Concentration: Amount of solute per amount of solvent or solution.
  • Molarity (M): Moles of solute per liter of solution.
  • Molality (m): Moles of solute per kg of solvent.

Practice: Concentration Calculations

  • Find molarity by M = mol solute / L solution.
  • Find molality by m = mol solute / kg solvent.
  • Dilution Methods: Remove solute or add solvent.

Properties of Solutions

  • Colligative Properties: Depend on solute particle concentration rather than identity.
  • Osmosis: Movement of solvent through a semipermeable membrane.
  • Freezing-point Depression: Lowering of freezing point by solute presence.
  • Boiling-point Elevation: Increase in boiling point due to solute.
  • Osmotic Pressure: Pressure applied to halt solvent movement in osmosis.

Relationships

  • More solute → Higher boiling point, Lower freezing point, Increased osmotic pressure.

  • Boiling Point of Salt Water: Higher than pure water because of solute presence, requiring more energy to change states.

  • Understanding how changes in concentration affect solution properties is key in chemistry.

Practice Calculations

  • Example problems on calculating molarity, molality, and dilutions help reinforce these concepts.