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Understanding Solutions and Their Properties

May 5, 2025

Solutions and Solubility Lecture Notes

Solutions

  • Solution: A homogeneous mixture where a solute is dissolved in a solvent.
    • Can be colored or colorless; must be transparent.
  • Aqueous: A solution where water is the solvent.
  • Solute: The substance dissolved in a solution (e.g., sugar).
  • Solvent: The substance that dissolves the solute (e.g., water).

Water as a Solvent

  • Known as the universal solvent due to its ability to dissolve many solutes.
    • Reasons:
      1. Abundance and availability.
      2. Polar nature with slight positive and negative ends.

Dissolving Processes

  1. Ionic Dissociation
    • Ionic compounds separate into ions when dissolved.
    • Water molecules surround ions, preventing them from attracting each other.
    • Example: Sodium chloride dissociates into sodium cations and chloride anions.
    • Hydration: Process where ions are surrounded by water.
  2. Molecular Dissociation
    • Separation of molecular solutes by a solvent into different phases.
  3. Covalent Ionization
    • Chemical process, occurring with acids and ammonia, where molecules react to produce ions.

Rate of Dissolving and Solubility

  • Rate of Dissolving: Speed at which a solute dissolves in a solvent.
    • Influenced by temperature, agitation, and particle size.
    • Increased temperature, agitation, and surface area lead to faster dissolving.
  • Solubility: Maximum amount of solute that can dissolve at a constant temperature.
    • "Like dissolves like": Polar solutes dissolve in polar solvents and non-polar in non-polar.

Effects of Temperature and Pressure on Solubility

  • Temperature:
    • Solids: Solubility increases with temperature.
    • Liquids: Solubility unaffected.
    • Gases: Solubility decreases with temperature.
  • Pressure: Affects only gases; increased pressure increases the solubility of gases in liquids.

Types of Solutions

  • Saturated: No more solute can dissolve at a certain temperature.
  • Unsaturated: More solute can dissolve.
  • Supersaturated: Contains more dissolved solute than normally possible; unstable.

Hydrogen Bonding and Water

  • Significance: High melting/boiling points, ice floats, high surface tension, thermal energy exchange.
  • Intermolecular Forces: Dipole-dipole, ion-dipole, and hydrogen bonding (strongest intermolecular bond).

Concentration Measures

  • Molar Concentration (Molarity): Moles of solute per liter of solution.
  • Dilutions
    • Process of reducing concentration by adding more solvent.
    • Stock solutions as starting point for dilutions: C1V1 = C2V2.
  • Percent Concentrations
    1. Mass/Volume percent (m/v%): Mass of solute per volume of solution.
    2. Mass/Mass percent (m/m%): Mass of solute per mass of solution.
    3. Volume/Volume percent (v/v%): Volume of solute per volume of solution.
    4. Parts per million (ppm), billion (ppb), trillion (ppt): Mass of solute per mass of solution.

Solubility Rules and Precipitation

  • Solubility: Maximum solute dissolvable in a solvent.
  • Insoluble: Less than 0.1g solute dissolves in 100mL solvent.
  • Slightly Soluble: Between 0.1g and 1.0g per 100mL.
  • Precipitate: Insoluble product from reaction of aqueous substances.
  • Solubility Rules: Help predict precipitation in double displacement reactions.
    • Net Ionic Equations: Include only ions participating in the reaction; spectator ions are omitted.