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.