Aqueous Solutions Summary

Aqueous Solutions

Solubility & Saturation

  • Solubility Definition: Amount of solute that dissolves in a specific amount of solvent (e.g., NaCl: 36 g/100 g water at 25 °C).
  • Saturated Solution: Contains maximum solute; excess solute does not dissolve.
  • Unsaturated Solution: Contains less than maximum solute; excess will dissolve.
  • Supersaturated Solution: Contains more solute than normal maximum; unstable, typically precipitates when disturbed.

Temperature Dependence of Solubility

  • General Trend: Solubility of solids in water increases with temperature.
  • Recrystallization: A method to purify solids; forms crystals as the solubility decreases when cooled.
  • Example: Rock candy production from saturated sucrose solution.

Gas Solutions in Water

  • Examples: Soda (carbon dioxide in water), lake water (dissolved oxygen).
  • Solubility Trend: Decreases with increasing temperature.
  • Pressure Influence: Higher pressure increases gas solubility (Henry’s Law).

Measures of Concentration

  • Mass Percent: g of solute per 100 g of solution. Formula: ext{Mass percent} = rac{ ext{Mass solute}}{ ext{Mass solute} + ext{Mass solvent}} imes 100 \%.
  • Molarity (M): Moles of solute per liter of solution, M = rac{ ext{Moles solute}}{ ext{Liters solution}}.
  • Conversion Factor: Mass percent and molarity are used for calculations involving solution concentrations.

Ion Concentrations

  • Concentration of ionic solutions reflects molarity before dissolution (1.0 M CaCl2 yields 1.0 M Ca²⁺ and 2.0 M Cl⁻).

Solution Dilution

  • Stock solutions are concentrated forms that are diluted using M1V1 = M2V2, where M is molarity and V is volume.
  • Important safety note: Always add acid to water, not water to acid.

Solution Stoichiometry

  • Relates volume and concentration to calculate moles for reactions.

Acid-Base Titration

  • Reacting known concentration with unknown; involves equivalence points identified by indicators (e.g., phenolphthalein).

Colligative Properties

  • Freezing Point Depression: riangle Tf = m imes Kf (varying by solute and solvent).
  • Boiling Point Elevation: riangle Tb = m imes Kb.

Osmosis & Osmotic Pressure

  • Osmosis: Solvent moves from lower to higher solute concentration.
  • Osmotic Pressure: Depends on solute concentration, affects living cells (e.g., isotonic, hypotonic, hypertonic solutions).