Chemistry: Solutions and Their Properties

Concentration

• Measures the amount of solute dissolved in a given amount of solvent
• Expressed in terms of:
  • Molarity (M): moles of solute per liter of solution (mol/L)
  • Molality (m): moles of solute per kilogram of solvent (mol/kg)
  • Mass percentage: mass of solute per 100 grams of solution
  • Volume percentage: volume of solute per 100 mL of solution

Boiling Point Elevation

• The boiling point of a solution is higher than that of the pure solvent
• The amount of boiling point elevation depends on:
  • The concentration of the solution
  • The molecular weight of the solute
  • The boiling point of the pure solvent
• Boiling point elevation (ΔTb) is directly proportional to the molality of the solution

Osmosis

• The movement of solvent molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane
• Types of osmosis:
  • Isotonic: equal concentration of solute on both sides of the membrane
  • Hypotonic: lower concentration of solute on one side of the membrane
  • Hypertonic: higher concentration of solute on one side of the membrane

Freezing Point Depression

• The freezing point of a solution is lower than that of the pure solvent
• The amount of freezing point depression depends on:
  • The concentration of the solution
  • The molecular weight of the solute
  • The freezing point of the pure solvent
• Freezing point depression (ΔTf) is directly proportional to the molality of the solution

Molarity and Molality

• Molarity (M): moles of solute per liter of solution (mol/L)
• Molality (m): moles of solute per kilogram of solvent (mol/kg)
• Molarity and molality are related by the density of the solution

Heat Curves

• A graph of the temperature of a solution versus time as it freezes or boils
• Heat curves can be used to:
  • Determine the freezing point of a solution
  • Determine the boiling point of a solution
  • Identify the melting point of a pure substance

Solubility

• The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature
• Factors affecting solubility:
  • Temperature: solubility often increases with increasing temperature
  • Pressure: solubility often increases with increasing pressure
  • Polarity: solutes dissolve in solvents with similar polarity