Chapter: Solutions

• Introduction

  • Definition of a Solution (Homogeneous mixture of two or more components)
  • Components: Solute (minor component) and Solvent (major component)
  • Types of Solutions: Gaseous, Liquid, Solid

• Expressing Concentration of Solutions

  • Mass Percentage ($\text{w/w}$)
  • Volume Percentage ($\text{v/v}$)
  • Mass by Volume Percentage ($\text{w/v}$)
  • Parts per Million (ppm) (Trace quantities)
  • Mole Fraction ($x$)
  • Molarity ($M$) (Temperature dependent)
  • Molality ($m$) (Temperature independent)

• Solubility

  • Definition (Maximum amount of solute dissolved in a solvent at a given temperature)
  • Solubility of a Solid in a Liquid
    • Effect of Temperature (Le Chatelier's Principle: Endothermic vs Exothermic)
    • Effect of Pressure (Practically none, solids are incompressible)
  • Solubility of a Gas in a Liquid
    • Effect of Temperature (Decreases with increase in temperature)
    • Effect of Pressure and Henry's Law
      • Statement ($p = K_H \cdot x$)
      • Significance of Henry's Law Constant ($K_H$)
      • Applications (Carbonated beverages, deep-sea diving/scuba, high altitude anoxia)

• Liquid-Liquid Solutions

  • Vapour Pressure of Liquid Solutions
  • Raoult's Law
    • For volatile liquids ($p_1 = x_1 p_1^\circ$, $p_2 = x_2 p_2^\circ$)
    • Total pressure ($P_{\text{total}} = p_1 + p_2$)
  • Ideal Solutions
    • Obey Raoult's Law at all concentrations
    • $\Delta_{\text{mix}}H = 0$, $\Delta_{\text{mix}}V = 0$
    • Example: Benzene and Toluene
  • Non-Ideal Solutions
    • Do not obey Raoult's Law
    • Positive Deviation ($P > P_{\text{calculated}}$), $\Delta_{\text{mix}}H > 0$ (e.g., Ethanol + Acetone)
    • Negative Deviation ($P < P_{\text{calculated}}$), $\Delta_{\text{mix}}H < 0$ (e.g., Phenol + Aniline, $\text{CHCl}_3 + \text{CH}_3\text{COCH}_3$)
  • Azeo-tropes
    • Binary mixtures having same composition in liquid and vapour phase
    • Minimum boiling azeotropes (Large positive deviation)
    • Maximum boiling azeotropes (Large negative deviation)

• Colligative Properties

  • Definition (Properties depending only on the number of solute particles, not their nature)
  • Relative Lowering of Vapour Pressure
    • Formula: $\frac{p_1^\circ - p_1}{p_1^\circ} = x_2$
  • Elevation of Boiling Point ($\Delta T_b$)
    • Formula: $\Delta T_b = K_b \cdot m$
    • Ebullioscopic constant ($K_b$)
  • Depression of Freezing Point ($\Delta T_f$)
    • Formula: $\Delta T_f = K_f \cdot m$
    • Cryoscopic constant ($K_f$)
  • Osmotic Pressure ($\pi$)
    • Definition and Phenomenon of Osmosis
    • Formula: $\pi = CRT$ or $\pi V = nRT$
    • Isotonic, Hypotonic, and Hypertonic solutions
    • Reverse Osmosis (Water purification)

• Abnormal Molar Masses

  • Association of solute particles (e.g., Benzoic acid in benzene)
  • Dissociation of solute particles (e.g., $\text{NaCl}$, $\text{KCl}$ in water)
  • Van't Hoff Factor ($i$)
    • Formula: $i = \frac{\text{Normal molar mass}}{\text{Abnormal molar mass}} = \frac{\text{Observed colligative property}}{\text{Calculated colligative property}}$
  • Modified Colligative Equations (Multiplying by $i$)