Physical Chemistry

• A solution is a homogeneous mixture of 2 or more substances in the same or different physical phases
• In a binary solution, the solvent is the component present in large quantities, while the other component is known as the solute
• Homogeneous solutions have the same composition and properties throughout, like a solution of NaCl or sugar in water
• Heterogeneous solutions do not have the same composition and properties throughout, like a solution of oil and water
• Solutions can be classified based on the types of solute and solvent present
• Expressing concentration of solutions involves methods like mass percentage, volume percentage, mass by volume percentage, parts per million, mole fraction, molarity, molality, normality, and formality
• Solubility is a physical property of a solution determined by factors like the nature of solute and solvent, molecular size of solute, polarity, temperature, and pressure
• Solubility of a solid in a liquid depends on the polarities of the solute and solvent, with polar solutes dissolving in polar solvents and nonpolar solutes in nonpolar solvents
• Important concepts related to solubility include dissolution, crystallization, equilibrium, and saturated solutions
• Le Chatelier's Principle states that the solubility of a substance in a solution can be affected by temperature changes
• Pressure does not significantly affect the solubility of solids in liquids due to their incompressibility
• Solubility of a gas in a liquid is exemplified by aerated drinks and dissolved oxygen in water bodies
• The phenomenon of an increase in the concentration of a solution due to the dissolving of a solid solute into the solvent is called dissolution
• Crystallisation is the process of collision of solute particles in a solution resulting in the separation of the solute particles from the solution
• An example of crystallisation is the formation of copper sulphate crystals obtained by the crystallisation of a Copper Sulphate solution
• Equilibrium is a phase where the number of solute particles entering the solution equals the number of solute particles separating from the solution
• The solubility of a gas in a liquid is influenced by temperature and pressure
• An increase in temperature decreases the solubility of gases in liquids due to dissolution being an exothermic process, similar to condensation, leading to a decrease in solubility
• Increasing pressure by compressing the gas increases the solubility of gases in liquids by increasing the number of gaseous particles per unit volume above the solution
• Henry's Law establishes a quantitative relation between pressure and solubility of a gas in a solvent, stating that the solubility of a gas in a liquid is directly proportional to the pressure of the gas at a fixed temperature
• Henry's Law equation: p = KH x, where KH is the Henry Law constant
• Different gases have different Henry Law constants (KH) at a constant temperature, with increasing KH implying lower solubility of the gas in the liquid
• Henry's Law has various applications, such as in sealing soft drink bottles at high pressure to increase the solubility of CO2 in soft drinks
• Raoult's Law establishes a quantitative relationship between the partial vapour pressure and the mole fraction of a solution, specifically for liquid-liquid solutions
• Raoult's Law is a specific case of Henry's Law, where the partial vapour pressure of each component in the solution is directly proportional to its mole fraction
• Ideal solutions follow Raoult's rule over the entire range of temperature and concentration, with properties like ΔmixH = 0 and ΔmixV = 0
• Non-ideal solutions deviate from Raoult's Law over a broad concentration range, showing characteristics like ΔmixH ≠ 0 and ΔmixV ≠ 0
• Non-ideal solutions are categorized into positive deviation and negative deviation from Raoult's Law
• Positive deviation from Raoult's Law occurs when the component's vapour pressure is higher than expected, with weaker solute-solvent forces of attraction
• Examples of positive deviation include Acetone and Carbon disulphide, Acetone and Benzene, Carbon Tetrachloride and Toluene or Chloroform, Ethanol and Water, Acetone and Ethanol, Methyl alcohol and
• Positive Deviation from Raoult’s Law:

  • Examples include: Acetone and Carbon disulphide, Acetone and Benzene, Carbon Tetrachloride and Toluene or Chloroform, Ethanol and Water, Acetone and Ethanol, Methyl alcohol and Water
• Negative Deviation from Raoult’s Law:

  • Occurs when the total vapour pressure is less than what it should be according to Raoult’s Law
  • Happens when PA < PA0 xA and PB < P0B xB
  • Solute-solvent interaction is more vital than solute-solute and solvent-solvent interaction
  • Enthalpy of mixing is negative (Δmix H < 0)
  • Volume of mixing is negative (Δmix V < 0)
  • Examples include: Acetone and Aniline, Chloroform and Benzene, Chloroform and Diether, Nitric Acid (HNO3) and water, Acetic Acid and pyridine, Hydrochloric Acid (HCl) and Water
• Azeotropes:

  • Binary mixes that boil at the same temperature and have the same composition in the liquid and vapour phases
  • Minimum Boiling Azeotrope: Formed by solutions with a considerable positive departure from Raoult’s Law
  • Maximum Boiling Azeotrope: Formed by solutions with a substantial negative divergence from Raoult’s Law
• Colligative properties:

  • Depend on the number of solute particles in a solution
  • Include: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmosis and osmotic pressures
• Relative Lowering of Vapour Pressure:

  • Non-volatile solute mixed with a solvent lowers the vapour pressure
  • Raoult’s Law: Partial vapour pressure of each component in the solution is directly proportional to its mole fraction
  • Formula for determining total molar mass of a solute: Psolvent = Xsolvent Posolvent
• Elevation of Boiling Point:

  • Vapour pressure increases when a non-volatile solute is added with a solvent
  • Boiling point of the solution is higher than the pure solvent
  • Formula: ΔT = iKbm
• Depression of Freezing Point:

  • Vapour pressure decrease leads to a lower freezing point
  • Freezing point is directly proportional to the molality of the solute
  • Formula: ΔT = iKfm
• Osmosis and Osmotic Pressure:

  • Osmosis: Flow of solvent molecules from pure solvent to solution through a semipermeable membrane
  • Osmotic Pressure: Excess pressure applied to prevent osmosis
  • Osmotic pressure depends on the concentration of the solution
  • Formula: π=CRT
• Abnormal Molar Masses:

  • Occur when molar mass differs from the theoretically expected value
  • Van’t Hoff factor accounts for the degree of dissociation or association
  • Formula: i = Normal molar mass / Abnormal molar mass
• Important Relationships:

  • Dilution Law: M1V1 = M2V2 & N1V1 = N2V2
  • Molarity and Normality: Normality = Z x Molarity
  • Solubility: Maximum amount of solute that can be dissolved in a given amount of solvent