solubility phenomena

• What is a solution?

  Mixture forming a single homogeneous phase
• What is solubility?

  Maximum concentration of a substance in solvent
• What is dissolution?

  Process of a solid entering solution
• What are the types of pharmaceutical solutions?

  • Solid-in-liquid systems
  • Gas-in-liquid systems
  • Liquid-in-liquid systems
  • Gas-in-gas systems
  • Solid-in-solid systems
• What is a solute?

  Dissolved agent in a solution
• What is a solvent?

  Component in which solute is dissolved
• What happens when a solid is brought into contact with a liquid?

  Molecules leave solid until equilibrium is established
• What is a saturated solution?

  Solution at equilibrium between undissolved and dissolved solute
• How is solubility measured in the laboratory?

  Using excess solid drug in known solvent
• What is the key point about expressing concentration?

  Concentration is expressed using weight in solvent
• What does the equation $\Delta G =$$\Delta H - T \Delta S$ represent?


  Change in free energy for dissolution
• What must $\Delta G$ be for dissolution to occur spontaneously?


  $\Delta G$ must be negative
• What are the two driving forces for any reaction according to thermodynamics?

  Disorder and attractive forces
• What happens to solubility with every 100°C increase in melting point above 25°C?

  Results in a 10-fold decrease in solubility
• What is endothermic dissolution?

  Heat is absorbed during dissolution
• What is exothermic dissolution?

  Heat is evolved during dissolution
• How does temperature affect solubility in endothermic dissolution?

  Higher temperature increases solubility
• How does temperature affect solubility in exothermic dissolution?

  Higher temperature decreases solubility
• What is a saturated solution?

  Equilibrium between undissolved and dissolved solute
• What is an unsaturated solution?

  Concentration of solute is less than saturation
• What is a supersaturated solution?

  Contains more dissolved solute than normal
• What is a hydrophilic substance?

  A polar substance that bonds with water
• What is a hydrophobic substance?

  A non-polar substance that does not bond with water
• How are solvents classified based on interaction forces?

  1. Polar solvents: strong dipolar molecules
  2. Semipolar solvents: strong dipolar without hydrogen bonds
  3. Non-polar solvents: small or no dipolar character
• What are the categories of drugs based on formal charge?

  • Anionic
  • Cationic
  • Amphoteric
  • Non-ionic
• What is ionisation in the context of drugs?

  Process producing a formal charge on a molecule
• What percentage of drugs are weak electrolytes?

  75% of drugs
• What are strong electrolytes?

  Substances that undergo complete dissociation
• What are weak electrolytes?

  Substances that only partially dissociate
• What are non-electrolytes?

  Non-ionic substances without dissociable ions
• How do multiple solutes affect solubility?

  • Electrolytes increase solubility of other electrolytes
  • Non-electrolytes decrease solubility of electrolytes
  • Very soluble electrolytes reduce solubility of non-electrolytes
• What is salting out?

  Precipitation of organic solutes by adding salt
• What is salting in?

  Increase in solubility upon adding an electrolyte
• What is partial miscibility?

  Ability to form a homogeneous dispersion in some proportions
• What is complete miscibility?

  Ability to form a homogeneous dispersion in any proportion
• What is immiscibility?

  Inability to form a homogeneous dispersion
• What molecular characteristics affect solubility?

  • Chemical composition dictates solubility
  • Hydrophilic groups impart water solubility
  • Hydrophobic groups impart oil solubility
  • Ionised species have high aqueous solubility
• What is the solubility of benzene?

  1.8 g/100 mL
• What is the solubility of anilinium chloride?

  107 g/100 mL
• What is the solubility of codeine?

  0.8 g/100 mL