cont.

Cards (17)

  • Mass spectrometer
    Used to separate gases formed from the elements making up a complex matter
  • Precipitates
    • Large particles are more suitable for gravimetric work because they are easier to filter and give a purer product than fine particles
  • Factors that determine the particle size of precipitates
    • Colloidal dispersion
    • Crystalline suspension
  • Colloidal dispersion
    Particles visible to the naked eye (10 to 10^-6 cm in diameter), difficult to filter, show no tendency to settle from solution
  • Crystalline suspension

    Tend to settle spontaneously, easily filtered
  • Relative supersaturation
    Q/S, where Q is the concentration of the solute at any instant and S is the equilibrium solubility
  • Mechanism of precipitate formation
    1. Nucleation
    2. Particle growth
  • Colloidal precipitates
    Too small to be retained by filters
  • Peptization of colloids
    The process by which a coagulated colloid reverts to its original dispersed state
  • Crystalline precipitates are generally more easily filtered and purified than pre-coagulated colloids
  • Types of coprecipitation

    • Surface adsorption
    • Mixed crystal formation
    • Occlusion
    • Mechanical entrapment
  • Surface adsorption
    A process in which normally soluble compounds are carried out of solution by a precipitate
  • Mixed crystal formation
    One of the ions in the crystal lattice of a solid is replaced by an ion of another element
  • Occlusion
    A type of coprecipitation in which a compound is trapped within a pocket formed during rapid crystal growth
  • Mechanical entrapment
    Occurs when crystals lie close together during growth
  • Coprecipitation effects are at a minimum when the rate of precipitate formation is low, that is, under conditions of low supersaturation
  • Homogeneous precipitation
    A process in which a precipitate is formed by slow generation of a precipitating reagent