Gravimetric

• What are the types of gravimetric methods?

  1. Precipitation gravimetry
  2. Electrogravimetry
  3. Volatilization gravimetry
  4. Particulate gravimetry
• How is the analyte treated in precipitation gravimetry?

  Converted to a sparingly soluble precipitate
• What is gravimetric analysis?

  Methods measuring mass or change in mass
• What happens to the precipitate in precipitation gravimetry?

  It is filtered, washed, and weighed
• What is the process in electrogravimetry?

  An analyte is deposited on an electrode
• What is the principle of volatilization gravimetry?

  Analytes are volatilized and weighed
• What is an example of volatilization gravimetry?


  Analysis of moisture in foods
• What is particulate gravimetry used for?

  Determining suspended solids in a sample
• Why is gravimetry important?

  It requires only base SI units for measurements
• What are the steps in precipitation gravimetry?

  1. Preparation of the solution
  2. Precipitation digestion
  3. Digestion
  4. Filtration
  5. Washing
  6. Drying or igniting
  7. Weighing
  8. Calculation
• What is nucleation in precipitate formation?

  Formation of stable solid from few ions
• What happens during particle growth in nucleation?

  Small particles combine to form larger ones
• What is a precipitating agent?

  Substance converting analyte into insoluble form
• What are specific reagents in gravimetry?

  Reagents that react with a single species
• What factors influence particle size of precipitate?

  Solubility, temperature, concentrations, mixing rate
• What is relative supersaturation?

  Degree of solute concentration compared to equilibrium
• What does a large relative supersaturation indicate?

  Colloidal precipitate with high nucleation rates
• What does a small relative supersaturation indicate?

  Crystalline precipitate with particle growth
• How can particle size be controlled in gravimetry?

  Use dilute solutions and slow addition of precipitant
• What is homogeneous precipitation?

  Precipitate formed by slow reagent generation
• How does temperature affect precipitate solubility?

  Higher temperatures usually increase solubility
• What are the types of precipitate?

  Gelatinous, curdy, crystalline
• What is the electric double layer?

  Composed of primary and secondary layers
• What effect does the electric double layer have?

  Exerts electrostatic repulsive force on particles
• How can coagulation be promoted?

  Avoid excess precipitant and add electrolyte
• What is digestion in gravimetry?

  Allowing precipitate to stand in its solution
• What is the purpose of filtration in gravimetry?

  Separating precipitate from the mother liquor
• What is mother liquor?

  Solution from which the precipitate forms
• What is supernatant?

  Solution remaining after removing the precipitate
• What is fritted glass?

  Finely porous glass for filtration
• What is a Gooch porcelain crucible?

  Crucible with a perforated base for filtration
• How can peptization be avoided?

  Use dilute electrolyte instead of water
• What are the types of coprecipitation?

  1. Mixed crystal formation (Inclusion)
  2. Occlusion
• What is mixed crystal formation in coprecipitation?

  Contaminant replaces an ion in crystal lattice
• What is occlusion in coprecipitation?

  Foreign ion trapped during rapid crystal growth
• How can inclusion be minimized?

  Perform reprecipitation to lower contaminant concentration
• How can occlusion be minimized?

  Perform digestion to allow particle growth
• What is the purpose of digestion in gravimetry?

  To allow small particles to grow larger
• What is the solid but porous body made by sintering glass particles called?

  Frit
• What is the purpose of the perforated base in a Gooch porcelain crucible?

  To hold asbestos pulp for filtration