LESSON 3- PRECIPITATION REACTIONS

• Types of chemical analysis

  • Classical analysis
  • Instrumental analysis
• Classical analysis


  Wet chemical analysis that uses no mechanical or electronic instruments other than analytical balance
• Instrumental analysis


  Involves the use of instruments other than analytical balance
• Both classical and instrumental analysis are quantitative analysis, and are divided into gravimetric and volumetric
• Gravimetric analysis


  Relies on a critical mass measurement
• Volumetric analysis


  Involves the measurement of a volume of a solution
• Precipitation reactions


  Two soluble compounds that form an insoluble solid when mixed in a solution
• Precipitate


  The product in precipitation that occurs when the product of the concentration exceeds the solubility of the product
• Precipitation


  The forming or the process of forming a solid from a solution
• Precipitant


  A chemical that causes a solid to form in a liquid solution, the reagent added to initiate the precipitation reaction
• Precipitate


  The solid substance that is formed when two solutions react to form an insoluble product
• Methods to recover a precipitate

  • Filtration
  • Centrifugation
  • Decantation
• Filtration


  A process that separates the insoluble solid from a liquid by passing the mixture through a filter
• Residue


  The insoluble solid left on the filter paper
• Filtrate


  The liquid that has passed through the filter paper
• Centrifugation


  Use spin sample very rapidly; the denser materials will form to the bottom
• Decantation of liquids


  Used to separate two liquids with different densities, e.g. oil and water
• Decantation of sediment


  Can also separate a liquid from heavy sediments that sink to the bottom of the container, e.g. stone and water
• Types of precipitates

  • Crystalline
  • Gelatinous
  • Curdy
• Crystalline precipitate


  Well defined, regularly shaped crystals; the shape is a function of the composition of a salt
• Gelatinous precipitate


  Flocculated colloids; jelly-like or hydrous masses that trap a great deal of water and many impurities
• Curdy precipitate


  Aggregates of small porous particles that are solid substances that form in a solution during precipitation reaction, characterized by the appearance of small irregular curds and lumps
• Crystalline


  ordered structured, well defined & ordered arrangement of atoms or molecules

  example: calcium oxalate & alkaline earth sulfates (barium sulfate)
• Curdy

  • aggregates of small porous particles
  • cation & anion reacts to form a soluble colloids & then coagulate into a filterable sized particle
  • they are very thick and reasonable in size (filtered rapidly, easy, & completely)
  • soft and friable texture and they may appear clumpy
  • example: sodium chloride & silver bromide
• Gelatinous


  • no ordered & periodic arrangement or structure; it lacks a well-defined structure
  • it is very difficult to work with
  • the cation & anion form a soluble colloid & then coagulate to filterable sized particles
  • example: metals hydroxides such as ferric hydroxid
• CURDY


  • silver halides compound
• GELATINOUS


  • metal hydroxide such as ferric hydroxide
• CRYSTALLINE


  • alkaline earth sulfate such as barium sulfate