CHEM LAB

• Characteristics of organic compounds


  • Combustible
  • Non electrolyte
  • No sharp melting point
  • Decompose easily in high temperature
  • Insoluble
• Qualitative analysis

  • Analysis of the species of the given compound
  • Detection of various elements present in organic compounds
• Other common elements in organic compounds

  • Oxygen
  • Nitrogen
  • Halogens
  • Sulfur
  • Phosphorus
• Ignition test

  1. Combustion reaction occurs when a substance reacts with oxygen to release energy

  2. When methane burns it releases carbon dioxide and water
• Factors affecting solubility


  • Temperature
  • Polarity
  • Pressure
  • Molecular size
  • Surface area of Solute
• Electrical conductivity

  • The higher concentration of the ions, the greater conductivity
  • To determine if the compound can conduct a current is to identify its electrical current
• Sodium Fusion Test

  1. Use for detecting nitrogen, sulfur and halogens

  2. Test for nitrogen: Prussian blue test

  3. Test for halogens (nitrogen and sulfur is absent): Precipitate indicates the amount of halogens

  4. Test for halogens (nitrogen and sulfur is present): Acidify the fusion solution with dilute nitric acid, evaporate to remove hydrogen sulphide and hydrogen cyanide
• Test for carbon and hydrogen

  Detected by heating the compound with copper oxide
• Test for sulfur

  Acetic acid and lead acetate is added and black precipitate indicates the presence of sulfur
• Separation techniques

  • Filtration
  • Dialysis
  • Size exclusion
• Separation based on mass or density

  If the analyte and interference have different densities and masses the separation use is centrifugation
• Separations based on complex reaction (Masking)

  Binding the interferent in a strong, soluble complex that prevents it from interfering in the analyte's determination
• Change in physical state

  1. Distillation if the interference and analyte are miscible liquids with significantly different boiling points

  2. Sublimation if the sample is solid and the analyte can vaporize without passing through a liquid state

  3. Recrystallization to purify a solid
• Change in chemical state

  Precipitation reactions based on pH-dependent solubility of metal oxides, hydroxides, and sulfides
• Extraction between two phases

  Moving of the species from one phase to another phase
• Chromatographic separations

  • Separates analytes and interferents, and provides a means for qualitative or quantitative analysis
  • The sample is extracted into a mobile phase that is continuously passed over a stationary phase
  • Components with larger partition coefficients are more likely to move into the stationary phase and take longer to pass through the system
• Crystallization

  Formation of a new, insoluble product by a chemical reaction, which then precipitates out of the reaction solution as an amorphous solid containing many trapped impurities
• Recrystallization

  Does not involve a chemical reaction, the crude product is simply dissolved into solution and then the conditions are changed to allow crystals to re-form, producing a more pure final product
• Decolorization

  Removing brightly colored organic impurities from the sample mixture using decolorizing carbon or activated charcoal
• Separation by sublimation

  Gentle heating of the solid mixture in a confined container until the component with high vapor pressure changes into the vapor state, while the component with lower vapor pressure is left in the container
• Solvent extraction

  Like dissolves like, the "salting-out effect" can be used to decrease the solubility of non-polar components
• Chromatography

  • Separates the components or solutes of a mixture based on the relative amounts of each solute distributed between a moving fluid stream (mobile phase) and a contiguous stationary phase
  • The mobile phase may be either a liquid or a gas, while the stationary phase is either a solid or a liquid
  • Different travel times are termed retention time