chemical analysis

• what is a pure substance?

  one that only contains one compound or element throughout
• how can you test purity using bp/ mp ?

  • a chemically pure substance will melt/ boil at a specific temperature
  • you can test the purity of a sample by measuring its melting or boiling point and comparing it to that of the pure substance (which can be found in a data book)
  • impurities in a sample will lower the melting point and increase the melting range of your sample
• what are formulations?

  useful mixtures with a precise purpose that are made by following a formula

  each component is present in a measured quantity and contributes to the properties of the formulation so that it meets its required function
• what is the mobile phase (in chromatography)?

  where the molecules can move, always a liquid or a gas
• what is a stationary phase (in chromatography)?

  where the molecules cant move, can be a solid or a really thick liquid
• what is the flame emission spectroscopy?

  a method of analyzing the composition of a sample by heating it in a flame and observing the light emitted by the sample
• metals ions on the flame emission spectroscopy

  • a sample is placed into the flame
  • the ions become 'excited' and when they drop back down to their original energy levels they transfer energy as light
  • the light passes through a spectroscope, which can detect different wave lengths to produce a line spectrum
  • the combination of wavelengths emitted by an ion depends on its charge and its electron arrangement, since no 2 ions have the same charge and the same electron arrangement, different ions emmit different wavelengths of light
• the intensity of the spectrum indicates the concentration of that ion in solution
• flame emission spectroscopy can also be used to identify different ions in mixtures, this makes it more useful than flame tests, which only work for substances that contain a single metal ion
• machines can analyse unknown substances:

  • chemists often use instrumental analysis (i.e tests that use machines) , such as flame emission spectroscopy instead of conducting tests
  • advantages of using machines:
  • very sensitive- they can detect even the tiniest amount of substances
  • very fast and tests can be automated
  • very accurate