Transition metal introduction to colour

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  • Transition Metal Colour determination
    • Factors affecting colours
      • The colour of a transition metal compound is determined by the difference in energy between its d orbitals
        • Size and type of ligand
        • Strength of metal-ligand bonds
        • Complex shape
        • Co-ordination number
        • Oxidation state
    • Determining concentration
      • Ultraviolet–visible spectroscopy can be used to determine the concentration of a transition metal complex solution
        • It passes different frequencies of light through a sample
          • The amount of light absorbed is proportional to the concentration of the absorbing species
        • A number of solutions of complex are made up to known conc and placed in a spectrometer
          • Different frequencies of light are directed, and absorbance at each frequency is measured - the highest  absorbency is plotted on a calibration graph
            • A solution of known concenteations tested in turn for max absorbance at the relevant wavelength
              • These are recorded on a graph: max absorbance v conc
                • Unknown conc tested, marked on graph and estimated concentrationis read off the graph
      • A colorimeter can also be used to measure the concentration of a complex ion solution
        • Colorimeters only measure the absorbance of a specific frequency of light rather than the spectrum measured by UV-Vis spectrometers
          • They basically work in the same way as ultraviolet visible spectroscopy
      • If  accurate quantitative determination of the concentration of the solution is difficult, the ligand may be replaced to change its colour and increase its absorbance
  • A number of solutions of complex are made up to known conc and placed in a spectrometer
    • Different frequencies of light are directed, and absorbance at each frequency is measured - the highest  absorbency is plotted on a calibration graph
      • A solution of known concenteations tested in turn for max absorbance at the relevant wavelength
        • These are recorded on a graph: max absorbance v conc
          • Unknown conc tested, marked on graph and estimated concentrationis read off the graph

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