Formation of coloured ions

How can transition metals be identified?

• By their colour

• Which depends on, coordination number, type of ligand and oxidation state

Colour arises when…

• Some of the wavelengths of visible light are absorbed

• And the remaining wavelengths of light are transmitted or reflected to the human eye

• Reflected wavelengths correspond to a specific colour

Change in energy

• Move from a ground state to an excited state when light is absorbed

• Change in energy (ΔE) can be calculated with

• ΔΕ = hv = hc/λ

• v = frequency in Hz

• λ = wavelength

• h = Planck’s constant

Colorimetry

• Uses absorption of visible light to determine concentration of coloured ions

• A calibration graph is produced by measuring solutions of known concentrations

• Which can then be used to calibrate the colorimeter on a graph of relative absorbance against concentration

• Can then be used to find the concentration of an unknown substance