Formation of Coloured Ions (Booklet 2) Flashcards
When light frequencies are absorbed do we see them ?
NO
Some light frequencies are transmitted or reflected do we see them ?
YES
Explain electron transitions in complexes
Presence of ligands causes d-subshell into split into two orbitals that have a distinct difference in energy between them
Electrons can be promoted from the ground state to the excited state by absorbing some frequencies of visible light
The colour seen is due to frequencies of light not absorbed
What is the lower energy d orbital known as ?
Ground state
What is the higher energy d orbital known as ?
Excited state
How does the colour of transition metal ion complexes arise ?
Electron transitions from one d orbital to another caused by the absorption of visible light
The frequency of light absorbed is related to what equation ?
AE=hv where A is delta
h=plancks constant (6.63x10-34)
v=frequency of the light Hz
AE= energy absorbed by excited electrons in J
The colour seen is due to frequencies of light not absorbed So if the colour blue is seen, then what does this mean ?
The colour blue has been transmitted
With reference to electrons explain why aqueous Cobalt (II) ions are pink
d electrons absorb light of a particular frequency (i.e blue in this case)
and are promoted to higher energy d orbitals
the colour not absorbed is the light transmitted through the sample
Pink light has not been absorbed
Why do complexes of magnesium , aluminium and zinc all appear colourless in solution
not transition metals, so no partially filled d sub-shells
so they transmit all frequencies of visible light
In terms of electrons explain why {Cr(H20)5Cl}3+ is red but {Cr(H20)5Cl}2+ is green
Cr3+ has the same number of d electrons
BUT
different ligands are present
SO
d-orbitals are split differently
different frequency of light absorbed SO
different frequency of light is transmitted through the sample.
What are the three main factors which affect the colour of transition metal complexes ?
the oxidation state of the ion
which ligands are present
coordination number of the complex
What is used to measure the colour intensity of a sample ?
How does it work ?
Colorimeter
Works based upon the fact that the intensity of colour in a solution is directly proportional to the concentration of the coloured species
Explain how you would determine the concentration of a transition metal ion.
Visible light is passed through the metal ion solution (to find the wavelength at which the absorbance is at its maximum)
Set the colorimeter to this wavelength
Make a series of standard solutions of the metal ion of known concentration
Add EDTA ligand to intensify colour
Measure the absorbance of the standard solutions and plot a graph of absorbance against concentration.
Measure the absorbance of the unknown and determine its concentration from the calibration curve.
What is the colour of Fe2+ ?
green (2 e’s in green)
