TM: Coloured ions
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What causes colour changes to arise?
Oxidation state Coordination number Ligand
Energy difference between d orbitals equation
ΔE = hf = hc / λ ΔE = Gap in energy in d orbitals (J) h = Planck’s constant f or v = frequency of light (s-1) c = velocity of light λ = wavelength (m)
How does colour arise
Some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected
Why is ΔE created
d electrons move from the ground state to an excited state when light is absorbed corresponding to the UV light absorbed
How does visible spectroscopy occur
Light is passed through and some is absorbed. Amount of light absorbed is proportional to concentration of the absorbing species.
What are some transition metal ions colourless / white [2]
[1] Full 3d subshell [2] Cannot absorb any light wavelengths
Explain why electron transition causes a solution containing a transition metal ion to become coloured [2]
[1] Light is absorbed [2] Remaining wavelength is transmitted
Calculate the volume of water that should be added to 100cm3 of a 0.1moldm-3 of iron(III) sulfate to make a 0.04 moldm-3 solution. [2]
[1] Total volume = (100 × 0.1) / 0.04 = 250 (cm3) [2] Therefore add 150 cm3
Write two equations to show how the autocatalyst is involved in this reaction [2]
[1] MnO4– + 8H+ + 4Mn2+ 5Mn3+ + 4H2O [2] 2Mn3+ + C2O42– 2Mn2+ + 2CO2
Aq copper(II) ions [Cu(H2O)6]2+ are blue. With reference to electrons, explain why aq copper(II) ions are blue. [3]
[1] absorbs (certain frequencies of) (white) light / [2] d electrons excited / move between orbitals [3] the colour observed is the light not absorbed / light reflected / light transmitted
A solution of KMnO4 has an uknown concentration. Describe briefly how colorimetry can be used to determine the concentration of this solution. [3]
[1] Make some known concentrations [2] Plot a graph of absorbance vs concentration [3] Read/compare unknown concentration from calibration curve/graph
During colorimetry, what colour filter paper do you use and why?
Filter colour opposite to the solution. Ensured that the wavelength of light is absorbed and not trasmitted to become visible light.
In colourimetry, what does a darker sample mean?
More concentrated so will have a higher absorbance of light.
What causes a change in oxidation state during a ligand substitution reaction
Electrons in the d-orbitals are repelled by electrons from incoming ligands