A2- Transition Metals; colours

Question 1

Write an equation that links energy, frequency and the Plank constant

Answer 1

E = hf

Question 2

Write an equation that links energy, c, wavelength and the Plank constant

Answer 2

E = hc/λ

Question 3

Explain (briefly) why copper (II) sulfate solution is blue

Answer 3

absorbs other parts of the visible spectrum, reflects/transmits blue light

Question 4

Explain why transition metal ions absorb light in the visible part of the spectrum. You should refer to electron transitions in your answer

Answer 4

• d sub-shell orbitals have a ground and excited state
• electrons absorb light photons with energy equivalent to visible light (E= hf)
• promoted to excited state
• relax back an release thermal energy
• light not absorbed is reflected

Question 5

Give 3 factors that affect the colour of a transition metal

Answer 5

• coordination number
• ligands
• oxidation state

Question 6

Explain why [CuCl4]2- has a different colour to [Cu(H2O)6]2+

Answer 6

• different ligands and co-ordination number
• changes the energy gap between ground and excited state d sub-shell
  orbitals
• different frequency of light absorbed [E = hf)

Question 7

Explain why Cu+ ions do not form coloured solutions

Answer 7

do not have an INCOMPLETE d-subshell

Question 8

What can colorimetry be used to determine?

Answer 8

concentration of coloured ions

Question 9

How is colorimetry carried out to find concentration of coloured ions?

Answer 9

1) series of dilutions, with known concentrations
2) find absorbance using colorimeter
3) plot graph of absorbance vs conc and draw line of best fit
4) find absorbance of unknown sample
5) use graph