formation of coloured ions

Question 1

why are transition metal ions coloured

Answer 1

some wavelengths of light are absorbed
which excites electrons in d orbitals
and the remaining reflected

Question 2

if a compound is blue what parts of the visible spectrum is it absorbing and reflecting?

Answer 2

if a compound appears blue it is absorbing all other parts of the visible spectrum but reflecting blue

Question 3

why are some wavelengths of light absorbed

Answer 3

d electrons move from a ground state to an excited state when light is absorbed

d electrons relax back to ground state by releasing thermal energy

Question 4

what is the equation to calculate the difference in energy between ground state and excited state is

Answer 4

change in E = hv or E = hc / theta
Changes in oxidation state, co-ordination number and ligand alter
E leading to a change in wavelength absorbed and therefore
colour

Question 5

how can colorimetry be used to determine the concentration of coloured ions in solution

Answer 5

1) make a series of dilutions of a standard solution of known
concentration

2) Find the absorbance using a colorimeter

3) Plot graph of absorbance vs. concentration and add a line of
best fit

4) Find absorbance of unknown sample

5) Use the graph to find concentration (read off the line on the
graph)

Question 6

why are transition metals coloured (3 marks)

Answer 6

• absorb some wavelengths
• excite electrons in d orbitals
• remaining wavelengths are reflected

Question 7

what is the plank constant

Answer 7

6.63 x 10 to power of -34 Js

Question 8

what is the speed of light

Answer 8

3.00 x 10 power of 8 ms^-1

Question 9

what is the equation that links

energy
frequency
plank constant

Answer 9

E = h f

Question 10

what is the equation that links energy , plank constant, speed of light and wavelenght

Answer 10

E = h x (c/λ)

Question 11

convert 490nm into metres

Answer 11

4.9 x 10 to the power of -7