3.2.5.4 Formation of Coloured Ions

Question 1

What is colour caused by?

Answer 1

The compounds absorbing energy that corresponds to light in the visible region of the spectrum

Question 2

What causes a purple colour?

Answer 2

Absorption of all light but red and blue

Question 3

How are transition metals linked to colour?

Answer 3

The presence of a transition ion or metal in a compound or complex gives a colour

Question 4

What causes a colour in transition metals?

Answer 4

A partially filled d subshell

Question 5

How is the d subshell in transition metals split?

Answer 5

Two sets of orbitals

Ground state and excited state which differ in energy

Question 6

How does light affect the d subshell?

Answer 6

Energy in the visible spectrum causes electrons to jump from ground state orbitals to an excited state at a higher energy level

Question 7

How does colour relate to the absorption of frequencies of light?

Answer 7

The complimentary colour (frequencies which are not absorbed) is observed as they are reflected or transmitted

Question 8

Why do different transition ligands create different colours?

Answer 8

Different metal ions and different charges of the ions of the same metal and different ligands cause different splitting of the d subshell
This causes different visible light frequencies being absorbed which changes the observed colour

Question 9

What changes the splitting of the d subshell to change and therefore affects the colour observed?

Answer 9

Different ligands of the same metal ion
Different charges of the ions of the same metal
Different metal ions
The shape of the complex
The coordination number

Question 10

How do you work out the energy difference in electrons between the ground state and excited state?

Answer 10

/\E = hv
E = energy in joules
h = Planck's constant (6.63 x 10(-34))
v = frequency in hertz of the light absorbed

Question 11

How is a colorimeter used to detect transition metals?

Answer 11

It can find the ratio of metal ions to ligands in a complex
This gives the formula of the complex
A metal and ligand solution are mixed in different proportions
When they are mixed in the correct ratio, there is the maximum concentration of complex in the solution
This is when the solution will absorb the most light

Question 12

What is the equation linking wavelength to frequency?

Answer 12

c = v x lambda ( /\ )
c = speed of light
v = frequency of light in hertz
Lambda = wavelength in metres