DM.3

Question 1

What chemical property of transition metals is related to their colours?

Answer 1

partially filled d-orbitals of the metal ions.

Question 2

What colour does Fe2+ ions give in solution?

Answer 2

Green.

Question 3

What colour does Fe3+ ions give in solution?

Answer 3

Orange/brown.

Question 4

What colour does Cu2+ ions give in solution?

Answer 4

Blue.

Question 5

In terms of absorbance and transmission, when will a substance appear coloured?

Answer 5

When it absorbs or transmits light in the visible region, the substance will appear coloured.

Question 6

What happens when solutions of sodium hydroxide or ammonia are added to solutions containing transition metal ions?

Answer 6

They will form coloured precipitates of metal hydroxide complexes.

Question 7

Which metal hydroxide precipitate will redissolve if excess ammonia solution is added?

Answer 7

Cu(OH)2, it will give a deep blue-purple solution. This solutions then contains a copper ammonia complex.

Question 8

Will either iron(II) or iron(III) hydroxide dissolve in excess ammonia?

Answer 8

No, because they do not form complexes with ammonia.

Question 9

In terms of energy and electrons, when is light absorbed by an atom?

Answer 9

Light is only absorbed by an atom when the energy of the light matches the energy gap between two energy state in the atom. If it does, an electron will be excited from an orbital will a lower energy to one will a higher energy. By absorbing the light energy, the atom moves from its group state to the excited state.

Question 10

How can you find out the frequency of the light absorbed?

Answer 10

ΔE = hv where v is the frequency of the light and h is plank’s constant.

Question 11

What causes splitting of transition metal’s d orbitals?

Answer 11

Ligands surrounding the metal ion.

Question 12

Why does the splitting of d orbitals result in coloured transition metal complexes?

Answer 12

This is because the difference between the two d orbital ΔE caused by splitting matches the absorption of visible light.

Question 13

What colour is seen in terms of absorption and transmission?

Answer 13

The colour of the absorption is not seen, the complementary colour, which is reflected or transmitted is seen.

Question 14

What does the colour of the transition metal complexes depend on?

Answer 14

The types and numbers of ligands that surround the metal ion, which causes characteristic splitting patterns and therefore colour.

Question 15

What are ligands?

Answer 15

Ligands are negative ions or molecules that can donate a pair of electrons to form a covalent bond with a metal ion. They are similar to nucleophiles in organic chemistry.

Question 16

How are ligands attached to the metal ion?

Answer 16

They form a dative covalent bond with the metal ion using a lone pair of electrons.

Question 17

What are dative bonds also known as?

Answer 17

Coordinate bonds.

Question 18

Why can’t s block metal ions (group 1 and 2) form complexes with ligands?

Answer 18

Because they cannot accept dative bonds, it would be too many electrons for them. Water will form ion dipole interaction with them.

Question 19

What are some examples of things that can act as ligands?

Answer 19

H2O
OH-
NH3
CN-
CH3COO- (ethanoate)
Halides (Cl-,Br-,I-)
H2NCH2CH2NH2 (1,2-diaminoethane)

Question 20

What is a ligand called when it can form only one dative bond to the metal ion?

Answer 20

Monodentate ligand.

Question 21

What is a ligand called when it can form two dative bonds to the metal ion?

Answer 21

Bidentate ligand.

Question 22

What colour is vanadium in the +5 oxidation state?

Answer 22

Yellow

Question 23

What colour is vanadium in the +4 oxidation state?

Answer 23

Blue

Question 24

What colour is vanadium in the +3 oxidation state?

Answer 24

Green

Question 25

What colour is vanadium in the +2 oxidation state?

Answer 25

Purple

Question 26

What are the four things that effect the splitting of the d-obrbital and therefore the colour?

Answer 26

1. The metal ion
2. The oxidation state of the metal
3. The number and type of ligand involve
4. The shape of the complex

Question 27

What is a technique used to find the concentration of a coloured solution?

Answer 27

Colorimetry.

Question 28

How should you choose a filter for colourimetry?

Answer 28

You should choose a colour that corresponds to the colour of light that is most strongly absorbed by the solution.

Question 29

What is the relationship between absorbance and the concentration of a coloured solution?

Answer 29

A = kc, where A is absorbance and c is concentration. They are directly proportional, and k is a constant. This means as the concentration of the coloured solution increases, its absorbance will increase.