D-block Transition Metals

Question 1

What are the common oxidation states of chromium?

Answer 1

+6 and +3

Question 2

What are the common oxidation states of manganese?

Answer 2

+2, +4 and +7

Question 3

What are the common oxidation states of iron?

Answer 3

+2 and +3

Question 4

What are the common oxidation states of copper?

Answer 4

+1 and +2

Question 5

Why do transition metal compounds have variable oxidation states?

Answer 5

The ionisation energies for d-orbitals are similar

Question 6

Explain the catalytic properties of transition metals and give two examples

Answer 6

Transition metal compounds can act as catalysts because they have partially filled d-orbitals and variable oxidation states. This means they can adsorb reactant molecules and initiate a reaction.
Examples:
> Vanadium (V) oxide in the contact process
> Titanium Chloride in the polymerisation of ethene
> Nickel or platinum in the hydrogenation of alkenes
> Iron in the Haber process

Question 7

1 use of transition metals in biological systems

Answer 7

1. Iron in haemoglobin

2. Cobalt as a component of vitamin B-12

Question 8

1 use of transition metals in industry

Answer 8

1. Chromium as a component of stainless steel
2. Iron used in iron and steel manufacture
3. Copper used in circuitry and electronics

Question 9

What is a ligand?

Answer 9

A small molecule with a lone pair which can bond to a transition metal (e.g. Water or ammonia)

Question 10

Define monodentate

Answer 10

This is a ligand that has one atom that can bond to a transition metal ion

Question 11

Define bidentate

Answer 11

This is a ligand that has two atoms that can bond to a transition metal ion

Question 12

What is the colour and shape of [Cu(H2O)6]2+?

Answer 12

Shape : octahedral complex

Colour : pale blue

Question 13

What is the colour and shape of [ Cu(NH3)4(H2O)2]2+?

Answer 13

Shape : octahedral complex

Colour : royal blue

Question 14

What is the colour and shape of [CuCl4]2-?

Answer 14

Shape : tetrahedral complex

Colour : yellow-green

Question 15

Explain how colour arises in transition metal complexes

Answer 15

• When transition metals form complexes their d-orbitals split
• 2 have higher energy and 3 lower
• For electrons to move from the lower level to the higher they must absorb the correct energy
• This energy corresponds to a specific frequency of light
• The colour seen in due to the frequencies which are not absorbed

Question 16

Are all transition metal complexes coloured?

Answer 16

No, if the transition metal ion has full d-orbitals (Cu+) or empty ones (Sc3+, Ti4+) then electrons can’t move from lower levels to higher one and it is therefore colourless

Question 17

Reaction of chromium (III) ions with a little and with excess sodium hydroxide solution

Answer 17

Cr3+ solution ~ green
Aqueous NaOH ~ grey-green ppt
Excess NaOH ~ green solution

Question 18

Reaction of iron (II) ions with a little and with excess sodium hydroxide solution

Answer 18

Fe2+ solution ~ pale green
Aqueous NaOH ~ dark green ppt
Excess NaOH ~ no change (dark green ppt)

Question 19

Reaction of iron (III) ions with a little and with excess sodium hydroxide solution

Answer 19

Fe3+ solution ~ yellow
Aqueous NaOH ~ red-brown ppt
Excess NaOH ~ no change (red-brown ppt)

Question 20

Reaction of copper (II) ions with a little and with excess sodium hydroxide solution

Answer 20

Cu2+ solution ~ blue
Aqueous NaOH ~ pale blue ppt
Excess NaOH ~ no change (pale blue ppt)

Question 21

Give the equation for chromium (III) ions with NaOH and excess NaOH

Answer 21

Aqueous NaOH : Cr3+ + 3OH- –> Cr(OH)3

Excess NaOH : Cr(OH)3 + 3OH- –> [Cr(OH)6]3-

Question 22

What is a transition element?

Answer 22

Elements with partially filled d-orbitals in their atoms or ions