15 - Transition Metals

Question 1

what is a transition metal

Answer 1

a metal that forms one or more stable ions with incompletely filled d orbitals

Question 2

why do transition metals show variable oxidation state

Answer 2

there is little energy difference between the 4s and 3d orbitals

Question 3

what is a ligand

Answer 3

the species that forms dative covalent (co-ordinate) bonds with a metal ion to form a complex ion

Question 4

bonding involved in a complex ion

Answer 4

co-ordinate or dative covalent

Question 5

what does the colour of aqueous ions come from

Answer 5

• ligand causes electron repulsion
• splits d orbitals into two energy levels
• gap in orbitals corresponds to wavelength of visible light
• visible light is absorbed by electrons, promotes them to a higher energy level
• wavelength of light not absorbed is reflected and colour is seen

Question 6

reasons for colour changes in aqueous complex ions

Answer 6

• oxidation number
• ligand
• co-ordination number

Question 7

why do some aqueous ions not have a colour

Answer 7

they do not have any/enough electrons in their d orbital, so can’t get promoted to higher energy levels

Question 8

what does co-ordination number mean

Answer 8

number of dative co-ordinate bonds that are formed

Question 9

ligands that form octahedral shaped complexes

Answer 9

• H2O
• OH-
• NH3

Question 10

ligands that form tetrahedral complexes

Answer 10

Cl- as it is relatively large

Question 11

example of square planar complex

Answer 11

cis platin

Question 12

how does cisplatin work

Answer 12

• passes through cell membrane, and ligand exchange with H2O happens
• water molecules bind to platinum more loosely than the chlorine was
• water molecule falls off and cisplatin binds to bases on DNA, kinking it and preventing it from replicating

Question 13

why does only cisplatin work, not a mixture of cis and trans

Answer 13

• trans has the wrong geometry

Question 14

bidentate ligand example

Answer 14

NH2CH2CH2NH2

Question 15

multidentate ligand example

Answer 15

EDTA 4- which is hexadentate

Question 16

what is haemoglobin

Answer 16

an iron (II) compound containing a multidentate ligand

Question 17

how does carboxyhaemoglobin form?

Answer 17

ligand exchange between oxygen bound to haemoglobin and carbon monoxide

Question 18

colour of Vanadium 5+ (VO2)+

Answer 18

yellow

Question 19

colour of Vanadium 4+ (VO)2+

Answer 19

blue

Question 20

colour of Vanadium 3+ V3+

Answer 20

green

Question 21

colour of Vanadium 2+ V2+

Answer 21

violet

Question 22

how are dichromate(VI) ions reduced

Answer 22

by Zn ions in acidic conditions, to Cr3+ and Cr2+

colour change from orange to green to blue

Question 23

how are dichromate(VI) ions produced

Answer 23

by adding H2O2 to Cr3+ or Cr2+ in alkaline conditions, followed by acidification

Question 24

how are dichromate (VI) ions converted to chromate(VI) ions

Answer 24

2(CrO4)2− + 2H+ ⇌ (Cr2O7)2− + H2O

Question 25

what leads to a more stable complex ion and why?

Answer 25

- substituting a less / monodentate ligand for a more / multidentate one - this increases the moles of product formed, increasing the entropy of system

Question 26

what leads to a change in co-ordination number

Answer 26

substituting smaller uncharged ligands like H2O for larger charged ones like Cl-, as there is more electron repulsion. Normally decreases co-ordination number

Question 27

what can transition metals and their compounds acts as

Answer 27

homo and heterogeneous catalysts

Question 28

what is a heterogeneous catalyst

Answer 28

a catalyst in a different phase from the reactants and the reaction occurs at the surface of the catalyst

Question 29

three examples of ligand exchange and their colour changes

Answer 29

[Cu(ΝΗ3)4(Η2Ο)2]2+ from [Cu(Η2Ο)6]2+ via Cu(OH)2(Η2Ο)4 pale blue solution to dark blue solution [CuCl4]2− from [Cu(Η2Ο)6]2+ pale blue solution to yellow solution [CoCl4]2− from [Co(Η2Ο)6]2+ pink solution to blue solution