Chapter 23 - Transition Metals

Question 1

Why do transition metals behave so differently to group 1 and 2 metals?

Answer 1

Transition metals have access to incomplete d orbitals

Question 2

What do the properties of transition metals include?

Answer 2

Coloured ions
Variable oxidation states
Ability to form complexes
Catalytic activity

Question 3

What is a ligand?

Answer 3

A ligand is a molecule or ion capable of forming a dative bond with a transition metal by donating 2 electrons

Question 4

What is a complex?

Answer 4

A complex is a central transition metal ion or atom with dative bonds to ligands

Question 5

What is the co-ordination number of a complex?

Answer 5

The co-ordination number is the number of dative bonds present in a complex

Question 6

What are monodentate ligands?

Answer 6

Ligands which can only form one dative bond with a transition metal

Question 7

What are three examples of monodentate ligands?

Answer 7

Ammonia (NH3)
Water (H2O)
Cl-

Question 8

What can the monodentate ligands H20 and NH3 do due to their properties?

Answer 8

Out of the three common monodentate ligands, ammonia and water are fairly similar due to their same and neutral charge, therefore they can easily be substitued without changing co-ordination number of charge of the complex. This substitution can be complete or incomplete (all ligands or substituted or only some of them)

Question 9

What happens if ammonia or water is substituted by chloride ion

Answer 9

Usually, the chloride ion ligands will result in lower co-ordination numbers due to its increased size and charge

Question 10

What are bidentate ligands? Give two examples

Answer 10

Bidentate ligands are able to form 2 dative bonds with the central transition metal.
Ethylenediamine (H2NCH3CH3NH2)
Ethanedioate (C2O4-)

Question 11

What is a multidentate ligand? Give one example

Answer 11

Ligand capable of forming more than 2 dative bonds.
EDTA(4-) is capable of forming 6 dative bonds

Question 12

What is haem?

Answer 12

A Fe2+ compex with a multidentate ligand

Question 13

Why does the structure of haem make carbon monoxide so dangerous for humans?

Answer 13

Because carbon monoxide is capable of performing ligand substitution with oxygen and therefore oxygen cannot be transported

Question 14

What is the chelate effect and why does it occur?

Answer 14

Multidentate will replace bidentate ligands and bidentate replace monodentate ligands. They do this because it is entropically favourable as one bidentate takes the place of 2 monodentate, increasing the number of particles in solution

Question 15

What shape is often formed by complexes with H2O and NH3 ligands?

Answer 15

Octahedral

Question 16

What type of isomerism do octahedral complexes with monodentate ligands form?

Answer 16

cis-trans isomerism

Question 17

What type of isomerism do octahedral complexes with bidentate ligands form?

Answer 17

Optical isomerism

Question 18

What shape do Cl- ligands typically form? What shape can also be formed and what can it express?

Answer 18

Tetrahedral, however square planar can sometimes form and they express cis-trans isomerism, e.g cisplatin

Question 19

What linear complex is commonly used as a reagent?

Answer 19

Tollen’s reagent, a complex of silver with 2 ammonia ligands

Question 20

Why do ions form coloured solutions?

Answer 20

When visible light is absorbed by electrons and used to promote them into higher d orbitals, the energy is therefore absorbed by the ion and the other wavelengths are transmitted, forming a coloured solution

Question 21

How can you calculate the energy difference between ground state and excited electrons?

Answer 21

DeltaE (change in energy) = hv = hc/lambda

Question 22

What leads to a change in colour of an ion?

Answer 22

Change in oxidation state, ligand type or co-ordination number will all change DeltaE and therefore colour of ion

Question 23

How can coloured ions be used by chemists?

Answer 23

It can be used in spectroscopy, with simple colourimetry being able to determine concentration of coloured ions in solution

Question 24

Which transition metal can be reduced by zinc in acidic solution from its 5+ ion, what states is it changed to?

Answer 24

Vandate (V) ions are reduced to vanadium (IV), (III) and (II) ions

Question 25

Which two factors affect the ability of transition metal ions to go from a higher to lower oxidation state?

Answer 25

pH and type of ligand

Question 26

Which pH conditions favour which oxidation states?

Answer 26

Alkaline - oxidation
Acidic - reduction

Question 27

What is a heterogenous catalyst?

Answer 27

A catalyst in a different state as the reactants, and functions by adsorbing the reactants to its surface, pressuring the bonds allowing them to break more easily. An example of this is a catalytic converter

Question 28

What is a support medium for heterogenous catalysts?

Answer 28

It is a surface which the catalyst can be added to, to maximise surface area and therefore increase effectiveness, such as the ceramic honeycomb lattice in catalytic converters

Question 29

What can reduce efficiency of heterogenous catalysts?

Answer 29

They can become “poisoned” by impurities which block the active sites of the catalysts and don’t unbind

Question 30

What is the catalyst used in the Contact process, give the reactions it is used in

Answer 30

V2O5, acting as a heterogenous catalyst
SO2 + V2O5 -> V2O4 + SO3(useful product - used to make sulfuric acid)
2V2O4 + O2 -> 2V2O5 (catalyst regenerated)

Question 31

Which catalyst is used in the Haber process?

Answer 31

Iron

Question 32

What is a homogenous catalyst, and how do they work?

Answer 32

A homogenous catalyst is a catalyst in the same state as the reactants, and instead reacts with the reactants to form an intermediate process which is energetically favourable

Question 33

Which catalyst is used in the reaction between Iodide ions and peroxdisulfate ions, give equations

Answer 33

Iron(II)
S2O8 2- + 2Fe 2+ -> 2SO4 2- + 2Fe 3+
2Fe 3+ + 2I - -> 2Fe 2+ + I2

Question 34

What is autocatalysis?

Answer 34

Where a product is able to catalyse the reactants of the reaction

Question 35

Give an example of an autocatalysed reaction. Give the non catalysed reaction and the two catalysed reactions

Answer 35

The reaction between ethanedioate and potassium manganate, because the Mn2+ ions released in the reaction will catalyse the reactions
2MnO4(-) + 16 H+ + 5C2O4 (-) -> 2Mn(2+) + 8H2O + 10CO2

4Mn(2+) + MnO4(-) + 8H+ -> 5Mn(3+) + 4H2O
2Mn(3+) + C2O4(-) -> 2CO2 + 2Mn(2+)