Transition metals

Question 1

What is a transition metal?

Answer 1

A transition metal is a metal that can form one or more stable ions with an incomplete d sub-shell

Question 2

What are the physical properties of transition metals?

Answer 2

• high density
• high melting and boiling points
• ionic radii is more or less the same

Question 3

What are the chemical properties of transition metals?

Answer 3

• complex formation
• formation of coloured ions
• variable oxidation state
• catalytic activity

Question 4

What is a ligand?

Answer 4

A ligand is a molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons

Question 5

Why are zinc and scandium not transition metals?

Answer 5

Their stable ions do not have incomplete d sub-shells
Scandium has an empty d shell
Zinc has a full d shell

Question 6

What is a complex?

Answer 6

A complex is a central atom or ion surrounded by ligands

Question 7

What is the co-ordinate number?

Answer 7

It is the number of coordinate bonds to the central metal atom or ion

Question 8

Give three examples of monodentate ligands

Answer 8

NH3
H2O
Cl-

Question 9

Why is there not a change in the coordination number when NH3 and H2O are substituted?

Answer 9

They are similar in size and are uncharged

Question 10

Give two examples of bidentate ligands

Answer 10

Ethane-1,2-diamine(en)

Ethanedioate

Question 11

Give an example of a multidentate ligand

Answer 11

EDTA(4-)

Question 12

What is haem?

Answer 12

It is an iron(II) complex with a multidentate ligand

Question 13

How is oxygen transported in the blood

Answer 13

Oxygen forms a coordinate bond with Fe(II) in haemoglobin

Question 14

Why is CO toxic to humans?

Answer 14

It forms a stronger coordinate bond with Fe(II) compared to oxygen. Therefore, it replaces the oxygen attaching to the haemoglobin

Question 15

What is the chelate effect?

Answer 15

The substitution of a monodentate ligand with a bidentate or multidentate ligand which leads to a more stable complex

Question 16

Explain the chelate effect in terms of enthalpy and entropy change

Answer 16

The enthalpy change is small a there is a similar number of bonds being made and broken
The entropy change is positive
Therefore, the free energy is negative

Question 17

Which shapes can be formed by complex ions?

Answer 17

Octahedral
Tetrahedral
Square planar
Linear

Question 18

Which complexes show cis-trans isomerism?

Answer 18

Square planar

Octahedral

Question 19

Which complexes show optical isomerism?

Answer 19

Octahedral

Question 20

Which factors lead to the colour change in transition metals?

Answer 20

Oxidation state
Coordination number
Ligands

Question 21

How does colour arise in coloured ions?

Answer 21

Colour arises from electronic transitions from the ground state to excited states.
A portion of visible light is absorbed and the light that is transmitted gives the coloured ion its colour.

Question 22

Give the equation that links the energy difference between the split d orbitals to the frequency of light absorbed

Answer 22

E=hv
E is the energy split
h is Planck’s constant
v is the frequency of the light absorbed

Question 23

Why does Sc3+ have no colour?

Answer 23

It has no electrons in the d shell. Therefore, there is no energy transfer.

Question 24

Why do Zn+2 and Cu+ ions have no colour?

Answer 24

The ions have full d shells. There is no space for electrons to transfer, therefore, there is no energy transfer.

Question 25

How can a simple colourimeter be used to determine the concentration of coloured ions in a solution?

Answer 25

When visible light is passed through a sample of a coloured complex ion, some of the light is absorbed. The amount of light absorbed is proportional to the concentration of the absorbing species.

Question 26

Which factors influence the redox potential for a transition metal ion changing from a higher to a lower oxidation state?

Answer 26

pH | Ligands

Question 27

What is the oxidation state of vanadium in VO2(+) and the colour of the solution?

Answer 27

+5 | yellow

Question 28

What is the oxidation state of vanadium in VO(2+) and the colour of the solution?

Answer 28

+4 | blue

Question 29

What is the oxidation state of vanadium in V(3+) and the colour of the solution?

Answer 29

+3 | green

Question 30

What is the oxidation state of vanadium in V(2+) and the colour of the solution?

Answer 30

+2 | violet

Question 31

What is the observation when [Ag(NH3)2]+ is used to distinguish aldehydes and ketones?

Answer 31

Aldehydes- silver mirror | Ketones- no visible change

Question 32

Why is an indicator unnecessary for the MnO4- and Fe2+ redox titration?

Answer 32

The titration is self indicating because of the significant colour change

Question 33

What is the colour change for the MnO4- and Fe2+ redox titration?

Answer 33

Purple to colourless

Question 34

Give the equation for the MnO4- and Fe2+ redox titration

Answer 34

MnO4-(aq) + 8H+(aq) + 5Fe(2+)(aq) → Mn2+(aq) + 4H2O(l) + 5Fe(3+)(aq)

Question 35

Which acid can only be used for manganate titrations?

Answer 35

dilute sulfuric acid

Question 36

What will happen when insufficient volumes of sulfuric acid are used?

Answer 36

the solution is not acidic enough MnO2 will be produced instead of Mn2+ the brown MnO2 will mask the colour change leading to a greater inaccurate volume of manganate being used

Question 37

Why can conc. HCl not be used in manganate titrations?

Answer 37

Cl- ions will be oxidised to Cl2 a greater volume of manganate used poisonous Cl2 gas produced

Question 38

Why can nitric acid not be used?

Answer 38

It is an oxidising agent It oxidised Fe2+ to Fe3+ a smaller volume of manganate used

Question 39

Give the overall equation for the manganate titration with hydrogen peroxide

Answer 39

2MnO4(-)(aq) + 6H+(aq) + 5H202 → 5O2 + 2Mn(2+)(aq) + 8H2O(l)

Question 40

Give the overall equation for the manganate titration with ethanedioate

Answer 40

2MnO4(-)(aq) + 16H+(aq) + 5C2O4(2-) → 10CO2 + 2Mn(2+)(aq) + 8H2O(l)

Question 41

What is a heterogeneous catalyst?

Answer 41

It is in a different phase from the reactants

Question 42

What is a homogeneous catalyst?

Answer 42

It is in the same phase as the reactants

Question 43

What are the steps in heterogeneous catalysis?

Answer 43

Reactants are adsorbed at active sites on the surface of the catalyst The bonds in the reactants weaken and break New bonds are formed between the reactants Then the product desorbs from the catalyst surface

Question 44

How is the surface are of a solid catalyst maximised?

Answer 44

A support medium is often used to maximise the surface area and minimise cost

Question 45

Give two reactions which show how V2O5 is used as a catalyst in the Contact Process

Answer 45

SO2 + V2O5 → SO3 + V2O4 V2O4 + 0.5O2 → V2O5

Question 46

How can the efficiency of heterogeneous catalysts be reduced?

Answer 46

Impurities block the active sites

Question 47

Why can transition metals act as homogeneous catalysts?

Answer 47

they can form various oxidation states | they are able to oxidise and reduce because of their partially filled d-shells

Question 48

Explain, with the aid of equations, how Fe2+ ions catalyse the reaction between I- and S2O8(2-).

Answer 48

S2O8(2-) + 2Fe(2+) → 2SO4(2-) + 2Fe(3+) 2I- + 2Fe(3+) → 2Fe(2+) + I2

Question 49

Explain, with the aid of equations, how Mn2+ ions catalyse the reaction between MnO4(-) and C2O4(2-).

Answer 49

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

Question 50

Why is the uncatalysed reaction slow?

Answer 50

The reaction involves a collision between two negative ions which repel each other leading to a high activation energy