transition metals [I2] PAPER 1

Question 1

Explain why complexes formed from transition metal ions are coloured.

Answer 1

• absorbs wavelengths of visible light, which excites electrons in d-orbitals
• remaining wavelengths of visible light are reflected

Question 2

Copper(I) iodide is a white solid. Explain why copper(I) iodide is white.

Answer 2

• full d shell
• no d-d transitions possible / cannot absorb visible light

Question 3

what is a transition metal?

Answer 3

incomplete d shell

Question 4

general properties of a transition metal?

Answer 4

• form complexes
• form coloured ions
• have variable oxidation states
• good catalysts

Question 5

what is a ligand?

Answer 5

molecule/ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons

Question 6

what is a complex?

Answer 6

a central metal atom/ion surrounded by ligands

Question 7

what is co-ordination number?

Answer 7

number of co-ordinate bonds to the central metal atom/ion

Question 8

examples of some monodentate ligands?

Answer 8

H2O, NH3, Cl–

Question 9

why does a change in coordination number arise when the ligands NH3/H2O are exchanged with Cl– ?

Answer 9

Cl– ligand is larger than NH3/H2O ligand

Question 10

examples of bidendate ligands?

Answer 10

• H2NCH2CH2NH2
• C2O4–

Question 11

example of a multidentate ligand?

Answer 11

EDTA4–

Question 12

what is the chelate effect?

Answer 12

• bidentate/multidentate ligands replace monodentate ligands in a ligand substitution reaction
• in ligand substitution reactions, a positive entropy change is favoured and is achieved in this way (hence the reaction is more feasible), since it means a more stable complex is formed

Question 13

example of a complex with multidentate ligands?

Answer 13

• haem - iron (II) complex with a multidentate ligand

Question 14

why is carbon monoxide toxic?

Answer 14

• oxygen forms a co-ordinate bond to Fe (II) in haemoglobin, which allows oxygen transport in the blood
• carbon monoxide replaced oxygen that is co-ordinately bonded to Fe (II) in haemoglobin

Question 15

what shape are the complexes commonly formed by transition metals with small ligands, e.g. H2O and NH3 ?

Answer 15

octahedral

Question 16

octahedral complexes can display _____ isomerism with monodentate ligands

Answer 16

cis-trans

Question 17

octahedral complexes can display _____ isomerism with bidentate ligands

Answer 17

optical

Question 18

what shape are the complexes commonly formed by transition metals with larger ligands, e.g. Cl– ?

Answer 18

tetrahedral

Question 19

Ag+ always forms ____ complexes

Answer 19

linear

Question 20

what complex of Ag+ is used in Tollens’ reagent?

Answer 20

[Ag(NH3)2]+

Question 21

an exchange in ligands in a complex is a ____ reaction

Answer 21

ligand substitution

Question 22

why is the overall enthalpy change for ligand substitution reactions near zero?

Answer 22

same/very similar number and type of bond being broken and made

Question 23

platinum and nickel form ____ complexes, e.g. _____

Answer 23

• square planar
• cisplatin

Question 24

The energy difference between the ground state and the excited state of the d electrons is given by:

Answer 24

ΔE = hv = hc/λ

• ΔE = energy difference
• h = Planck’s constant
• c = speed of light
• v = frequency
• λ = wavelength

Question 25

what can lead to a change in colour of a complex?

Answer 25

• change in oxidation state • change in ligand • change in co-ordination number

Question 26

how are different species of vanadium with variable oxidation states formed?

Answer 26

oxidation of vanadium by zinc in acidic solution

Question 27

vanadium oxidation states and colours?

Answer 27

Question 28

acidity of transition metal complex ions in aqueous solution?

Answer 28

greater charge density of the metal ion means they polarise water molecules more, so more O–H bonds in ligands break to release H+ ions, lowering the pH

Question 29

what is a multidentate ligand?

Answer 29

molecule/ion that forms many co-ordinate bonds with the central metal ion

Question 30

what is a bidentate ligand?

Answer 30

molecule/ion that forms two co-ordinate bonds with the central metal ion

Question 31

what is a monodentate ligand?

Answer 31

molecule/ion that forms one co-ordinate bon with the central metal ion

Question 32

Answer 32

Question 33

Answer 33

Question 34

Describe how a calibration graph is produced and used to find the concentration of the iron(Ill) complex.

Answer 34

• measure absorbance for a range of known concentrations • plot graph of absorbance (y axis) against concentration (x axis) • read value of concentration for the measured absorbance from this graph

Question 35

Answer 35

B as only one with an incomplete d shell

Question 36

Answer 36

A - no lone pair

Question 37

Answer 37

Question 38

Solution A contains the compound [Cu(H2O)6]Cl2. State why the chloride ions in this compound are not considered to be ligands.

Answer 38

chloride ions isn’t forming a co-ordinate bond to Cu2+

Question 39

Answer 39

Question 40

how can vanadium be reduced from oxidation states 4, to 3, then 2?

Answer 40

reduction of vanadate (V) ions by zinc in acidic solution

Question 41

redox titration equations for Fe2+ and C2O4- with MnO4- ?

Answer 41

Question 42

what is a heterogeneous catalyst?

Answer 42

a catalyst that is in a different phase from the reactants

Question 43

How does iron act as a heterogeneous catalyst in the Haber process?

Answer 43

• reactants adsorb onto the surface / active sites of iron • bonds weaken and the reaction takes place • products desorb from the surface of the iron

Question 44

factors that affect the lifetime and efficiency of a catalyst?

Answer 44

• large surface area by using powder/ small pellets/support medium • catalyst poisoned (e.g. sulfur binds to the catalyst) - blocks the active site

Question 45

Answer 45

two negative ions repel, so activation energy is high

Question 46

Give a reason why Zn2+ ions do not catalyse the reaction.

Answer 46

Zn ions have only one oxidation state

Question 47

what colour is MnO4– ?

Answer 47

deep purple

Question 48

what colour is Mn2+ ?

Answer 48

pink

Question 49

why are transition metals with transition metal compound said to be self-indicating?

Answer 49

usually involves a colour change as metal is changing oxidation state

Question 50

what happens to aqua metal ions in acidic conditions?

Answer 50

they get reduced

Question 51

what happens to aqua metal ions in alkaline conditions?

Answer 51

they get oxidised

Question 52

the redox potential for a transition metal changing from a higher to lower oxidation state is influenced by…

Answer 52

• pH • ligand

Question 53

why are transition metals good catalysts?

Answer 53

exist in variable oxidation states, so provide alternative pathways easily

Question 54

advantage of a heterogeneous catalyst?

Answer 54

no need for separation of products from the catalyst

Question 55

two reactions in the Contact process, which is catalysed by vanadium (V) oxide, V2O5 ?

Answer 55

overall reaction: 2SO2 (g) + O2 (g) → 2SO3 (g)

Question 56

what is a homogeneous catalyst?

Answer 56

a catalyst that is in the same phase as the reactants

Question 57

how do homogeneous catalysts work?

Answer 57

form intermediates to give a different reaction pathway with a lower activation energy

Question 58

Answer 58

Question 59

what is autocatalysis?

Answer 59

when the product of the reaction is also a catalyst for the reaction

Question 60

Answer 60

Question 61

what is the colour change seen at the end point of a redox titration of Fe2+ with MnO4– ?

Answer 61

colourless to pink

Question 62

Answer 62

• reactants adsorbed onto platinum surface • bonds weaken on the surface - reaction occurs • desorption of the product

Question 63

Answer 63

Question 64

Answer 64

Question 65

Answer 65

Question 66

Answer 66