CH23 Transition metals

Question 1

Define a transition metal

Answer 1

An element which forms at least 1 stable ion with a partially full d-shell of electrons

Question 2

Physical properties of transition metals

Answer 2

Metallic
Good conductors of heat and electricity
Hard - strong - shiny
High MP and BP
Low reactivity

Question 3

Uses of Iron

Answer 3

Vehicle bodies

Reinforce concrete

Question 4

Uses of titanium

Answer 4

Jet engine parts

Question 5

Uses of copper

Answer 5

Water pipes

Question 6

Chemical properties of transition metals

Answer 6

Variable oxidation states
Coloured
Good catalysts
Form complex ions

Question 7

Define complex ion

Answer 7

Central transition metal surrounded by ligands that are co-ordinate bonded to it

Question 8

Example of transition metals as catalysts

Answer 8

Iron - Haber process
Vanadium (V) oxide - Contact process
MnO2 - decomposition of H2O2

Question 9

Which electrons do transition metals lose first when forming ions

Answer 9

4s

Question 10

Define ligand

Answer 10

An ion or molecules with at least 1 pair of electrons, that donates them to a transition metal ion to form a co-ordinate bond and thus a complex ion

Question 11

Define monodentate ligand

Answer 11

A ligand that forms one co-ordinate bond to the central metal ion

Question 12

Define bidentate ligand

Answer 12

A ligand that forms 2 co-ordinate bonds to the central metal ion

Question 13

Define multidentate ligand

Answer 13

A ligand that forms 3 or more co-ordinate bonds to the central metal ion

Question 14

Examples of monodentate ligands

Answer 14

Cl-
H2O
NH3
CN-

Question 15

How many co-ordinate bonds does EDTA4- form

Answer 15

6

Question 16

Define coordination number

Answer 16

The number of co-ordinate bonds the metal ion has formed to surrounding ligands

Question 17

What is the Chelate effect

Answer 17

Chelate complexes with multidentate ligands are favoured over ligands with fewer co-ordinate bonds per molecule

Question 18

Explain Chelate effect in terms of entropy

Answer 18

Number of molecules increases when multidentate ligands, displace ligands that form fewer co-ordinate bonds per molecule
Significant increase in entropy and a more stable complex ion is formed

Question 19

What ion is formed when a transition metal dissolves ion water

Answer 19

Aqua ion
6 H2O ligands
Octahedral complex ion

Question 20

If a transition metal has 2 ligands what shape is it

Answer 20

Linear

Question 21

If a transition metal has 4 ligands what shape is it

Answer 21

Tetrahedral

Question 22

Exception to 4 ligand rule

Answer 22

Platin - square planar in cisplatin

Question 23

If a transition metal has 6 ligands what shape is it

Answer 23

Octohedral

Question 24

How can complex ions display E-Z isomerism

Answer 24

Ligands differ in the way that they are arranged in space. Same side or opposite sides of the metal ion
Applies to square planar and octahedral complex ions

Question 25

What happens to Co2+, Cu2+ and Fe3+ when Cl- ligands replace NH3 or H2O

Answer 25

Decreases from 4 to 6 as Cl- is much larger

Question 26

What is haem

Answer 26

A molecules that makes up protein chains Fe2+ metal ion Coordination number of 6

Question 27

How does haemoglobin transport O2

Answer 27

O2 forms weak coordinate bond | Bond breaks when cell is reached

Question 28

Why is CO toxic

Answer 28

Also bonds coordinately to Fe2+ | Stops O2 from bonding

Question 29

Why are transition metals coloured

Answer 29

Partially filled d-orbitals, electrons move between d-orbitals d-orbitals can split into energy levels Electrons absorb energy in form of photons and turn into an excited state moving to a higher energy level Energy of photon related to freq of light E = hf

Question 30

How to calculate ΔE from f and / or λ

Answer 30

ΔE = hf = hc / λ

Question 31

What affects colour of transition metal

Answer 31

ΔE affects frequency of absorbed photons, so determines colour ΔE is changed by oxidation state of the metal, number and type of ligands, shape and co-ordination number

Question 32

Oxidation number and colour for VO2 +, VO2+, V3+, V2+

Answer 32

VO2 + ==> 5+ , Yellow VO2+ ==> 4+, Blue V3+ ==> 3+, Green V2+ ==> 2+, Violet

Question 33

What is used to reduce vanadium

Answer 33

Zinc

Question 34

What colour is Fe2+ aqua ion

Answer 34

Green

Question 35

What colour is Fe3+ aqua ion

Answer 35

Pale brown

Question 36

What colour is Cr2+ aqua ion

Answer 36

Blue

Question 37

What colour is Cr3+ aqua ion

Answer 37

Red / violet

Question 38

What colour is Co2+ aqua ion

Answer 38

Brown

Question 39

What colour is Co3+ aqua ion

Answer 39

Yellow

Question 40

What does a colorimeter do

Answer 40

Measures absorbance of a particular wavelength of light by a solution

Question 41

How would you use colorimetry experimentally

Answer 41

Use solutions of known concentration to create a calibration graph; find unknown concentration

Question 42

What information can a colorimeter provide

Answer 42

Concentration of a certain ion

Question 43

Why can transition metals have variable oxidation states

Answer 43

They have partially filled d-orbitals, so can lose 4s and 3d electrons

Question 44

Which oxidation states do all transition metals have (except Sc) - why

Answer 44

+2 - Loss of electrons from 4s orbital

Question 45

When oxidation state is high, do transition metals exist as simple ions

Answer 45

No, they covalently bond to other species

Question 46

Use of complex [Ag(NH3)2]+ ion

Answer 46

Tollen's reagent to test for aldehydes / ketones

Question 47

What colour is MnO4-

Answer 47

Deep purple

Question 48

What colour is Mn2+

Answer 48

Pink

Question 49

Why are redox titrations with transition metals said to be self indicating

Answer 49

Usually involve a colour change due to change in oxidation state

Question 50

What colour is Cr2O7 2-

Answer 50

Orange

Question 51

What colour is Cr3+

Answer 51

Green

Question 52

What happens to aqua metal ions in acidic conditions

Answer 52

They get reduced

Question 53

What happens to aqua metal ions in alkaline conditions

Answer 53

They get oxidised

Question 54

What happens to aqua metal ions in neutral conditions

Answer 54

No change

Question 55

What does; whether reduction / oxidation occurs and the readiness of the raction depend on

Answer 55

E° values

Question 56

What can change these E° values

Answer 56

pH, ligands involved

Question 57

Define a catalyst

Answer 57

A substance that increases the rate of reaction without being chemically changed at the end of the reaction

Question 58

How do catalysts work

Answer 58

Provide an alternative reaction pathway with a lower activation energy

Question 59

Why are transition metals good catalysts

Answer 59

Exist in variable oxidation states, easily provide alternative pathways

Question 60

Why are group 1, 2 and 3 metals not good catalysts

Answer 60

Only exist in 1 oxidation state

Question 61

What are advantages of using a catalyst for a reaction

Answer 61

Allows reactions to proceed at lower temperatures and pressures

Question 62

What are used in a catalytic converter and which reactions do they catalyse

Answer 62

Platinum, Rubidium, Palladium | Catalyse CO and NO to CO2 and N2

Question 63

Define heterogenous catalyst

Answer 63

A catalyst that is present in the reaction in a different phase to the reactants Catalytic activity occurs on the solid surface as the reactants pass over it

Question 64

Advantage of using a heterogenous catalyst

Answer 64

No need for separation of products from catalyst

Question 65

How do heterogenous catalysts work

Answer 65

Reactants adsorb to the catalysts surface at active sites Weaken bonds within the reactants, holds reactants close together on surface to react Once reaction occurs products desorb

Question 66

What properties does the catalyst need to have

Answer 66

Can't adsorb too strongly - no release | Can't adsorb too weakly - no attachment

Question 67

How can you increase the efficiency of heterogeneous catalysts

Answer 67

Increase SA to increase number of active sites present | Also spread onto an inert support medium to increase surface area:mass ratio

Question 68

What is catalyst poisoning

Answer 68

Unwanted impurities adsorb to the catalyst's active sites and do not desorb

Question 69

What effect does this have

Answer 69

Decreases effectiveness of catalyst over time

Question 70

How else can a catalyst be degraded

Answer 70

Finely divided catalysts can be gradually lost from their support medium

Question 71

What is in the Haber process

Answer 71

Makes ammonia from nitrogen and hydrogen | Fe catalyst

Question 72

Size and shape of catalyst for Haber process

Answer 72

Pea sized lumps to increase SA

Question 73

How long until catalyst is poisoned in Haber cycle

Answer 73

5 years - poisoned by sulfur impurities in gas stream

Question 74

What is the Contact process

Answer 74

Makes H2SO4 from SO2 and O2 | Vanadium (V) oxide catalyst

Question 75

Why is V a good catalyst

Answer 75

Can change oxidation state

Question 76

Define homogenous catalyst

Answer 76

A catalyst in the same phase as the reactants

Question 77

How do they work

Answer 77

Form intermediates to give a reaction with lower activation energy

Question 78

Define autocatalysis

Answer 78

When a product of a reaction is also a catalyst