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Chemistry > CH23 Transition metals > Flashcards

CH23 Transition metals Flashcards

1
Q

Define a transition metal

A

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

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2
Q

Physical properties of transition metals

A 
Metallic
Good conductors of heat and electricity
Hard - strong - shiny
High MP and BP
Low reactivity
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3
Q

Uses of Iron

A

Vehicle bodies

Reinforce concrete

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4
Q

Uses of titanium

A

Jet engine parts

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5
Q

Uses of copper

A

Water pipes

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6
Q

Chemical properties of transition metals

A

Variable oxidation states
Coloured
Good catalysts
Form complex ions

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7
Q

Define complex ion

A

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

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8
Q

Example of transition metals as catalysts

A

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

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9
Q

Which electrons do transition metals lose first when forming ions

A

4s

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10
Q

Define ligand

A

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

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11
Q

Define monodentate ligand

A

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

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12
Q

Define bidentate ligand

A

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

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13
Q

Define multidentate ligand

A

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

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14
Q

Examples of monodentate ligands

A

Cl-
H2O
NH3
CN-

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15
Q

How many co-ordinate bonds does EDTA4- form

A

6

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16
Q

Define coordination number

A

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

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17
Q

What is the Chelate effect

A

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

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18
Q

Explain Chelate effect in terms of entropy

A

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

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19
Q

What ion is formed when a transition metal dissolves ion water

A

Aqua ion
6 H2O ligands
Octahedral complex ion

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20
Q

If a transition metal has 2 ligands what shape is it

A

Linear

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21
Q

If a transition metal has 4 ligands what shape is it

A

Tetrahedral

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22
Q

Exception to 4 ligand rule

A

Platin - square planar in cisplatin

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23
Q

If a transition metal has 6 ligands what shape is it

A

Octohedral

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24
Q

How can complex ions display E-Z isomerism

A

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

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25
Q

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

A

Decreases from 4 to 6 as Cl- is much larger

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26
Q

What is haem

A

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

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27
Q

How does haemoglobin transport O2

A

O2 forms weak coordinate bond

Bond breaks when cell is reached

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28
Q

Why is CO toxic

A

Also bonds coordinately to Fe2+

Stops O2 from bonding

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29
Q

Why are transition metals coloured

A

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

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30
Q

How to calculate ΔE from f and / or λ

A

ΔE = hf = hc / λ

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31
Q

What affects colour of transition metal

A

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

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32
Q

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

A

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

33
Q

What is used to reduce vanadium

A

Zinc

34
Q

What colour is Fe2+ aqua ion

A

Green

35
Q

What colour is Fe3+ aqua ion

A

Pale brown

36
Q

What colour is Cr2+ aqua ion

A

Blue

37
Q

What colour is Cr3+ aqua ion

A

Red / violet

38
Q

What colour is Co2+ aqua ion

A

Brown

39
Q

What colour is Co3+ aqua ion

A

Yellow

40
Q

What does a colorimeter do

A

Measures absorbance of a particular wavelength of light by a solution

41
Q

How would you use colorimetry experimentally

A

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

42
Q

What information can a colorimeter provide

A

Concentration of a certain ion

43
Q

Why can transition metals have variable oxidation states

A

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

44
Q

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

A

+2 - Loss of electrons from 4s orbital

45
Q

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

A

No, they covalently bond to other species

46
Q

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

A

Tollen’s reagent to test for aldehydes / ketones

47
Q

What colour is MnO4-

A

Deep purple

48
Q

What colour is Mn2+

A

Pink

49
Q

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

A

Usually involve a colour change due to change in oxidation state

50
Q

What colour is Cr2O7 2-

A

Orange

51
Q

What colour is Cr3+

A

Green

52
Q

What happens to aqua metal ions in acidic conditions

A

They get reduced

53
Q

What happens to aqua metal ions in alkaline conditions

A

They get oxidised

54
Q

What happens to aqua metal ions in neutral conditions

A

No change

55
Q

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

A

E° values

56
Q

What can change these E° values

A

pH, ligands involved

57
Q

Define a catalyst

A

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

58
Q

How do catalysts work

A

Provide an alternative reaction pathway with a lower activation energy

59
Q

Why are transition metals good catalysts

A

Exist in variable oxidation states, easily provide alternative pathways

60
Q

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

A

Only exist in 1 oxidation state

61
Q

What are advantages of using a catalyst for a reaction

A

Allows reactions to proceed at lower temperatures and pressures

62
Q

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

A

Platinum, Rubidium, Palladium

Catalyse CO and NO to CO2 and N2

63
Q

Define heterogenous catalyst

A

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

64
Q

Advantage of using a heterogenous catalyst

A

No need for separation of products from catalyst

65
Q

How do heterogenous catalysts work

A

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

66
Q

What properties does the catalyst need to have

A

Can’t adsorb too strongly - no release

Can’t adsorb too weakly - no attachment

67
Q

How can you increase the efficiency of heterogeneous catalysts

A

Increase SA to increase number of active sites present

Also spread onto an inert support medium to increase surface area:mass ratio

68
Q

What is catalyst poisoning

A

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

69
Q

What effect does this have

A

Decreases effectiveness of catalyst over time

70
Q

How else can a catalyst be degraded

A

Finely divided catalysts can be gradually lost from their support medium

71
Q

What is in the Haber process

A

Makes ammonia from nitrogen and hydrogen

Fe catalyst

72
Q

Size and shape of catalyst for Haber process

A

Pea sized lumps to increase SA

73
Q

How long until catalyst is poisoned in Haber cycle

A

5 years - poisoned by sulfur impurities in gas stream

74
Q

What is the Contact process

A

Makes H2SO4 from SO2 and O2

Vanadium (V) oxide catalyst

75
Q

Why is V a good catalyst

A

Can change oxidation state

76
Q

Define homogenous catalyst

A

A catalyst in the same phase as the reactants

77
Q

How do they work

A

Form intermediates to give a reaction with lower activation energy

78
Q

Define autocatalysis

A

When a product of a reaction is also a catalyst

Chemistry (18 decks)

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