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Chemistry A Level 2023 > Transition Metals > Flashcards

Transition Metals Flashcards

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1
Q

Define a transition element

A

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

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2
Q

some characteristic physical properties of transition metals

A

metallic, good conductors of heat and electricity, hard, strong, shiny, high melting point, high boiling point, low reactivity

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3
Q

some uses of iron

A

vehicle bodies, to reinforce concrete

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4
Q

some uses of titanium

A

jet engine parts

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5
Q

some uses of copper

A

water pipes

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6
Q

what are the characteristic chemical properties of transition metals (there’s 4)

A

variable oxidation states (takes place in many redox reactions)
coloured compounds/ions in solution
good catalysts
form complex ions

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7
Q

define the term complex ion

A

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

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8
Q

transition metal catalyst in the Haber process

A

iron

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9
Q

transition metal catalyst in the contact process

A

vanadium (V) oxide

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10
Q

transition metal catalyst in the decomposition of H2O2

A

MnO2

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11
Q

which electrons do transition metals lose first when forming ions

A

4s

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12
Q

define ligand

A

an ion or molecule with at least one lone 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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13
Q

define monodentate ligands

A

forms one co-ordinate bond to central metal ion (one lone pair to donate)

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14
Q

define bidentate ligand

A

forms two co-ordinate bonds to central metal ion (two lone pairs to donate)

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15
Q

define multidentate ligand

A

forms 3+ co-ordinate bonds to central metal ion

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16
Q

4 common monodentate ligands

A

Cl-
H2O
NH3
CN-

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17
Q

what kind of ligand is ethanedioate

A

bidentate

-:O—C===O
I
-:O—C===O

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18
Q

what kind of ligand is benzene-1,2-diol

A

bidentate

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18
Q

what kind of ligand is benzene-1,2-diol

A

bidentate

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19
Q

what is the full name of en

A

ethane-1,2-diamine

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20
Q

what kind of ligand is en

A

bidentate

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21
Q

how many coordinate bonds does EDTA 4- form?

A

six

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22
Q

define the term coordination number

A

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

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23
Q

what is the chelate effect

A

chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule

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24
Q

explain the chelate effect in terms of entropy and the reaction that is occurring

A

number of molecules increases when multidentate ligands displace ligands that form fewer co-ordinate bonds per molecule
significant increase in entropy –> Gibbs’ free energy change <0 –> feasible reaction
a more stable complex ion is formed

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25
Q

what ion is usually formed when a transition metal compound is dissolved in water and what shape is it

A

aqua ion
6 H2O ligands around central metal ion
octahedral complex ion formed

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26
Q

if a transition metal ion has 2 ligands, what shape is it usually

A

linear

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27
Q

if a transition metal ion has 4 ligands, what shape is it usually

A

tetrahedral

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28
Q

name an exception to the general rule that ions with 4 ligands is generally tetrahedral. what shape is it?

A

platin is square planar (forms cisplatin)

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29
Q

what shape is a complex ion if it has 6 ligands

A

octahedral

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30
Q

what conditions are needed for a complex ion to display optical isomerism

A

usually applies to octahedral molecules with 2 or bidentate ligands, so that the mirror images are non-superimposable

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31
Q

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

A

decreases from 4 to 6 as Cl- is a much larger ligand than H2O and NH3

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32
Q

what is haem - its metal ion, coordination number and ligands

A

a molecule which makes up protein chains
Fe2+ central metal ion, which has a coordination number of 6
4 of these bonds are to ring system called porphyrin
1 is to the nitrogen of a globin (protein) molecule
1 is to an O2 molecule

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33
Q

how does haemoglobin transport oxygen

A

O2 forms a weak coordinate bond to the metal ion, then is transported around the body. the bond breaks when haemoglobin reaches cells and oxygen is released

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34
Q

why is CO toxic

A

CO also coordinately bonds to the Fe 2+, and is a better ligand, so bonds more strongly than O2
stops O2 from bonding to haemoglobin, so O2 cannot be transported around the body

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35
Q

why are transition metal compounds coloured

A
  • partially filled d-orbitals and electrons are able to move between the d-orbitals
  • in compounds, the d-orbitals split into different energy levels
  • electrons can absorb energy in the form of photons to become excited and move to a higher energy level (excited state)
  • energy of photon = energy different between levels
  • energy of photo is related to the frequency of light by E = hf
  • colour corresponding to the frequency of the energy change is missing from the spectrum, so we see a combination of all the colours that aren’t absorbed
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36
Q

how do you calculate ∆E from f and/or λ

A

∆E = hf = hc / λ

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37
Q

what affects the colour of a transition metal compound

A

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

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38
Q

VO2 + oxidation number and colour

A

5+
yellow

38
Q

VO 2+ oxidation number and colour

A

4+
blue

39
Q

V 3+ oxidation number and colour

A

3+
green

40
Q

V 2+ oxidation number and colour

A

2+
violet

41
Q

what can you use to reduce Vanadium

A

Zinc

42
Q

what colour is Fe 2+’s aqua ion

A

green

43
Q

what colour is Fe 3+’s aqua ion

A

pale brown

44
Q

what colour is Cr 2+’s aqua ion

A

blue

45
Q

what colour is Cr 3+’s aqua ion

A

red/violet

46
Q

what colour is Co 2+’s aqua ion

A

brown

47
Q

what colour is Co 3+’s aqua ion

A

yellow

48
Q

what does a colorimeter do

A

measures the absorbance of a particular wavelength of light by a solution

49
Q

how would you use colorimetry experimentally

A

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

50
Q

what information can a colorimeter give you

A

concentration of a certain ion in the solution

51
Q

why can transition metals have variable oxidation states

A

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

52
Q

which oxidation states do all transition metals have (except Sc) and why

A

+2 due to loss of electrons from 4s orbital

53
Q

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

A

no, after oxidation state of about III, metal ions covalently bond to other species

54
Q

what is the use of the complex [Ag(NH3)2]+ ion

A

tollens’ reagent to test for aldehydes/ketones (silver mirror formed with aldehyde, no visible change with ketone)

55
Q

what colour is MnO4-

A

deep purple

56
Q

what colour is Mn 2+

A

pink

57
Q

write half equation for the reduction of MnO4 - to Mn 2+

A

MnO4 - + 8H+ + 5e- —> Mn2+ + 4H2O

58
Q

why are redox titration with transition metal compounds said to be self-indicating

A

they usually involve a colour change as the metal is changing oxidation state; sometimes an indicator is still needed/useful

59
Q

what colour is Cr2O7 2-

A

orange

60
Q

what colour is Cr 3+

A

green

61
Q

write a half equation for the reduction of Cr2O7 2- to Cr 3+

A

CrO7 2- + 14H+ + 6e- —-> 2Cr 3+ + 7H2O

62
Q

what happens to aqua metal ions in acidic conditions

A

they get reduced

63
Q

what happens to aqua metal ions in alkaline conditions

A

they get oxidised

64
Q

what happens to aqua metal ions in neutral conditions

A

no change

65
Q

what decides whether reduction/oxidation occurs and the readiness of the reaction depend on

A

E values

66
Q

what can change E values

A

pH and ligands involved

67
Q

define a catalyst

A

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

68
Q

how do catalysts usually work

A

provide an alternative reaction pathway with a lower activation energy

69
Q

why are transition metals good catalysts

A

they can exist in variable oxidation states, so can provide alternative pathways easily

70
Q

why are group 1, 2 and 3 metals not as good catalysts

A

only exist in one oxidation state

71
Q

what are advantages of using a catalyst for a reaction

A

allows reactions to proceed at lower temperature and pressure –> save valuable energy and resources

72
Q

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

A

Pt, Rd, Pd

CO, NO –> CO2, N2 and CxH(2x+2) –> H2O, CO2

73
Q

define a heterogeneous catalyst

A

catalysyt 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

74
Q

what is an advantage of using a heterogeneous catalyst

A

no need for separation of products from catalyst

75
Q

how do heterogeneous catalysts work

A

reactants adsorb to the catalysts’ surface at active sites. this weakens bonds within the reactants, holds reactants close together on the surface and/or in the correct orientation to react. once the reaction has occurred, products desorb from the active sites

76
Q

what properties does the catalyst need to have to make it a good catalyst

A

can’t adsorb too strongly, otherwise the products will not desorb
can’t adsorb too weakly as reactant would not be held in place for long enough and bonds would not be sufficiently weakened
need a good balance between desorption and adsorption

77
Q

how can you increase the efficiency of heterogeneous catalysts

A
  • increase the surface area to increase the number of active sites that are present
  • also spread onto an inert support medium, e.g. ceramic, to increase the surface/mass ratio. use ceramic honeycomb matrix/mesh/sponge
78
Q

what is catalyst poisoning

A

unwanted impurities adsorb to the catalysts’ active sites and do not desorb
this blocks the active sites on the catalyst’s surface

79
Q

what effect does catalyst poisoning have on catalytic activity

A

decreases the effectiveness of the catalyst over time

80
Q

how else can a catalyst be degraded aside from catalyst poisoning

A

finely divided catalysts can be gradually lost from their support medium

81
Q

what is the Haber process and what catalyst is used

A

N2 (g) + 3H2 (g) –> 2NH3 (g)
makes ammonia
uses iron (Fe) catalyst

82
Q

what size/shape is the catalyst for the Haber process

A

pea sized lumps to increase surface area

83
Q

how long does the catalyst last for the Haber process? what is it poisoned by?

A

approx 5 years
poisoned by sulfur impurities in the gas streams

84
Q

what is the contact process? what is the catalyst ?

A

makes H2SO4 -
catalysed by vanadium (V) oxide V2O5
2SO2 (g) + O2 (g) —> 2SO3 (g)

85
Q

what are the two reactions that are involved in the contact process

A

SO2 + V2O5 —> SO3 + V2O4
V2O4 + 1/2 O2 —> V2O5

86
Q

why is V a good catalyst in the case of the contact process

A

can change oxidation state from 5+ to 4+ and back to 5+ (so it can be used again)

87
Q

define homogeneous catalyst

A

catalyst that is in the same phase as the reactants

88
Q

how do homogeneous catalysts work

A

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

89
Q

what is the reaction between S2O8 2- ions and I- ions

A

S2O8 2- + 2I- —> 2SO4 2- + I2 (all aq)

90
Q

why does the reaction between S2O8 2- ions and I- ions have a higher activation energy in normal conditions

A

two negative ions are reacting
they repel each other so activation energy is high

91
Q

which transition metal ions catalyse the reaction between S2O8 2- and I- ions?
give 2 reactions that do

A

Fe 2+
S2O8 2- + 2Fe 2+ —> 2Fe 3+ + 2SO4 2-
2Fe 3+ + 2I - —> 2Fe 2+ + I2

92
Q

define the term autocatalysis

A

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

93
Q

concentration of reactant against time graph for autocatalysed reactuon

A
  • initially slow, uncatalysed as not much of catalyst has been formed
  • rate increases as catalyst is made; catalysed reaction is faster
  • slows down as reactants are used up
94
Q

write a half equation for the conversion of C2O4 2- ions into CO2

A

C2O4 2- —-> 2CO2 + 2e-

95
Q

write an equation for the reaction between Cr2O4 2- ions and MnO4 - ions
how does Mn 2+ autocatalyse this reaction

A

2MnO4 - + 16H+ + 5C2O4 2- —-> 10CO2 + 2Mn 2+ + 8H2O

1st stage
MnO4 - + 4Mn 2+ + 8H+ —> 4H2O + 5Mn 3+
2nd stage
2Mn 3+ + C2O4 2- —> 2CO2 + 2Mn 2+

Chemistry A Level 2023 (8 decks)

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