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Inorganic Chemistry > 3.2.5 Transition metals (A2) > Flashcards

3.2.5 Transition metals (A2) Flashcards

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

where are transition metals located in the periodic table?

A

the middle - part of the d block

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3
Q

what are some characteristic 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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4
Q

what are some uses of iron?

A

vehicle bodies, to reinforce concrete

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5
Q

what is a use of titanium?

A

jet engine parts

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6
Q

what is a use of copper?

A

water pipes

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7
Q

what are the characteristic chemical properties of transition metals?

A

variable oxidation states
coloured compounds/ions
good catalysts
form complex ions

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8
Q

define the term complex ion.

A

central transition metal ion surrounded by ligands (other ions/molecules) that are co-ordinately bonded to it

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9
Q

give some examples of transition metal catalysts and the processes/reactions they catalyse.

A

iron - haber process
vanadium oxide - contact process
MnO2 - decomposition of H2O2

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10
Q

which electrons do transition metals lose first when forming ions?

A

4s

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11
Q

define the term ligand.

A

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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12
Q

define the term mono/unidentate ligands?

A

a ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)

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13
Q

define the term bidentate ligand.

A

a ligand that forms two co-ordinate bonds to the central metal ion (2 lone pairs to donate)

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14
Q

define the term multidentate ligand.

A

a ligand that forms three or more co-ordinate bonds to the central metal ion.

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15
Q

give some examples of common monodentate ligands.

A

Cl-, H2O, NH3, CN-

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16
Q

how many co ordinate bonds are in ethanedioate?

A

2 co-ordinate bonds

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17
Q

how many coordinate bonds are in benzene-1,2-diol?

A

2 coordinate bonds

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18
Q

how many coordinate bonds are in ethane-1,2-diamine?

A

2 coordinate bonds

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19
Q

how many coordinate bonds does EDTA4- form?

A

six

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20
Q

define the term coordination number.

A

number of coordinate bonds the metal ion has formed to surrounding ligands

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21
Q

what is the chelate effect?

A

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

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22
Q

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

A

number of molecules increases when multidentate ligands, eg. EDTA, displace ligands that form fewer coordinate bonds per molecule
significant increase in entropy - gibbs free energy change is less than zero - feasible reaction
a more stable complex ion is formed

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23
Q

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

A

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

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24
Q

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

A

linear

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25
Q

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

A

tetrahedral

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26
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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27
Q

what shape is a complex ion if it has 6 ligands?

A

octahedral

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28
Q

how can complex ions display E/Z or cis-trans isomerism? what shapes of ion does this apply to?

A

ligands differ in the way in which they are arranged in space
2 ligands of the same type can be on the same side of the metal ion (forming E or cis isomer) or opposite sides of the metal ion (forms the Z or trans isomer)
applies to square planar and octahedral complex ions.

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29
Q

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

A

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

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30
Q

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

A

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

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31
Q

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

A

molecule which makes up protein chains
Fe2+ central ion
coordination number of 6
4 of the bonds are to a ring system called porphyrin, 1 to the nitrogen of a globin molecule, one to an oxygen in an O2 molecule

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32
Q

how does haemoglobin transport oxygen?

A

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

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33
Q

why is CO toxic?

A

CO also co-ordinately bonds to the Fe2+ and is a better ligand, bonds more strongly than O2.
stops O2 from bonding to haemoglobin, so O2 cannot be transported around the body.

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34
Q

why are transition metal compounds coloured?

A

they have partially filled d-orbitals and electrons are able to move between the d-orbitals.
in compounds (where ligands are co-ordinately bonded) the d-orbitals split into different energy levels.
electrons can absorb energy in order to become “excited” and move to a higher energy level.
the 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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35
Q

how do you calculate delta E from f and/or λ?

A

delta E=hf=hc/λ

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36
Q

what affects the colour of a transition metal compound?

A

coordination number
shape
oxidation state of metal
number and type of ligands

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37
Q

what can be used to reduce vanadium?

A

zinc

38
Q

what colour is Fe2+’s aqua ion?

A

green

39
Q

what colour is Fe3+’s aqua ion?

A

pale brown

40
Q

what colour is Cr2+’s aqua ion?

A

blue

41
Q

what colour is Cr3+’s aqua ion?

A

red/violet

42
Q

what colour is Co2+’s aqua ion?

A

brown

43
Q

what colour is Co3+’s aqua ion?

A

yellow

44
Q

what does a colourimeter do?

A

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

45
Q

how would you use colourimetry experimentally?

A

use solutions of known concentration to create a calibration curve: find unknown concentration

46
Q

what information can a colourimeter give you?

A

the concentration of a certain ion in the solution

47
Q

why can transition metals have variable oxidation states?

A

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

48
Q

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

A

+2 due to loss of electrons from 4s orbital.

49
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

50
Q

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

A

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

51
Q

what colour is MnO4-?

A

deep purple

52
Q

what colour is Mn2+?

A

pink

53
Q

why are redox titrations 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

54
Q

what colour is (Cr2O7)2-?

A

orange

55
Q

what colour is Cr3+?

A

green

56
Q

write a half equation for the reduction of MnO4- to Mn2+.

A

MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

57
Q

write a half equation for the reduction of (Cr2O7)2- to Cr3+

A

(Cr2O7)2- + 14H+ + 6e- –> 2Cr3+ + 7H2O

58
Q

what happens to aqua metal ions in acidic conditions?

A

they get reduced

59
Q

what happens to aqua metal ions in alkaline conditions?

A

they get oxidised

60
Q

what happens to aqua metal ions in neutral conditions?

A

no change

61
Q

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

A

E values

62
Q

what can change these E values?

A

pH, ligands involved

63
Q

define a catalyst.

A

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

64
Q

How do catalysts usually work?

A

Provide an alternative reaction pathway with a lower activation energy.

65
Q

Why are transition metals good catalysts?

A

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

66
Q

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

A

Only exist in one oxidation state

67
Q

What are advantages of using a catalyst for a reaction?

A

Allows reactions to proceed at lower temperatures and pressures —> saves valuable energy and resources

68
Q

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

A

Pt, Rd, Pd
Catalyse CO, NO —> CO2, N2 and CnH2n+2 —> H2O, CO2

68
Q

Define a heterogeneous catalyst.

A

Catalyst which is present in the reaction in a different phase to the reactants (usually a solid, with liquid or gas reactants)
Catalytic activity occurs on the solid surface as the reactants pass over it

69
Q

What is the advantage of using a heterogeneous catalyst?

A

No need for separation of products from catalyst

70
Q

How do heterogeneous catalysts work?

A

Reactants absorb to the heterogeneous catalyst’s 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 reaction has occurred, products desorb from the active sites

71
Q

What properties do catalysts need to be a good catalyst?

A

Can’t adsorb too strongly, otherwise 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.

72
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, eg. Ceramic, to increase the surface/mass ratio. Use ceramic honeycomb matrix/mesh/sponge

73
Q

What is catalyst poisoning?

A

Unwanted impurities adsorb to the catalyst’s active site and do not desorb.
This blocks the active sites on the catalyst’s surface

74
Q

What effect does catalyst poisoning have on a catalytic activity?

A

Decreases the effectiveness of the catalyst over time

75
Q

How else, other than catalyst poisoning, can a catalyst be degraded?

A

Finely divided catalysts can be gradually lost from their support medium

76
Q

What is the Haber process? What catalyst is used?

A

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

77
Q

What size/shape if the catalyst for the Haber process?

A

Pea sized lumps to increase surface area

78
Q

How long does the catalyst last for the Haber process? What is it poisoned by?

A

About 5 years
Poisoned by sulphur impurities in the gas streams

79
Q

What is the Contact process? What is the catalyst?

A

Makes H2SO4. Catalysed by vanadium oxide - V2O5
2SO2(g) + O2(g) —> 2SO3(g)

80
Q

What are the two reactions that are involved in the contact process?

A

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

80
Q

Why is V a good catalyst in the case of the Contact process?

A

Can change oxidation state from 5+ to 4+ and then back to 5+ (So can be used again)

81
Q

Define a homogeneous catalyst.

A

A catalyst that is in the same phase

82
Q

How do homogeneous catalysts work?

A

Form intermediates to give a different reaction pathway with a lower Ea

83
Q

What is the reaction between (S2O8)2- ions and I- ions?

A

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

84
Q

Why does the reaction between (S2O8)2- ions and I- ions have a high Ea in normal conditions?

A

Two negative ions are reacting
They repel each other so Ea is high

85
Q

Which transition metal ions catalyse the reaction between (S2O8)2- ions and I- ions? Write two equations to show how.

A

Fe2+
(S2O8)2- + 2(Fe)2+ —> 2(Fe)3+ + 2(SO4)2-
2(Fe)3+ + 2I- —> 2(Fe)2+ + I2

86
Q

Define the term autocatalysis.

A

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

87
Q

Write a half equation for the conversion of (Cr2O4)2- ions into CO2.

A

(Cr2O4)2- —> 2CO2 + 2e-

88
Q

Write an equation for the reaction between (C2O4)2- ions and (MnO4)- ions. How does Mn2+ autocatalyse this reaction?

A

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

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

89
Q

How can you monitor the concentration of (MnO4)- ions?

A

Using a colourimeter

Inorganic Chemistry (6 decks)

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