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Chemistry revision > Transition Metals > Flashcards

Transition Metals 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 the transition metals located in the periodic table?

A

In the middle (block from Ti to Cu) - 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 m.p., high b.p., low reactivity.

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4
Q

Some uses of iron?

A

Vehicle bodies, to reinforce concrete

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5
Q

Some uses of titanium?

A

Jet engine parts

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6
Q

Some uses of copper?

A

Water pipes

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7
Q 
What are the characteristic chemical properties of
transition metals (4)?
A

Variable oxidation states → take part in many redox reactions
Coloured compounds/ions in solution
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-ordinated bonded to it.

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9
Q

Give some example of transition metals catalysts and the processes/reactions they catalyse (3)?

A

Iron - Haber process
Vanadium (V) 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

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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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 (4).

A

Cl-, H2O, NH3, CN-

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16
Q

How many co-ordinate bonds can ethanedioate form to a transition metal ion?

A

2 co-ordinate bonds

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17
Q

How many co-ordinate bonds can benzene-1,2-diol form to a transition metal ion?

A

2 co-ordinate bonds

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18
Q

How many co-ordinate bonds can ethane-1,2-diamine form to a transition metal ion?

A

2 co-ordinate bonds

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19
Q

How many co-ordinate bonds does EDTA4- form?

A

6

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20
Q

What is the shortened

name of ethane-1,2-diamine?

A

en

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21
Q

Define the term coordination number

A

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

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22
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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23
Q

Explain the Chelate effect in terms of entropy and the reaction that is occurring

A

Number of molecules increases when multidentate ligands,
e.g. EDTA, 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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24
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 is formed

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25
Q

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

A

Linear

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26
Q

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

A

Tetrahedral

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27
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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28
Q

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

A

Octahedral

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29
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 (next to each
other), which forms the E or cis isomer
-2 ligands of the same type can be on opposite sides of the metal ion (not next to
each other), which forms the Z or trans isomer
Applies to square planar and octahedral complex ions

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30
Q

What conditions are needed for a complex ion display to 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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31
Q

What happens to Co2+, Cu2+ and Fe3+ ‘s 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, with an Fe2+
central metal ion, which has a coordination number of 6.
4 of these bonds are to a ring system called porphyrin. 1 is to the nitrogen of a globin (protein) molecule and one is to an oxygen in 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 Fe2+, 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
  • They have partially filled d-orbitals and electrons are able to move between the d-orbitals.
  • In compounds (when ligands coordinately bond to the ion), the d-orbitals split into different energy levels.
  • Electrons can absorb energy in the form of photons to become excited to a higher energy level
  • Energy of photon = energy difference between levels
  • Energy of photon is related to frequency of light by E =hf
  • 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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36
Q

How do you calculate ΔE from f and/or λ?

A

ΔE=hf=hc÷λ

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37
Q

What affects the colour of a transition metal compound?

A

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

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38
Q

What is the oxidation number and colour for VO2^+?

A

Oxidation number: 5+

Colour: Yellow

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39
Q

What is the oxidation number and colour for VO^2+?

A

Oxidation number: 4+

Colour: Blue

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40
Q

What is the oxidation number and colour for V^3+?

A

Oxidation number: 3+

Colour: Green

41
Q

What is the oxidation number and colour for V^2+?

A

Oxidation number: 2+

Colour: Violet

42
Q

What can you use to reduce Vanadium?

A

Zinc

43
Q

What colour is Fe2+’s aqua ion?

A

Green

44
Q

What colour is Fe3+’s aqua

ion?

A

Pale brown

45
Q

What colour is Cr2+’s aqua ion?

A

blue

46
Q

What colour is Cr3+’s aqua ion?

A

red/violet

47
Q

What colour is Co2+’s aqua ion?

A

Brown

48
Q

What colour is Co3+’s aqua ion?

A

Yellow

49
Q

What does a colorimeter do?

A

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

50
Q

How would you use colorimetry experimentally?

A

Use solutions of known concentration to create a

calibration graph; find unknown concentration

51
Q

What information can a colorimeter give you?

A

The concentration of a certain ion in the solution

52
Q

Why can transition metals have variable oxidation states?

A

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

53
Q

Which oxidation states do all transition metals have

(except Sc)? Why?

A

+2 due to loss of electrons from 4s orbital

54
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

55
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)

56
Q

What colour is MnO4-?

A

Deep purple

57
Q

What colour is Mn2+?

A

Pink

58
Q

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

A

MnO4- +8H+ +5e- → Mn2+ +4H2O

59
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

60
Q

What colour is Cr2O72-?

A

Orange

61
Q

What colour is Cr3+?

A

Green

62
Q

Write a half equation for the reduction of Cr2O72- to Cr3+

A

Cr2O72- + 14H+ +6e- → 2Cr3+ +7H2O

63
Q

What happens to aqua metal ions in acidic conditions?

A

They get reduced

64
Q

What happens to aqua metal ions in alkaline conditions?

A

They get oxidised

65
Q

What happens to aqua metal ions in neutral conditions?

A

No change

66
Q

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

A

E° values

67
Q

What can change these E° values?

A

pH, ligands involved

68
Q

Define a catalyst

A

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

69
Q

How do catalysts usually work?

A

Provide an alternative reaction pathway with a

lower activation energy

70
Q

Why are transition metals good catalysts?

A

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

71
Q

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

A

Only exist in one oxidation state

72
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

73
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 CxH2x+2 →H2O, CO2

74
Q

Define a heterogeneous catalyst

A

A catalyst that is present in the reaction in a different phase to the reactants (usually a solid,
with gas/liquid reactants).
Catalytic activity occurs on the solid surface as the reactants pass over it

75
Q

What is an advantage of using a heterogeneous

catalyst?

A

No need for separation of products from catalyst

76
Q

How do heterogeneous catalysts work?

A
  1. Reactants adsorb to the catalyst’s surface at active sites.
    2.This weakens bonds within the reactants, holds reactants close together on the surface and/or in the correct orientation to
    react.
  2. Once the reaction has occurred, products desorb from the active sites.
77
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.
78
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.
79
Q

What is catalyst poisoning?

A

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

80
Q

What effect does catalyst poisoning have on catalytic

activity?

A

Decreases the effectiveness of the catalyst over time

81
Q

How else can a catalyst be degraded?

A

Finely divided catalysts can be gradually lost from their support medium

82
Q

What is the Haber process? What catalyst is used?

A

N2 (g) + 3H2 (g) → 2NH3 (g) Makes ammonia

83
Q

What catalyst is used during the Haber process?

A

Uses iron (Fe) catalyst

84
Q

What size/shape is the catalyst for the Haber

process?

A

Pea sized lumps to increase surface area

85
Q

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

A

About 5 years.

Poisoned by sulfur impurities in the gas streams

86
Q

What is the Contact Process?

A

Makes H2SO4

2SO2 (g) + O2 (g) → 2SO3 (g)

87
Q

What is the catalyst in the contact process?

A

Catalysed by vanadium (V) oxide- V2O5

88
Q

What are the two reactions that are involved in the

contact process?

A

SO2 + V2O5 → SO3 + V2O4

V2O4 + ½O2 → V2O5

89
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 can be used again)

90
Q

Define homogeneous catalyst

A

A catalyst that is in the same phase as the reactants.

91
Q

How do homogeneous catalysts work?

A

Form intermediates to give a different reaction pathway with lower EA

92
Q

What is the reaction between S2O82- ions and I- ions?

A

S2O82- + 2I- → 2SO42- + I2 (all aq)

93
Q

Why does the reaction between S2O82- 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

94
Q

Which transition metal ions catalyse the reaction between S2O82- ions and I- ions? Write 2 equations to show how

A

Fe2+
S2O82- + 2Fe2+ → 2Fe3+ + 2SO42-
2Fe3+ + 2I- → 2Fe2+ + I2

95
Q

Define the term autocatalysis

A

When the product of a reaction is also a catalyst

for that reaction.

96
Q

Write a half equation for the conversion of C2O42- ions into CO2

A

C2O42- → 2CO2 + 2e-

97
Q

Write an equation for the reaction between C2O42- ions and MnO4- ions. How does Mn2+ autocatalyse
this reaction?

A

2MnO4- + 16H+ + 5C2O42- → 10CO2 + 2Mn2+ + 8H2O
1st stage: MnO4- + 4Mn2+ + 8H+ → 4H2O + 5Mn3+
2nd stage: 2Mn3+ + C2O42- → 2CO2 + 2Mn2+

98
Q

How can you monitor the concentration of MnO4- ions?

A

Using a colorimeter

Chemistry revision (46 decks)

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