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Chemistry A - Level > Topic 15 (Part 2) - Principles of Transition Metal Chemistry > Flashcards

Topic 15 (Part 2) - Principles of Transition Metal Chemistry Flashcards

Vanadium Compounds, Chromium Compounds and Catalysts

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1
Q

What is the transition metal that is in the centre of the haemoglobin complex?

A

Fe (II)

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2
Q

What happens when someone breathes in CO?

A

A ligand exchange reaction - the CO ligand is a stronger ligand than O2 molecules, therefore, when someone breathes in CO it displaces the O2 molecules from the Fe (II) complex. This reaction is irreversible which is why less oxygen can now be transported around the body.

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3
Q

How many oxidation states does Vanadium have? What are they?

A

4:
- +2
- +3
- +4
- +5

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4
Q

What colour is the compound VO2(+) in solution? What is the oxidation state of vanadium in this compound?

A

Yellow, +5

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5
Q

What colour is the compound VO(2+) in solution? What is the oxidation state of vanadium in this compound?

A

Blue, +4

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6
Q

What colour is the compound V(3+) in solution? What is the oxidation state of vanadium in this compound?

A

Green, +3

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7
Q

What colour is the compound V(2+) in solution? What is the oxidation state of vanadium in this compound?

A

Violet, +2

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8
Q

What is observed as VO2(+) is reduced to VO(2+)?

A

A green coloured solution as some VO2(+) ions are present (yellow) and some VO(2+) ions are present (blue) - there is a mixture so we observe a green colour

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9
Q

What value of Ecell means that a reaction is theoretically feasible?

A

Ecell > 0

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10
Q

What value of Ecell means that a reaction is theoretically likely to go to completion?

A

Ecell > 0.6

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11
Q

Even if a reaction is theoretically feasible, why might it not happen in practice?

A

As the reaction is not kinetically feasible at RT and has a high activation energy

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12
Q

In what conditions can vanadium be reduced from its +5 oxidation state to its +2 oxidation state?

A

With zinc in acidic conditions

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13
Q

Balance the equation for the reduction of VO2(+) to VO(2+) with state symbols

A

VO2(+) (aq) + 2H+ (aq) + e- <-> VO(2+) (aq) + H2O (l)

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14
Q

Why is the final reduction step of vanadium from V(3+) to V(2+) often quite difficult to observe?

A

The Ecell value for this reduction is negative (meaning the oxidation is favourable). Therefore, the reduction requires high temperatures to occur.

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15
Q

What is the equation for Gibbs Free energy that includes Ecell values?

A

-nFEcell

n - number of electrons involved in the redox reaction
F - Faradays constant

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16
Q

How many stable oxidation states does Cr have? What are they?

A

3:
+2
+3
+6

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17
Q

What is the colour of the Cr2O7(2-) ion in solution? What is the oxidation state of chromium in this compound?

A

orange, +6

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18
Q

What is the name of the Cr2O7(-) ion?

A

dichromate (VI) ion

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19
Q

What is the colour of the Cr(3+) ion in solution? What is the oxidation state of chromium in this compound?

A

green, +3

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20
Q

What is the colour of the Cr(2+) ion in solution? What is the oxidation state of chromium in this compound?

A

blue, +2

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21
Q

Balance the equation for the reduction of Cr2O7(2-) to Cr(3+)

A

Cr2O7(2-) + 6e- +14H+ -> 2Cr(3+) + 7H2O

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22
Q

What is the amphoteric complex that you need to know?

A

[Cr(H2O)3(OH)3]

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23
Q

In what conditions can chromium be reduced from its +6 oxidation state to its +2 oxidation state?

A

With zinc in acidic conditions

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24
Q

Write the reversible reaction equation to form dichromate ions from chromate ions?

A

2CrO4(-) + 2H+ <-> Cr2O7(2-) + H2O

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25
Q

What oxidation state is chromium in chromate ions?

A

+6

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26
Q

Write the formula of chromate ions?

A

CrO4(2-)

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27
Q

What conditions are required in the oxidation of Cr (3+) to CrO4(2-)?

A

alkaline

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28
Q

What is the oxidising agent in the oxidation of Cr (3+) to CrO4(2-)?

A

H2O2, hydrogen peroxide

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29
Q

What process is required to form dichromate ions from chromate ions?

A

Acidification

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30
Q

What is the colour change when chromate ions are acidified to form dichromate ions?

A

yellow solution to orange solution

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31
Q

Why do the chromate ions need to be in acidic conditions to form dichromate ions?

A

The acidic conditions causes the position of equilibrium to shift to the right in order to reverse the change. This causes an increase in the concentration of Cr2O7 that you produce (this is why you produce acidified K2Cr2O7)

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32
Q

Write the equation showing the oxidation of Cr(3+) to Cr(6+)

A

Cr(OH)6 + (H2O2) -> CrO4(2-)

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33
Q

Write the equation showing the reduction of Cr(6+) to Cr(3+)

A

Cr2O7(2-) (alcohol e.g ethanol) -> Cr(H2O)6

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34
Q

What is the reducing agent in the reduction of Cr(6+) to Cr(3+)?

A

Ethanol, any alcohol

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35
Q

Write the equation showing the oxidation of Cr(2+) to Cr(3+)

A

Cr(H2O)6 + (HNO3) -> Cr(H2O)6

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36
Q

What is the oxidising agent in the oxidation of Cr(2+) to Cr(3+)?

A

Conc. HNO3 (acidic)

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37
Q

What is the observed colour change in the oxidation of Cr(2+) to Cr(3+)?

A

blue to green

38
Q

What is the observed colour change in the reduction of Cr(6+) to Cr(3+)?

A

orange to green

39
Q

Which types of ligands will form the most stable complex ions?

A

MOST -> LEAST
hexadentate/multidentate , bidentate, monodentate

40
Q

What shows that the substitution of a monodentate ligand by a multidentate ligand is favourable and forms a much more stable complex?

A

The large positive increase in (delta)S of the system

41
Q

In terms of entropy what is favoured more, order or disorder?

A

disorder

42
Q

Write an equation to show how the Cr precipitate behaves as an alkali?

A

[Cr(H2O)3(OH)3] + 3H+ <-> Cr(H2O)6

43
Q

Why are transition metals good catalysts?

A

As they have variable oxidation states - this means that they can catalyse redox reactions by acting as both oxidising reagents and reducing reagents in the same time

44
Q

What is the definition of a catalyst?

A

A substance which speeds up the rate of reaction without being used up. It provides an alternate pathway with a lower activation energy so a greater proportion of molecules have the required Ea in order to react.

45
Q

Does using a catalyst affect the position of equilibrium?

A

No - but allows the equilibrium to be reached quicker

46
Q

What is the definition of a heterogenous catalyst?

A

Catalysts that are in a different phase/state to the species in the reaction

47
Q

What is the definition of a homogenous catalyst?

A

Catalysts that are in the same phase/state to the species in the reaction

48
Q

Can transition metals and their compounds act as catalysts?

A

Yes

49
Q

Where does the reaction occur when a heterogenous catalyst is being used?

A

On the surface of the catalyst

50
Q

What is the contact process?

A

The production of sulphur trioxide from sulphur dioxide (further reactions to produce sulphuric acid)

51
Q

What catalyst is used in the contact process?

A

V2O5, Vanadium oxide

52
Q

What type of catalyst is the catalyst used in the contact process?

A

A heterogenous catalyst

53
Q

What are the conditions for the contact process?

A
  • 450 degrees C
  • 1-2 atm
54
Q

What is the overall equation for the production of SO3 from SO2 in the contact process?

A

2SO2 + O2 (V2O5) <-> 2SO3

55
Q

What are the intermediate steps for the production of SO3 from SO2 in the contact process?

A

SO3 formed
SO2 + V2O5 -> V2O4 + SO3

Catalyst reformed
V2O4 + 1/2O2 -> V2O5

56
Q

What is the equation for producing sulphur dioxide for the contact process?

A

S (g) + O2 (g) -> SO2

  • burning sulphur in air
57
Q

In terms of oxidation number, how does vanadium oxide act as a catalyst in the contact process?

A

The vanadium in V2O5 is initially reduced from a +5 oxidation state to a +4 oxidation state. It is then reformed/oxidised back to its original oxidation state.

58
Q

What factors affect the yield of SO3 in the production of SO3 from SO2 in the contact process? Why?

A

Temperature - The reaction is exothermic, therefore low temperatures would be preferred in order to shift the position of equilibrium to the right. However, the reaction requires high temperatures to happen, therefore 450 degrees C acts as a compromise between a fast rate and high yield.

Pressure - There are three gaseous molecules on the LHS of the reaction and only 2 on the RHS, therefore, to increase the yield of SO3 you would want to do this reaction in high pressures. However, this reaction is normally done at around room pressure as the yield is already very high therefore it would not be economically beneficial to put money into creating higher pressures for such a small increase in yield.

59
Q

What is the main use of catalytic converters?

A

To remove poisonous chemicals from the car exhaust

60
Q

What is the catalyst used in catalytic converters?

A

Expensive metals:
- palladium
- platinum
- rhodium

61
Q

What type of catalyst is used in catalytic converters?

A

A heterogenous catalyst

62
Q

Write an equation for a reaction that occurs on the surface of the catalyst in catalytic converters

A

2CO (g) + 2NO (g) -> 2CO2 (g) + N2 (g)

63
Q

Describe the method of action of the catalyst in catalytic converters

A
  • First the CO and NO molecules are adsorbed onto the surface of the catalyst
  • Then the bonds in the CO and NO molecules are weakened causing them to react together to form the safe CO2 and N2
  • The products are then desorbed from the surface of the catalyst
64
Q

What are the two ways that cost can be minimised and efficiency can be maximised in catalytic converters?

A
  • Increasing the SA of the catalyst
  • Coating an inert surface medium with the catalyst to avoid using up large amounts of it

This is done by coating a honeycomb like structure with the catalyst

65
Q

How does a homogenous catalyst affect the reaction profile of a reaction?

A

For an exothermic reaction for example:
- Your reactants begin at a high energy level
- You produce an intermediate of a higher energy level
- You then produce products of lower energy levels

66
Q

How does a heterogenous catalyst affect the reaction profile of a reaction?

A

For an exothermic reaction for example:
- Your reactants begin at a high energy level
- You then produce products of lower energy levels

NO INTERMEDIATE

67
Q

What transition metal ion is used as the catalyst for the reaction between I-, iodide ions, and S2O8(2-) peroxodisulfate ions?

A

Fe (2+)

68
Q

Write the overall equation for the reaction between iodide ions and

A

2I (-) + S2O8 (2-) -> 2SO4 (2-) + I2

69
Q

Write the first equation in the reaction between I-, iodide ions, and S2O8(2-) peroxodisulfate ions? What are the oxidation states of the catalyst before and after?

A

2Fe (2+) + S2O8 (2-) -> 2Fe (3+) + 2SO4 (2-)

Fe:
+2 -> +3

S:
+7 -> +6

70
Q

Write the second equation in the reaction between I-, iodide ions, and S2O8(2-) peroxodisulfate ions? What are the oxidation states of the catalyst before and after?

A

2Fe (3+) + 2I (-) -> I2 + 2Fe (2+)

Fe:
+3 -> +2

I:
-1 -> 0

71
Q

How doe Fe (2+) act as a catalyst in the reaction between I-, iodide ions, and S2O8(2-) peroxodisulfate ions?

A
  • The iron first reduces the peroxodisulfate ions, it itself being oxidised.
  • Then the iron oxidises the Iodide ions, it itself being reduced back to its original form Fe (2+).
  • The Fe (2+) can then go on to reduce more peroxodisulfate ions.
72
Q

What is the definition of autocatalysis?

A

A term used to describe when one of the products of a reaction acts as a catalyst for it, thereby speeding it up

73
Q

What does a graph of concentration of products versus time look for an autocatalysis reaction?

A

Initially the rate of reaction is quite slow, therefore, the conc. of the reactant decreases slowly. However, once you have started producing more and more product, hence catalyst, the rate of reaction increases dramatically therefore the concentration of reactant also decreases rapidly. The graph finally levels off as the concentration of reactant plateaus to 0.

74
Q

What is the example of an autocatalysed reaction that you need to know?

A

Manganate (VII) ions, MnO4(-) + Oxalate/Ethandioate, C2O4(2-), ions

75
Q

Write the half equation for C2O4(2-) in the autocatalysis reaction you need to know

A

C2O4(2-) (aq) -> 2CO2 (g) + 2e-

76
Q

Write the half equation for MnO4(-) in the autocatalysis reaction you need to know

A

MnO4(-) + 5e- + 8H+ -> Mn(2+) + 4H2O

77
Q

Write the full equation for the autocatalysis reaction you need to know

A

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

78
Q

What is the catalyst for the autocatalysis reaction you need to know?

A

Mn (2+) - produced as a product in the reaction

79
Q

Write the two equations that show MN (2+) acting as a catalyst once it has been produced in the autocatalysis reaction you need to know

A

4Mn2+ (aq) + MnO4– (aq) + 8H+ (aq) → 5Mn3+ (aq) + 4H2O (aq)

2Mn3+ (aq) + C2O42- (aq) → 2CO2 (g) + 2Mn2+ (aq)

80
Q

What type of ligand is EDTA(4-)?

A

hexadentate

81
Q

What type of ligand is oxalate, C2O4 (2-) (ox)?

A

Bidentate

82
Q

What type of ligand is 1,2 - diaminoethane (en)?

A

Bidentate

83
Q

What type of ligand is H2O?

A

Monodentate

84
Q

What type of ligand is Cl-?

A

Monodentate

85
Q

Write the ligands: (en) , (ox)2- , EDTA(4-) , H2O and Cl- in order of most stable to least stable ligand (therefore which ones will displace which)

A

MOST STABLE
- EDTA (4-)
- Ox (2-)
- En
- H2O/Cl-

86
Q

How do the displacement equations of different types of ligand show their different stabilities?

A

How disordered each side of the equation is

87
Q

Write the displacement reaction of the copper - (en) complex with EDTA (4-)

A

Cu(en)2 + EDTA(4-) <=> Cu(EDTA) + 2(en)

88
Q

Write the displacement reaction of the copper - (ox) complex with EDTA (4-)

A

Cu(ox)2 + EDTA(4-) <=> Cu(EDTA) + 2(ox)(2-)

89
Q

Write the displacement reaction of the copper - H2O complex with ox (2-)

A

Cu(H2O)6 + 2ox(2-) <=> Cu(ox)2 + 6H2O

90
Q

Write the displacement reaction of the copper - Cl- complex with en

A

Cu(Cl)4 + 2(en) <=> Cu(en)2 + 4Cl-

Chemistry A - Level (26 decks)

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