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Chemistry A Level > 2.5 Transition Metals > Flashcards

2.5 Transition Metals Flashcards

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1
Q

What is a transition metal?

A

An element whose atom has an incomplete d sub-shell or which can give rise to cations with an incomplete d sub shell

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2
Q

What are some key properties of transition metals?

A
  • Transition metals are often coloured
  • Most are catalytically active
  • Variable oxidation state
  • Form complex ions where the transition metal ion is bonded to other ions or molecules via coordinate bonds.
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3
Q

What is a ligand?

A

A ligand is an ion or molecule with a lone pair of electrons that is available to form a coordinate bond with a transition metal.

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4
Q

What is the coordination number?

A

Coordination number of a transition metal complex is the number of coordinate bonds to ligand surrounding a transition metal ion

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5
Q

What is an unidentate ligand?

A

A molecule or ion that can donate one pair of electrons

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6
Q

What is a bidentate ligand?

A

A molecule or ion that can donate two pairs of electrons

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7
Q

What is a multidentate ligand?

A

A molecule or ion that can donate more than two pairs of electrons

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8
Q

Give examples of unidentate ligands

A

Water, ammonia

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9
Q

Give examples of bidentate ligands

A

Ethanedioate ions, 1,2-diaminoethane

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10
Q

Give examples of multidentate ligand

A

EDTA 4-

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11
Q

What does the overall complex charge depend upon?

A

The charge of the central metal ion and the charge on its ligands

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12
Q

What is the anionic complex name for cobalt?

A

Cobaltate

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13
Q

What is the anionic complex name for copper?

A

Cuprate

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14
Q

What is the anionic complex name for iron?

A

Ferrate

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15
Q

What is the anionic complex name for nickel?

A

Nickelate

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16
Q

What is the anionic complex name for silver?

A

Argentate

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17
Q

What is the anionic complex name for vanadium?

A

Vanadate

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18
Q

When are square planar complexes formed, and give an example?

A

With Pt2+ complexes, eg [PtCl4]2-

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19
Q

When are tetrahedral ligand complexes formed, and give an example?

A

With large ligands (eg Cl-), eg [CuCl4]2-

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20
Q

When are linear ligand complexes formed, and give an example?

A

With Ag+ complexes, eg [Ag(NH3)2]+

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21
Q

What is the name of the ligand water in a complex?

A

Aqua

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22
Q

What is the name of the ligand hydroxide in a complex ?

A

Hydroxo

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23
Q

How do catalysts work (in terms of forming intermediates/products/etc)

A
  • Reactants react with catalyst forming an intermediate.

- Intermediate reacts to form product faster than original product

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24
Q

Why are transition metal complexes coloured?

A

Trasition metal compounds have partly filled d orbitals, meaning that it is possible for electrons to move from one orbital to another. In a compound the presence of other atoms makes the d orbitals have slightly different energy. When electrons move from one orbital to another they absorb energy in the bisible region of the spectrum, meaning a certain colour is missing, and absorbed.

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25
Q

What happens to the d-orbitals of an atom when a transition metal complex is formed?

A

The d orbitals have slightly different energies.

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26
Q

When electrons move from one d-orbital to another one of a higher energy level, whay do they do?

A

They absorb energy in the visible region of the spectrum equal to the difference in energy between levels.

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27
Q

What is the colour of a transition metal complex dependent on?

A

The energy gap (🔺E), which in turn depends on the oxidation state of the metal and on the ligands.

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28
Q

How do you calculate the energy difference between d-orbitals?

A

🔺E = hv
🔺E - energy change
V - frequency
h- planck’s constant.

29
Q

How can we make heterogeneous catalysts more efficient?

A

Increase the surface area, eg by spreading the catalyst onto an inert support medium (eg a mesh or ceramic material)

30
Q

What is autocatalysis?

A

When one of the products of a reaction also acts as a catalyst fot the reaction.

31
Q

Give the hydrolysis reaction for Hexaaquacopper.

A

[Cu(H2O)6]2+ + H2O <=> [Cu(H2O)5(OH)]+ + H3O+

32
Q

What is formed when [Cu(H2O)5(OH)]+ is hydrolysed?

A

[Cu(H2O)4(OH)2] which has no overall charge, meaning a blue precipitate is formed.

33
Q

What can be used to shift a hydrolysis reaction involving transition metal complexes to the right?

A

use ammonia or sodium/potassium hydroxide, as this reacts with the hydroxonium ion, lowering this concentration and forcing the equilibria to the right.

34
Q

Give examples of amphoteric transition metal complexes.

A

Aluminium hydroxide/aqua and chromium hydroxide/aqua

35
Q

Give an equation for the ligand exchange of hexaaquachromium with ammonia.

A

[Cr(H2O)6]2+ + 6NH3 <=> [Cr(NH3)6]2+ + 6H2O

36
Q

What occurs when excess ammonia is added to hexaaquacopper(II)

A

Complete ligand exchange does not occur. Instead substitution is incomplete, resulting in tetraamminediaqua copper [Cu(NH3)4(H2O)2]2+

37
Q

How are the ammine ligands arranged in tetraamminediaqua copper(II)

A

In a square planar shape

38
Q

Give an equation for the ligand exchange begween a hexaaqua complex and chloride ions.

A

[M(H2O)6]3+ + 4Cl- <=> [MCl4]- + 6H2O

39
Q

Why does a ligand exchange involving chloride ions and hexa aqua complexes involve a change in coordination number?

A

Because chloride ions are larger than H2O/NH3

40
Q

What is chelation?

A

Chelation occurs when the unidentate ligands are substituted for a bidentate or multidentate ligand, resulting in a more stable complex

41
Q

What is a chelate?

A

A complex containing bidentate or multidentate ligands

42
Q

Why is the enthalpy change during a ligand exhange approximately zero.

A

Because there is very little change in coordinate bond strength/enthalpy between different ligands, meaning little energy is absorbed/released

43
Q

Describe the entropy change during chelation.

A

There is more molecules in the products following chelation, meaning that there is a greater entropy in the forward reaction.

44
Q

Describe the colour change when an aqueous Fe2+ ion has

  • NaOH added
  • NH3 added
  • Na2CO3 added
A

Turns from a green solution to

  • Dark green precipitate
  • Dark green precipitate
  • Green precipitate
45
Q

Describe the colour change when an aqueous Cu2+ ion has

  • NaOH added
  • NH3 added
  • Excess NH3 addes
  • Na2CO3 added
A

Turns from a blue solution to a

  • Light blue precipitate
  • Light blue precipitate
  • Deep blue solution
  • Blue-green precipitate
46
Q

Describe the colour change when an aqueous Fe3+ ion has

  • NaOH added
  • NH3 added
  • Na2CO3 added
A

Turns from a purple solution to

  • Brown precipitate
  • Brown precipitate
  • Brown precipitate + effervescence
47
Q

In what conditions (acidic or alkaline) does the reduction of a transition metal take place?

A

Acidic conditions

48
Q

In what conditions (acidic or alkaline) does the oxidation of an transition metal take place?

A

Alkaline conditions

49
Q

What are transition metals often reduced using?

A

Zinc and Hydrogen ions.

50
Q

Give the species of when vanadium is in the V+5 oxidation state (and its colour)

A

VO2+, yellow solution

51
Q

Give the species of when vanadium is in the V+4 oxidation state (and its colour)

A

VO^2+, blue solution

52
Q

Give the species of when vanadium is in the V+3 oxidation state (and its colour)

A

[V(H2O)6]^3+, green solution

53
Q

Give the species of when vanadium is in the V+2 oxidation state (and its colour)

A

[V(H2O)6]^2+ , purple solution

54
Q

What oxidation states do transition metals typically exhibit?

A

Both 1+ and 2+, which is formed by the loss of 4s electrons

55
Q

Do higher oxidation states of transition metals exist as ions?

A

No, only lower states (eg Mn2+ does exist as an ion but Mn7+ does not), with higher states existing in certain compounds (eg Mn7+ exists in MnO4^- through covalent bonding)

56
Q

Does Manganate ions (MnO4^-) act as a reducing or oxidising agent?

A

Oxidising agent, changing from a purple solution to a colourless solution

57
Q

When is the end point during oxidation using MnO4^-

A

When potassium manganate no longer loses its purple colour (ie first tinge of pink)

58
Q

During oxidation using MnO4^- should conditions be acidic or alkaline?

A

Conditions must be acidic using dilute sulfuric acid.

59
Q

Name some unsuitable acids for oxidation using MnO4^-

A
  • HCl as MnO4- would oxidise Cl- to Cl2 and increase titre volume
  • Concentrated Sulfuric and Nitric acid as they are oxidising agents so would lower titre volume
  • Ethanoic acid is too weak
60
Q

Give the redox equation for the analysis of Fe2+ ions in solution

A

5Fe^2+ + MnO4^- + 8H+ -> 5Fe^3+ + Mn^2+ + 4H2O

61
Q

What is the ratio of Iron(II) to Manganate ions?

A

5:1

62
Q

What issue is there with the method of analysing Fe2+ ions using MnO4^- (and how can this be solved)?

A
  • This can only measure the number of Fe2+ ions as Fe3+ wont oxidise
  • First all Fe3+ must be reduced using zinc (then filter off zinc) then retry.
63
Q

What can we use to analyse a solid sample of iron?

A

Use concentrated acid to dissolve it.

64
Q

Describe how heterogenous catalysts catalyse reactants

A

Reactants adsorbed onto surface of catalysts
This:
- Weakens bonds.
- Brings reactants close together.
- Orientates reactants in a favourable orientation.
- Once reaction is complete products are desorbed. (leaves surface)

65
Q

Why is this reaction :
S2O8^2- + 2I- -> 2SO4^2- + I2
Slow?

A

The reaction is slow as both reactants are negatively charged so repel each other.

66
Q

What can be used to catalyse this reaction:

S2O8^2- + 2I- -> 2SO4^2- + I2

A

Fe(II) ions

67
Q

Give the catalysed reaction using Fe(II) ions in this reaction

S2O82- + 2I- → 2SO42- + I2

A

Step 1 : S2O8^2- + 2Fe^2+ -> 2SO4^2- + 2Fe^3+

Step 2 : 2Fe^3+ 2I- -> 2Fe2+ + I2

68
Q

Give the reaction for the autocatalysis of the reaction between Manganate ions and ethanedioate ions

A

Step1: 2MnO4- + 16H+ + 8Mn2+ → 10Mn3+ +8H2O
Step2: 5C2O42- + 10Mn3+ → 10CO2 + 10Mn2+

69
Q

How do you calculate 🔺E from f and/or (lambda)

A

🔺E = hf = hc/(lambda)

Chemistry A Level (35 decks)

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