23.1 - 23.5 + 24.1 - 24.3 Transition metals Flashcards
1
Q
Define transition metal
A
A metal that forms at least one stable ion with a partially filled d-shell of electrons
2
Q
List the general properties of transition metals
A
- Variable oxidation state
- Catalysis
- Complex formation
- Colour
3
Q
Define ligand
A
A molecule or ion that has a lone pair of electrons that can be donated to the transition metal
4
Q
Describe the bonds in transition metal complex ions
A
- Coordinate bonds
- Ligands donate e- pairs to the vacant d-orbitals of the transition metal
5
Q
Define coordination number
A
Number or bonds around the central metal atom or ion
6
Q
Give the prefixes that denote different numbers of ligands
A
- 6 ligands = hexa
- 4 ligands = tetra
- 2 ligands = di
7
Q
Define Lewis base
A
- e- pair donors
- In complex formations, these are ligands
8
Q
Define Lewis acid
A
- e- pair acceptor
- In complex formations, these are the transition metal ions
9
Q
Give the parts of naming transition metal complex ions
A
- No. of ligands
- Type of ligand
- Name of the metal
- Oxidation number of the metal
10
Q
Give the naming for different types of ligands
A
- H20 = aqua
- Cl- = chloro
- NH3 = ammine
- OH- = hydroxo
- CN- = cyano
11
Q
Give the naming for negatively charged metal ions
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Silver
A
Vanadium = Vanadate
Chromium = Chromate
Manganese = Manganate
Iron = Ferrate
Cobalt = Cobaltate
Nickel = Nickelate
Copper = Cuprate
Zinc = Zincate
Silver = Argentate
12
Q
Which ligands form complex ions with a tetrahedral shape?
A
- Copper
- Cobalt
- Most others
13
Q
Which ligands form complex ions with a square planar shape?
A
- Platinum
- Nickel
14
Q
Define unidente ligands
A
- Bond through only one donor atom
- e.g water, ammonia, Cl-
15
Q
Define bidente ligand
A
- Bonds through two donor atoms
- e.g 1,2-diaminoethane, ethandioate ion
16
Q
Define multidentate ligand
A
- Bonds through many donor atoms
- e.g EDTA4-
17
Q
Describe how complex ions exhibit geometric isomerism
A
Can occur in square planar and octohedral complexes
18
Q
Describe how complex ions exhibit optical isomerism
A
Can only be exhibited in complexes with bidente or multidente ligands
19
Q
Describe how transition metal complexes absorb light
A
- d-orbitals of the transition metal ions split into 2 different energy levels
- e- absorb energy from visible light
- Allows e- to move from one d-orbital to another of a higher energy
20
Q
Explain why transition metal complexes are coloured
A
- Absorbs certain visble light
- Complementary colour is reflected
21
Q
Give the equation to calculate the energy absorbed
A
change in E = hv
E = energy (J)
h = Planck’s constant (J s)
v = frequency of light absorbed (s-1)
22
Q
Give the factors that effect the amount of energy a transition metal complex absorbs
A
- The transition metal
- Type of ligand
- The co-ordination number
- Oxidation state of the transition metal
23
Q
Describe how colorimetry works
A
- Light source
- Filter to absorb all irrelevent wave lengths of light
- Tube with sample
- Light sensitve cell and meter
24
Q
What should you do if attempting colourimetry on a sample that is a very pale colour?
A
- Often hexaaqua ions are very pale
- Add a different ligand to intensify the colour
25
When do transition metals exhibit different oxidation states?
* Lower oxidation states exist as simple ions
* Higher oxidation states exist only when metals are bonded to very electronegative elecments in compound ions
26
In what conditions is it easier to oxidise a transition metal?
Alkaline
27
In what conditions is it easier to reduce a transition metal?
Acidic
28
Describe why transition metals make good catalysts
* Partially filled d-orbitals
* Allows them to alternatively accept and reject electrons, cycling between a lower and a higher oxidation state
* Allows them to help transfer electrons within reactions
29
Define homogeneous catalyst
A catalyst that is in the same phase as the reactants
| e.g Breakdown of the ozone by chlorine radicals
30
Define heterogenous catalyst
A catalyst which is in a different phase to the reactants
| e.g platinum and rhodium in catalytic converters
31
Give the equation for the Haber process and its catalyst
3H₂ + N₂ ⇌ 2NH₃
* Fe catalyst
* Catalyst lasts about 5 years before it becomes poisoned by sulphur and needs replacing
32
Give the equation for the Contact Process and its catalyst
Overall:
2SO₂ + O₂ ⇌ 2SO₃
Steps:
SO₂ + V₂O₅ → SO₃ + V₂O₄
2V₂O₄ + O₂ → 2V₂O₅
* V₂O₅ catalyst
* Needed to produce sulphuric acid
33
Give the equation for making methanol and its catalyst
CH₄ + H₂O (steam) → CO + 3H₂
CO + 2H₂ ⇌ CH₃OH
* Cr₂O₃ catalyst
* Needed for plastics such as perspex
34
Describe how adsorption of reactants onto the surface of a heterogenous catalyst increases the rate of reaction
* Brings reactants closer together and increases likelihood of collision
* May weaken bonds withing the reactant molecules
* May position the molecule in a favourable orientation for the reaction
35
Describe how catalytic efficiency is increased
* Increase surface area
* Spread or impregnate the catalyst onto an inert support medium
36
Give 2 equations to show how catalytic converters remove NO, CO and unburnt hydrocarbons
2CO + 2NO → N₂ + 2CO₂
Hydrocarbon + NO → N₂ + CO₂ + H₂O
37
Why do heterogenous catalysts need replacing?
* Finely divided catalysts can simply come off the support medium
* Poisoning - unwanted impurities block the active sites
38
Describe how homogeneous catalysts work
* Can change oxidation state
* This allows them to form an intermediate species
* Two reactions with a lower activation energy than the original single reaction
* Often used for slow reactions which require the collision of two negative ions
39
Describe the oxidation of iodide ions by peroxodisulphate
Overall:
2I⁻ + S₂O₈²⁻ → I₂ + 2SO₄²⁻
Step by step:
S₂O₈²⁻ + 2Fe²⁺ → 2SO₄²⁻ + 2Fe³⁺
2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂
* Catalysed by Fe
40
Define autocatalysis
* Where one of the products of a reaction is a catalyst for the reaction
* Catalyst does appear in overall equation
41
Describe the oxidation of ethanedioate ion by manganate (VII) ions
2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 10CO₂ + 8H₂O
* Mn²⁺ is catalyst
* MnO₄⁻ = Purple
* Mn²⁺ = Pale pink
Step by step:
* 4Mn²⁺ + MnO₄⁻ + 8H⁺ → 5Mn³⁺ + 4H₂O
* 2Mn³⁺ + C₂O₄²⁻ → 2Mn²⁺ + 2CO₂
42
What colour are copper aqua ions?
Blue
43
What colour are iron (II) aqua ions?
Green
44
What colour are iron (III) aqua ions?
Violet
45
What colour are aluminium aqua ions?
| (Not a transition metal but has similar reactions)
Colourless
46
What bonds are present in aqueous metal ions?
* Covalent bond in ligand O-H
* Coordinate bond between water and metal ion (electron pair donated by O)
47
Describe why metal aqua ions are acidic
* Metal ion pulls electron density away from the H2O ligands
* Makes them more susceptible to loss of H+
* Known as hydrolysis
48
Give the equation that explains why metal aqua ions are acidic
[M(H₂O)₆]ⁿ⁺ + H₂O ⇌ [M(H₂O)₅OH]ⁿ⁻¹⁺ + H₃O⁺
It is the H₃O⁺ that causes acidity
49
What effects the acidity of metal aqua ions?
* Small, highly charged metal ions are the most acidic
50
Name the 3 main types of reaction that metal-aqua ions undergo
* Hydrolysis (break O-H bond)
* Ligand substitution (break M-O bond)
* Redox (Add or remove electrons)
51
Describe hydrolysis reactions
Form metal hydroxides
Three possible reagents:
* OH⁻
* dilute NH₃
* CO₃²⁻
52
Describe the products of a hydrolysis reaction with OH⁻
M²⁺ = [M(H₂O)₄(OH)₂] + H₂O
M³⁺ = [M(H₂O)₃(OH)₃] + H₂O
Some M³⁺ may react further to give amphoteric hydroxides
53
Describe the products of a hydrolysis reaction with dilute NH₃
M²⁺ = [M(H₂O)₄(OH)₂] + NH₄⁺
M³⁺ = [M(H₂O)₃(OH)₃] + NH₄⁺
May get a further reaction if excess NH₃ is used, forming ammine complexes
54
Describe the products of a hydrolysis reaction with CO₃²⁻
M²⁺ = MCO₃ (ppt) + H₂O
M³⁺ = [M(H₂O)₃(OH)₃] + CO₂ + H₂O
55
Give the possible reagents for substitution reactions and their products
NH₃ (XS or conc) = Ammine complexes
Cl⁻ (conc HCl) = Chloro complexes
56
Give the equation to calculate frequency of light
Frequency (Hz) = Speed (m s-1) / Wavelength (nm)
57
Cu²⁺ as aqueous ion
[Cu(H₂O)₆]²⁺(aq) + H₂O(l) ⇌ [Cu(H₂O)₅(OH)]⁺(aq) + H₃O⁺(aq)
[Cu(H₂O)₅(OH)]⁺ = Blue solution
58
Cu²⁺, add NaOH(aq) dropwise
[Cu(H₂O)₆]²⁺(aq) + 2OH-(aq) ⇌ [Cu(H₂O)₄(OH)₂] (s) + 2H₂O(l)
[Cu(H₂O)₄(OH)₂] = Blue ppt
59
Cu²⁺, add excess NaOH(aq)
No reaction
60
Cu²⁺, add NH₃(aq) dropwise
[Cu(H₂O)₆]²⁺(aq) + 2NH₃(aq) ⇌ [Cu(H₂O)₄(OH)₂] (s) + 2NH₄⁺(aq)
[Cu(H₂O)₄(OH)₂] = Blue ppt.
61
Cu²⁺, add excess NH₃(aq)
[Cu(H₂O)₆]²⁺(aq) + 2NH₃(aq) ⇌ [Cu(NH₃)₄(H₂O)₂] (aq) + 4H₂O(l)
[Cu(NH₃)₄(H₂O)₂] = Very deep blue solution
62
Cu²⁺, add Na₂CO₃ (aq)
[Cu(H₂O)₆]²⁺(aq) + CO₃²⁻(aq) → CuCO₃(s) + 6H₂O(l)
CuCO₃ = Green ppt.
63
Cu²⁺, add conc. HCl (aq)
[Cu(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CuCl₄]²⁻(aq) + H₂O(l)
[CuCl₄]²⁻ = Yellow/green solution
64
Fe²⁺ as aqueous ion
[Fe(H₂O)₆]²⁺(aq) + H₂O(l) ⇌ [Fe(H₂O)₅(OH)]⁺(aq) + H₃O⁺(aq)
[Fe(H₂O)₅(OH)]⁺ = Pale green solution
65
Fe²⁺, add NaOH(aq) dropwise
[Fe(H₂O)₆]²⁺(aq) + 2OH⁻(aq) ⇌ [Fe(H₂O)₄(OH)₂] (s) + 2H₂O(l)
[Fe(H₂O)₄(OH)₂] = Green/grey ppt.
66
Fe²⁺, add excess NaOH
No reaction
67
Fe²⁺, add NH₃ dropwise
[Fe(H₂O)₆]²⁺(aq) + 2NH₃(aq) ⇌ [Fe(H₂O)₄(OH)₂] (s) + 2NH₄⁺(aq)
[Fe(H₂O)₄(OH)₂] = Grey/green ppt.
68
Fe²⁺, add excess NH₃
No reaction
69
Fe²⁺, add Na₂CO₃
[Fe(H₂O)₆]²⁺(aq) + CO₃²⁻(aq) → FeCO₃(s) + 6H₂O(l)
FeCO₃ = Green/grey ppt.
70
Fe²⁺, add conc. HCl
No reaction
71
Fe³⁺ as aqueous ion
[Fe(H₂O)₆]³⁺(aq) + H₂O(l) ⇌ [Fe(H₂O)₅(OH)]⁺(aq) + H₃O⁺(aq)
[Fe(H₂O)₅(OH)]⁺ = Violet solution
(Can appear somewhat orange due to unreacted [Fe(H₂O)₆]³⁺)
72
Fe³⁺, add NaOH dropwise
[Fe(H₂O)₆]³⁺(aq) + 3OH⁻(aq) ⇌ [Fe(H₂O)₃(OH)₃] (s) + 3H₂O(l)
[Fe(H₂O)₃(OH)₃] = Red/brown ppt.
73
Fe³⁺, add excess NaOH
No reaction
74
Fe³⁺, add NH₃ dropwise
[Fe(H₂O)₆]³⁺(aq) + 3NH₃(aq) ⇌ [Fe(H₂O)₃(OH)₃] (s) + 3NH₄⁺(l)
[Fe(H₂O)₃(OH)₃] = Red/brown ppt.
75
Fe³⁺, add excess NH₃
No reaction
76
Fe³⁺, add Na₂CO₃
[Fe(H₂O)₆]³⁺(aq) + CO₃²⁻(aq) ⇌ [Fe(H₂O)₃(OH)₃] (s) + 3CO₂(g) + 2H₂O(l)
[Fe(H₂O)₃(OH)₃] = Red/brown ppt.
77
Fe³⁺, add conc. HCl
No reaction
78
Al³⁺ as an aqueous ion
[Al(H₂O)₆]³⁺(aq) + H₂O(l) ⇌ [Al(H₂O)₅OH]²⁺(aq) + H₃O⁺(l)
[Al(H₂O)₅OH]²⁺ = Colourless solution
79
Al³⁺, add NaOH dropwise
[Al(H₂O)₆]³⁺(aq) + 3OH⁻(l) ⇌ [Al(H₂O)₃(OH)₃] (s) + 3H₂O(l)
[Al(H₂O)₃(OH)₃] = White ppt.
80
Al³⁺, add excess NaOH
[Al(H₂O)₆]³⁺(aq) + 4OH⁻(l) ⇌ [Al(H₂O)₂(OH)₄]⁻(aq) + 4H₂O(l)
[Al(H₂O)₂(OH)₄]⁻ = Colourless solution
81
Al³⁺, add NH₃ dropwise
[Al(H₂O)₆]³⁺(aq) + 3NH₃(aq) ⇌ [Al(H₂O)₃(OH)₃] (s) + 3NH₄⁺(aq)
[Al(H₂O)₃(OH)₃] = White ppt.
82
Al³⁺, add excess NH₃
No reaction
83
Al³⁺, add Na₂CO₃
[Al(H₂O)₆]³⁺(aq) + CO₃²⁻(aq) ⇌ [Al(H₂O)₃(OH)₃] (s) + 3CO₂(g) + 2H₂O(l)
[Al(H₂O)₃(OH)₃] = White ppt.
84
Al³⁺, add conc. HCl
No reaction
85
Explain why an aqueous solution containing [Fe(H2O)6] 3+ ions has a lower pH than an aqueous solution containing [Fe(H2O)6]
2+ ions
* Fe3+ is smaller and has a greater charge
* Fe3+ ions polarise water molecules more
* Weakens O-H bond in H2O ligand
* So more water ligand O-H bonds break, releasing more H+
86
Describe EDTA
* -4 charge
* Hexadentate
87
What should be given when excess of water is added to ion?
* Hexaaqua ion
* There is much more of this than of the other ion
88
Give the titration equations that must be memorised
MnO₄⁻ + 5e⁻ → Mn²⁺
Cr₂O₇²⁻ + 6e⁻ → Cr³⁺
89
Also learn
* Bidente ligand
* Cisplatin
90
[Fe(H₂O)₆]³⁺ → [Fe(H₂O)₆]²⁺
What reagent is needed for this reaction?
Zn in acid
91
Copper (I) iodide is a white solid. Why?
* Full d-orbital
* So no d-d transitions
* Cannot absorb any visible light so appears white
