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TRANSITION METALS Flashcards

1
Q

What is a ligand substitution reaction?

A

Where one ligand can be swapped for another ligand

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2
Q

During a ligand sibstitution reaction, what must happen to ensure that both the coordination number and shape stay the same?

A

The ligands must be of similar size, e.g water and ammonia

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3
Q

Give the similarities between ammonia and water ligands:

A

similar size and uncharged so they can be exchanged with each other without any change in co-ordination number or shape

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4
Q

What does a ligand substitution reaction always result in, no matter the size of the ligand?

A

A colour change

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5
Q

Give an equation representing a ligand substitution reaction where [Co(H20)6] 2+ reacts with an excess of ammonia:

A

[Co(H20)6] 2+ + 6NH3 –> [Co(NH3)6] 2+ + 6H20

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6
Q

Give the coordination number change, the shape and the colour change of the conversion of [Co(H20)6] 2+ INTO [Co(NH3)6] 2+

A

Goes from pink to straw coloured
Shape remains octahedral
Coordination number remains as 6.
THERE IS ALWAYS A COLOUR CHANGE WHEN THERE IS A CHANGE IN LIGAND

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7
Q

If the ligands are different sizes to each other e.g. Cl- is bigger than NH3/H20, then what changes?

A

There is a change in coordination number and shape

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8
Q

Give the colour change, the shape and the coordination numbers for the conversion of [Cu(H20)6]2+ INTO [CuCl4]2- :

A

Goes from octahedral to tetrahedral
Coordination number goes from 6 to 4
Colour change from pale blue to yellow-green

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9
Q

What is the equation for the reaction between a copper-aqua ion and 4Cl- ligands?

A

[Cu(H20)6]2+ + 4Cl- –> 6H20 + [CuCl4]2-

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10
Q

Give an example of a partial substitution reaction:

A

[Cu(H20)6]2+ + 4NH3 –> [Cu(NH3)4(H20)2] 2+ + 4H20

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11
Q

What is the shape change, the coordination number and colour change for the partial substitution reaction: [Cu(H20)6]2+ + 4NH3 –> [Cu(NH3)4(H20)2] 2+ + 4H20

A

Octahedral to elongated octahedral
Pale blue to deep blue
Coordination number remains 6

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12
Q

What is haemoglobin and what does it do?

A

A proteins found in the blood which helps to transport oxygen around the body

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13
Q

What transition metal ion does haemoglobin contain?

A

Fe2+

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14
Q

Fe2+ ions are hexa-co-ordinated. What does that mean?

A

Six lone pairs are donated to them to form 6 co-ordinate bonds

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15
Q

Haem is part of the haemoglobin molecule, what is the haem group made up of?

A

Four of the lone pairs which are donated to the Fe2+ come from the nitrogen atoms which forms a circle around the Fe2+ - THIS IS CALLED HAEM

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16
Q

In haemoglobin, what molecule is the nitrogen atom a part of?

A

They are part of a multidentate ligand called porphyrin

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17
Q

Apart from haem, what are the other parts that make up haemoglobin?

A

Either an oxygen or water molecule also bind to the Fe2+ ion - to form an octahedral structure
AND a protein called globin also makes up the structre of haemoglobin

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18
Q

How does oxygen get transported around the body with the use of haemoglobin? Describe the role of water in this as well:

A

Both oxygen and water will bind to Fe2+ as ligands so the complex can transport oxygen to where it is needed and then swap for H20

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19
Q

Describe the what happens IN THE LUNGS concerning haemoglobin:

A

O2 conc is high in lungs so water ligands are substituted for O2 to form oxyhaemoglobin which is carried around the body in blood.
When oxyhaemoglobin gets to a place where oxygen is needed - oxygen molecules are exchanged for water molecules
The haemoglobin returns to the lungs and the process starts again.

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20
Q

Describe what happens during carbon monoxide poisoning:

A

When CO is inhaled, haemoglobin can substitute its water ligands for CO ligands instead of O2 ligands and it forms carboxyhaemoglobin

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21
Q

Why does carbon monoxide poisoning occur?

A

CO forms a very strong bond with Fe2+ ions and doesn’t readily exchange with oxygen or water ligands. The haemoglobin can’t transport oxygen anymore.

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22
Q

What does CO poisoning do and what are the symptoms?

A

It starves the organs of oxygen - causes headaches, dizziness, unconsciousness and death

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23
Q

What is the haemoglobin molecule called when oxygen is bonded to it?

A

Oxyhaemoglobin

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24
Q

What is the haemoglobin molecule called when water has displaced the oxygen ligand?

A

Deoxyhaemoglobin

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25
What makes a complex ion more stable than another?
If the new ligands form stronger bonds with the central metal ion - the change is less easy to reverse
26
Normally, ligand substitution reactions can be easily reversed, give one reason why this might not be possible?
UNLESS the new complex ion is much more stable than the previous one
27
Give an example showing different complex ion stabilities:
CN- ions form stronger coordinate bonds than water molecules do with Fe3+ So the complex formed with CN- ions will be more stable than the one formed with H20 ligands So the substitution of water molecules with CN- ions in an iron(III) complex IS HARD TO REVERSE
28
Give the equation for the substitution of water molecules for CN- ions in an Fe3+ complex:
[Fe(H20)6]3+ + 6CN- --> [Fe(CN)6]3+ + 6H20
29
What type of ligand forms a more stable complex ion?
Multidentate form more stable complexes than monodentate ligands
30
Reactions involving what two types of ligands, are hard to reverse?
Reactions involving multidentate and bidentate ligands are hard to reverse
31
Give an example that shows how type of ligands affects the stability of the complex ion formed:
Complexes that contain the bidentate ligand 'ethane-1,2-diamine' are more stable than those that contain water molecule ligands So, reactions where water molecules are substituted by ethane-1,2-diamine, are HARD TO REVERSE
32
In terms of bonds, what does a ligand exchange/substitution reaction contain?
Bonds being broken and formed
33
Why is the enthalpy change for a ligand substitution reaction usually very small?
Because the strength of the bonds being broken is often very similar to the bonds being made
34
Give an example of a ligand sub reaction that has a small enthalpy change:
Substituting ammonia with ethane-1,2-diamine in a nickel complex
35
Is the substitution of ammonia with ethane-1,2-diamine in a nickel complex reversible or irreversible?
It is actually REVERSIBLE but because the equilibrium lies so far to the right, it is thought of as being IRREVERSIBLE
36
Describe the entropy change for when a monodentate ligand is substituted by a bi/multidentate ligand? And why this happens?
The number of particles increases so there is an increase in entropy MORE PARTICLES = GREATER ENTROPY
37
What reactions are MORE LIKELY to occur in terms of entropy? What does this mean in terms of complex ion stability?
Reactions that result in an increase in entropy are more likely to occur. This is why multidentate ligands always form much more stable complex ions than monodentate ligands.
38
What is the chelate effect?
When a multidentate forms one coordinate bond with the central ion compared to two monodentate molecules forming two coordinate bonds with the central metal ion. The complex containing the multidentate always form much more stable complex ions
39
State whether there was an increase/decrease/no change in entropy here: [Ni(NH3)6]2+ + 3NH2CH2CH2NH2 --> [Ni(NH2CH2CH2NH2)3]2+ + 6H3
There is an increase in entropy as there was 4 molecules and an increase to 7 molecules So the more stable molecule is the one that has been formed [Ni(CH2NH2NH2CH2)3]2+
40
What else can replace mono/bidentate ligands to make the complex more stable?
When the hexadentate ligand EDTA4- replaces the mono/bidentate ligands, the complex formed is much more stable so the reaction is DIFFICULT TO REVERSE
41
Why is the reaction difficult to reverse when you are replacing mono/bidentate ligands with EDTA4-?
Because reversing them would cause a decrease in the system's entropy
42
Give an equation showing the substitution of mono/bidentate ligands for hexadentate ligands such as EDTA4-:
[Cr(NH3)6]3+ + EDTA4- --> [Cr(EDTA)]- + 6NH3
43
Describe the change in entropy for this reaction: [Cr(NH3)6]3+ + EDTA4- --> [Cr(EDTA)]- + 6NH3
From 2 molecules to 7 molecules so entropy increases and therefore the [Cr(EDTA)]- molecule is much more stable
44
What is the chelate effect due to?
Both enthalpy and entropy
45
What can transition metals form more than one type of? What is different in each of these?
More than one type of ions and in different ions they have different oxidation states
46
What is a redox reaction?
When you switch between oxidation states
47
How many oxidation states can vanadium exist in?
4
48
What are vanadiums different oxidation states?
+2 , +3 , +4 , +5
49
When vanadium has the oxidation state, +5, what is the formula of the ion and the colour of the ion?
VO2 (+) YELLOW
50
When vanadium has the oxidation state, +4, what is the formula of the ion and the colour of the ion?
VO (2+) BLUE
51
When vanadium has the oxidation state, +3, what is the formula of the ion and the colour of the ion?
V(3+) GREEN
52
When vanadium has the oxidation state, +5, what is the formula of the ion and the colour of the ion?
V(2+) VIOLET
53
How can the vanadium in ammonium vanadate(V) be reduced?
By adding it to (XS) zinc metal in an acidic solution e.g.H2SO4/HCl
54
Give the equation when vanadium(V) is reduced to vanadium(IV)?
2VO2(+) + Zn + 4H+ --> 2VO(2+) + Zn2+ + 2H2O
55
What is the colour change when vanadium(V) is reduced to vanadium(IV)?
YELLOW --> BLUE
56
What is the equation when vanadium (IV) is reduced to vanadium (III)?
2VO(2+) + Zn + 4H+ --> 2V(3+) + Zn(2+) + 2H2O
57
What is the colour change when vanadium (IV) is reduced to vanadium (III)?
BLUE --> GREEN
58
What is the equation when vanadium(III) is reduced to vanadium(II)?
2V(3+) + Zn --> 2V(2+) + Zn(2+)
59
What is the colour change when vanadium(III) is reduced to vanadium(II)?
GREEN --> VIOLET
60
What does the redox potential of an ion/atom tell you?
It tells you how easily it is reduced to a LOWER oxidation state
61
What are redox potentials the same as?
Electrode potentials
62
What is the relationship between redox potentials and the stability of an ion?
The MORE POSITIVE the redox potential = LESS STABLE ION which means the ion is more likely to be reduced
63
Redox potential of copper(II) is +0.15V and chromium(II) is -0.74V. Which ion is the most stable and why?
The chromium(II) because it has the more negative redox potential which means it has the most stable ion as it is less likely to be reduced.
64
What is the formula of the vanadate(V) ion?
VO2(+)
65
What causes the redox potential to vary from the electrode potential?
It depends on the environment that the ion is in?
66
What two factors affect redox potential?
pH and ligands
67
Describe how ligands can cause the redox potential to vary from standard electrode potentials?
Standard electrode potentials are measured in aq solution, so any ions will be surrounded by water ligands Different ligands may make the redox potential larger/smaller dpeending on how well they bind to the metal ion in a particular oxidation state
68
What is the GENERAL relationship between pH and redox potentials?
Generally, more acidic solutions give MORE POSITIVE redox potentials therefore the ion is more easily reduced
69
What are the two ways in which ions can be reduced? And for reactions such as these, what affects the size of the redox potential?
They either gain H+ ions or release OH- ions in order to be reduced. pH affects the size of the redox potential.
70
Describe silver inclu. common oxidation state and what type of element. What is it reduced to?
Silver is a transition metal commonly found in the +1 oxidation state. And it is easily reduced to silver metal
71
Give the equation for the reduction of silver to silver metal:
Ag+ (aq) + e- --> Ag(s)
72
Why is the reduction of silver to silver metal important? What is it used in?
Tollen's reagent uses this reduction reaction to distinguish between aldehydes and ketones
73
How is Tollen's reagent prepared?
By adding just enough ammonia solution to silver nitrate solution = this forms a colourless solution containing the complex: [Ag(NH3)2]+
74
What complex ion does Tollen's reagent contain?
[Ag(NH3)2]+
75
When Tollen's reagent reacts with aldehydes, what happens?
A silver mirror is formed, the aldehyde is oxidised to a carboxylate anion and the Ag+ ions are reduced to silver metal.
76
Give the equation of an aldehyde reacting with Tollen's reagent:
RCHO(aq) + 2[Ag(NH3)2]+ (aq) + 3OH- --> RCOO- (aq) + 2Ag(s) + 4NH3(aq) + 2H2O(l)
77
What reaction happens when Fehling's solution reacts with an aldehyde?
It gives a brick red precipitate of Cu2O
78
In what conditions is it easier to oxidise a transition metal?
ALKALINE CONDITIONS
79
In what conditions is it easier to reduce a transition metal?
ACIDIC CONDITIONS
80
What type of solution do metal-aqua 2+ ions form? So what ion does this mean they release?
They form weakly acidic solutions because they only slightly dissociate and they release H+ ions.
81
Show the dissociation of a metal-aqua 2+ ion in water using an equation? Use iron as an example:
[Fe(H2O)6]2+ (aq) + H2O(l) <--> [Fe(OH)(H2O)5] + (aq) + H3O+ (aq)
82
What is the formula of a hydroxonium ion?
H3O+
83
Show the dissociation of a metal-aqua 3+ ion in water using an equation? Use aluminium as an example:
[Al(H2O)6]3+ (aq) + H2O(l) <--> [Al(OH)(H2O)5]2+ (aq) + H3O+(aq)
84
Describe why metal-aqua 3+ ions form more acidic solutions than metal-aqua 2+ ions?
Metal-aqua 3+ ions are pretty small but they have a high charge density whereas metal-aqua 2+ ions have a much lower charge density. This makes the 3+ ions much more polarising than the 2+ ions. --> more polarising power means that theu can attract electrons from the oxygen atoms
85
Give the overall equation for the full hydrolysis of metal-aqua 3+ ions using iron as an example:
[Fe(H2O)6]3+ (aq) + 3H2O <--> Fe(OH)3(H2O)3 (s) + 3H3O+
86
Give the three separate equations for the full hydrolysis of a metal-aqua 3+ ion using iron as an example:
[Fe(H2O)6]3+ (aq) + H2O(l) <--> [Fe(OH)(H2O)5]2+(aq) + H3O+(aq) [Fe(OH)(H2O)5]2+ (aq) + H2O(l) <--> [Fe(OH)2(H2O)4]+(aq) + H3O+(aq) [Fe(OH)2(H2O)4]+ (aq) + H2O(l) <--> [Fe(OH)3(H2O)3](s!!) + H3O+(aq)
87
All metal hydroxide precipitates will dissolve in what? And what do they act as?
They will all dissolve in acid and they act as Bronsted-Lowry bases as they accept H+ ions.
88
What reverses the hydrolysis reactions of the metal-aqua ions?
The dissolving of the metal hydroxide ppts in acid
89
Show the 3 separate equations which represent 'Adding an acid to iron(III) hydroxide which results in the reforming of the soluble metal-aqua ion'
Fe(OH03(H2O)3 (s) + H+ <--> [Fe(OH)2(H2O)4]+(aq) [Fe(OH)2(H2O)4]+(aq) + H+ <--> [Fe(OH)(H2O)5]2+ (aq) [Fe(OH)(H2O)5]2+ (aq) + H+ <--> [Fe(H2O)6] 3+ (aq)
90
Give the overall equation for 'Adding an acid to iron(III) hydroxide which results in the reforming of the soluble metal-aqua ion'
91
Give an example of a metal hydroxide that can act ampohteric:
Al(OH)3(H2O)3 Aluminium hydroxide is amphoteric
92
Give an equation showing aluminium hydroxide acting as an acid:
Al(OH)3(H2O)3 (s) +OH- (aq) <--> [Al(OH)4(H2O)2]- (aq) + H2O(l)
93
How does aluminium hydroxide act as a Bronsted Lowry acid? in words:
It donates H+ ions to the OH- ions
94
Give an equation showing aluminium hydroxide acting as a base:
Al(OH)3(H2O)3 (s) + 3H+ <--> [Al(H2O)6]3+ (aq)
95
During the hydrolysis of metal-aqua ions, what can you use to add hydroxide ions?
Ammonia solution or the obvious way is to use a strong alkali e.g. NaOH
96
How can ammonia solution be used to add OH- ions to metal-aqua ions?
When NH3 dissolves in water - it can accept protons from the water molecules to form NH4+ ions and OH- ligands
97
What solution gives the same result as NaOH in regards the hydrolysis of metal-aqua ions?
Ammonia solution gives the same result as adding NaOH
98
Give the equation for the reaction between [Fe(H2O)6]3+ (aq) and ammonia:
[Fe(H2O)6]3+ (aq) + 3NH3(aq) <--> [Fe(OH)3(H2O)3] (s) + 3NH4+ (aq)
99
Describe the appearance of [Fe(H2O)6]3+ (aq)
YELLOW SOLUTION
100
Describe the appearance of [Fe(OH)3(H2O)3] (s)
BROWN PRECIPITATE
101
Sometimes a further reaction can happen once ammonia has reacted with metal-aqua ions, what must the conditions be in order for this to happen?
If you add an excess of ammonia
102
Give an equation representing the further reaction of NH3 with [Cu(OH)6]4- (aq) and describe what happens?
OH- and H2O ligands are displaced by NH3 ligands EQUATION: [Cu(OH)6]4- (aq) + 4NH3 (aq) <--> [Cu(NH3)4(H2O)2]2+ (aq) + 6OH- (aq)
103
Further reactions for the reaction between ammonia and metal-aqua ions happens with which complexes?
Cu2+ complexes
104
Describe the appearance of [Cu(OH)6]4- (aq)
PALE BLUE SOLUTION
105
Describe the appearance of [Cu(NH3)4(H2O)2]2+ (aq)
DARK BLUE SOLUTION
106
What is formed when metal 2+ ions react with sodium carbonate?
INSOLUBLE metal carbonates
107
What are the four characteristic properties of transition metals?
Complex formation Variable oxidation states Formation of coloured ions Catalytic activity
108
What is a ligand?
A molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons
109
What is a complex?
Where a central metal ion is surrounded by ligands which are coordinately bonded to it
110
What is the coordination number?
The number of co-ordinate bonds to the central metal atom/ion
111
Give three examples of monodentate ligands:
NH3, Cl-, H2O
112
Give two examples of bidentate ligands:
H2N-CH2CH2-NH2 and C2O4-
113
Give one example of a monodentate ligand:
EDTA4-
114
Haem is an ...... complex with a ......... ligand?
iron (II) multidentate
115
What is the chelate effect? (AQA definition)
Where bidentate and multidentate ligands replace monodentate ligands from complexes
116
What type of isomerism canoctahedral complexes form and with which ligands?
Octahedral complexes can form E/Z isomerism with monodentate ligands and they can form optical isomerism with bidentate ligands
117
How does colour arise in a transition metal ion?
When some of the wavelengths of visible light are absorbed so d-electrons move from the ground state to their excited state and the remaining wavelengths of light are transmitted or reflected
118
What equation gives the energy difference between the ground state and the excited state of the d-electrons
∆E = hν = hc/λ
119
What 3 factors alter ∆E?
Change in ligand Change in oxidation state Change in co-ordination number
120
What does a change in ∆E lead to?
A change in colour
121
What can be used to determine the concentration of coloured ions in solution?
A simple colorimeter
122
Give the equation for the formation of metal carbonates from metal 2+ ions: use 'M' to represent the metal
[M(H2O)6]2+ (aq) + CO3(2-) (aq) <--> MCO3 (s) + 6H2O (l)
123
Describe the reaction of metal 3+ ions with sodium carbonate and describe why M2(CO3)3 doesn't form?
M2(CO3)3 doesn't form because M3+ ions are stronger acids so they always form hydroxide precipitates instead. The carbonate ions react with the the H3O+ ions, which removes them from the solution and forms bubbles of CO2 gas.
124
Give the equation of M3+ ions reacting with sodium carbonate using 'M' as the metal:
2[M(H20]6]3+ (aq) + 3CO3 (2-) (aq) <--> 2M(OH)3(H2O)3 (s) + 3CO2(g) + 3H2O (l)
125

A Level Chemistry (17 decks)

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