Transition Metals Flashcards
(123 cards)
1
Q
What is the d-block?
A
The block of elements in the middle of the periodic table.
Most of the elements in the d-block are transition elements.
2
Q
TRANSITION METAL
A
A metal that can form one or more stable ions with a partially filled d-subshell.
3
Q
How many electrons can the d-subshell fit?
A
10
4
Q
What must transition metals form?
A
At least one ion that has between 1 and 9 electrons in the d-subshell.
5
Q
What are the rules for writing the electron configurations of elements?
A
- Electrons fill up the lowest energy subshells first.
- Electrons fill orbitals singly before they start sharing.
- 4s subshell usually fills before 3d.
6
Q
Why does the 4s subshell fill first?
A
It has a lower energy level than the 3d subshell.
7
Q
What are the exceptions to the regular rules of electron configuration?
A
- Chromium prefers to have one electron in each orbital of the 3d subshell and just one in the 4s subshell- this gives more stability.
- Copper prefers to have a full 3d subshell and just one electron in the 4s subshell- more stable that way.
8
Q
Why are scandium and zinc not transition metals?
A
Their stable ions don’t have partially filled d-subshells.
Scandium only forms Sc3+, which has an empty
d-subshell.
Electron config. [Ar] 3d1 4s2
so when it loses 3 electrons, it has the electron config [Ar].
Zinc only forms one ion, Zn2+, which has a full d-subshell. Zinc has the electron config. [Ar] 3d10 4s2.
When it forms Zn2+ it loses two electrons, both from the 4s subshell. Keeps full 3d subshell.
9
Q
What kind of ions do transition metal atoms form?
A
positive ions
10
Q
Where are the electrons removed from first when a transition ion is formed?
A
s electrons are removed first.
11
Q
What are the physical properties of transition metals?
A
- All have a high density.
- They all have high melting and high boiling points.
- Their ironic radii are more or less the same.
12
Q
What are the chemical properties of transition metals?
A
- They can form complex ions.
e. g. iron forms a complex ion with water [Fe(H2O)6]2+ - They form coloured ions.
e. g. Fe2+ ions are pale green and Fe3+ ions are yellow. - They’re good catalysts.
e. g. iron is the catalyst used in the Haber process.
-They can exist in variable oxidation states.
E.g. iron can exist in the +2 oxidation state as Fe2+ ions and in the +3 oxidation state as Fe3+ ions.
13
Q
What are the common coloured ions and their oxidation states of Vanadium? (Colours refer to their aqueous ion)
A
V2^+/+2/violet
V3^+/+3/green
VO^2+/+4/blue
VO2^+/+5/yellow
14
Q
What are the common coloured ions and their oxidation states of Chromium? (Colours refer to their aqueous ion)
A
Cr^3+/+3/green/violet
Cr2O7^2-/+6/orange
15
Q
What are the common coloured ions and their oxidation states of Manganese? (Colours refer to their aqueous ion)
A
Mn2+/2+/pale pink
MnO4-/+7/purple
16
Q
What are the common coloured ions and their oxidation states of Iron? (Colours refer to their aqueous ion)
A
Fe2+/+2/pale green
Fe3+/+3/yellow
17
Q
What are the common coloured ions and their oxidation states of Cobalt? (Colours refer to their aqueous ion)
A
Co2+/+2/pink
18
Q
What are the common coloured ions and their oxidation states of Nickel? (Colours refer to their aqueous ion)
A
Ni2+/+2/green
19
Q
What are the common coloured ions and their oxidation states of Copper? (Colours refer to their aqueous ion)
A
Cu2+/+2/blue
20
Q
Why do the transition elements show variable oxidation states?
A
The energy levels of the 4s and 3d subshells are very close to one another. So different numbers of electrons can be gained or lost using fairly similar amounts of energy.
21
Q
What causes the special chemical properties of transition metals?
A
The incomplete d-subshell.
22
Q
What are complex ions?
A
A complex ion is a metal ion surrounded by co-ordinately bonded ligands.
23
Q
What is a co-ordinate bond (dative covalent)?
A
A covalent bond in which both electrons in the shared pair come from the same atom.
24
Q
Where does the electron pair come from in a complex?
A
From the ligands.
25
What is a ligand?
An atom, ion or molecule that donates a pair of electrons to a central metal ion.
26
What must a ligand have?
At least one lone pair of electrons, or it won't have anything to use to form a coordinate bond.
27
What can different ligands have?
Can have different numbers of lone pairs and can form different numbers of coordinate bonds.
28
UNIDENTATE
Ligand that can only form one coordinate bond.
29
MULTIDENTATE
Ligands that can form more than one coordinate bond.
30
Give 3 examples of unidentate ligands.
Ammonia :NH3
Chloride ions :Cl-
Water H2O:
31
Give two examples of multidentate ligands.
EDTA4-
EDTA4- has 6 lone pairs (2 on nitrogen, 4 on oxygen)
so can form 6 coordinate bonds.
32
BIDENTATE
Multidentate ligands that can form two coordinate bonds.
33
Give an example of a bidentate ligand.
Ethane-1,2-diamine (:NH2CH2CH2:NH2)
34
What is the overall charge on a complex ion?
It's total oxidation state. Put outside brackets.
35
How do you work out the oxidation state of the metal ion within a complex?
The oxidation state of metal ion= The total oxidation state of the complex - The sum of the oxidation state of the ligands.
36
What does the shape of complex ions depend on?
The coordination number.
37
COORDINATION NUMBER
The number of coordinate bonds that are formed with the central metal ion.
38
What shape do complex ions that contain six coordinate bonds make?
OCTAHEDRAL SHAPE
39
What shape do complex ions that contain four coordinate bonds make?
TETRAHEDRAL SHAPE
40
What shape do complex ions that contain two coordinate bonds make?
LINEAR SHAPE
41
What shape do four coordinate bonds make in some cases?
SQUARE PLANAR.
42
What is haemoglobin?
A protein found in blood that helps to transport oxygen around the body.
43
What does haemoglobin contain?
Fe2+ ions, which are hexa-coordinated- six lone pairs are donated to them to form six coordinate bonds.
Four of the lone pairs come from nitrogen atoms, which form a circle around the Fe2+.
This part of the molecule is called HAEM.
The molecule that the four nitrogen atoms are part of is a multidentate ligand called porphyrin.
A protein called a globin and either an oxygen or a water molecule also bind to the Fe2+ ion to form an octahedral structure.
44
How does chromium most commonly exist?
In the 3+ or +6 oxidation state.
It can exist in the +2 oxidation state as well, but much less stable.
45
What two ions can chromium form in the +6 oxidation state?
Chromate (VI) ions (CrO4^2-) YELLOW
and
dichromate(VI) ions (CrO7^2-) ORANGE
46
Why are chromate (VI) and dichromate (VI) ions good oxidising agents?
They can easily be reduced to Cr^3+.
47
What colour are Cr^3+ ions when they are surrounded by 6 water ligands?
VIOLET
| but the water ligands are often substituted, so this solution usually looks green instead.
48
When an alkali (OH- ions) is added to aqueous dichromate(VI) ions (CrO7^2-) what is the colour change?Why?
ORANGE----->YELLOW
because aqueous chromate (VI) (CrO4^2-) ions are formed.
CrO7^2- (aq) + OH- (aq) -> 2CrO4^2- (aq) + H+ (aq)
49
When an acid (H+ ions) is added to aqueous chromate (VI) ions, what is the colour change? Why?
```
YELLOW----> ORANGE
aqueous dichromate (VI) ions form.
```
2CrO4^2- (aq) + H+ (aq) ----> Cr2O7^2- (aq) + OH- (aq)
opposite to when alkali is added to aqueous dichromate the two ions exist in equilibrium
CrO7^2- +H2O 2CrO4^2- +2H+
50
What does the position of the equilibrium between chromate ions and dichromate ions depend on?
pH- if H+ ions are added, the equilibrium shift to the left so orange CrO7^2- ions are formed. If OH- ions are added, H+ ions are removed and the equilibrium shifts to the right, forming yellow CrO4^2- ions.
51
What can dichromate ions be reduced using?
A good reducing agent, such as zinc and dilute acid.
52
Equation for reduction of dichromate ions using zinc and dilute acid. (colours)
Cr2O7^2-(aq) + 14H+(aq) + 3Zn(s) --> 3Zn^2+ (aq) +2Cr^3+ (aq) +7H2O
Cr2O7^2- is ORANGE
2Cr3+ is GREEN
53
What can zinc further reduce Cr3+ to? Equation.
Cr2+
2Cr3+ (aq) + Zn(s) ---> Zn2+ (aq) + 2Cr2+ (aq)
Cr3+ is GREEN
Cr2+ is BLUE
54
What do you need to reduce Cr3+ to Cr2+?
INERT ATMOSPHERE because Cr2+ is so unstable that it oxidises straight back to Cr3+ in air.
55
What do you use to oxidise Cr3+ to chromate (VI) ions? Equation.
HYDROGEN PEROXIDE in an ALKALINE SOLUTION
H2O2
2Cr^3+ + 10OH- +3H2O2 ---> 2CrO4^2- + 8H2O
Cr3+ is GREEN
C4O4^2- is YELLOW
56
What two oxidation states does cobalt exist?
+2 as Co^2+
+3 as Co^3+
It prefers to be in +2 state.
57
What are the two ways you can oxidise cobalt? Equations and colours.
1: Co3+ can be made by oxidising Co2+ with hydrogen peroxide in alkaline solution.
2Co2+ + H2O2 ---> 2Co3+ + 2OH-
2: You can oxidise Co2+ with air in ammoniacal solution.
PINK [Co(H2O)6]2+ ions, if you add a small amount of NH3 to this solution:
[Co(H2O)6]2+ + 2NH3 ---> [Co(H2O)4(OH)2] +2NH4+
[Co(H2O)4(OH)2] is a blue precipitate.
58
What can [Co(H2O)4(OH)2] be written as?
Co(OH)2
59
What happens when you add excess ammonia to the solution of [Co(H2O)4(OH)2]?
[Co(NH3)6}2+ ions form, producing a STRAW COLOURED solution.
60
What happens when [Co(NH3)6}2+ are left to stand in air?
Oxidised to [Co(NH3)6]3+ DARK BROWN
61
What colour is [Co(H2O)6]2+?
PINK
62
What colour is [Co(H2O)4(OH)2]?
BLUE
63
What colour is [Co(NH3)6]2+?
STRAW COLOURED
64
What is [Co(NH3)6]3+?
DARK BROWN
65
Describe the titration reaction of Fe2+ ions with Manganate (VII) ions (MnO4-).
Manganate (VII) ions (MnO4-) in aqueous potassium manganate (VII) (KMnO4). The solution turns purple at the end point.
MnO4- +8H+ + 5Fe2+ ---> Mn2+ +4H2O +5Fe3+
66
Describe the titration reaction of Fe2+ ions with dichromate (VI) ions (Cr2O7^2-).
dichromate (VI) ions (Cr2O7^2-) in aqueous potassium dichromate (VI) (K2Cr2O7). The solution turns orange at the end point.
Cr2O7^2- + 14H+ +6Fe2+ --> 2Cr3+ + 7H2O + 6Fe3+
67
Why do transition metals and their compound make good catalysts?
They can change oxidation states by gaining or losing electrons within their d-orbitals.
This means they can transfer electrons to speed up reactions.
68
What is the CONTACT PROCESS?
Used industrially to make sulphuric acid.
SO2(g) + 0.5O2 --V2O5 catalyst--> SO3 (g)
69
Describe the two steps of vanadium catalysing the contact process.
1: Vanadium (V) oxidises SO2 to SO3 and is reduced itself to vanadium (IV):
V2O5 + SO2 --> V2O4 + SO3
2: The reduced catalyst is then oxidised by oxygen gas back to its original state:
V2O4 + 0.5O2 ---> V2O5
70
Why is vanadium oxide able to oxidise SO2 to SO3?
It can be reduced to vanadium (IV) oxide. It's then oxidised back to vanadium (V) oxide.
It's then oxidised back to vanadium (V) oxide by oxygen ready to start again.
71
HETEROGENEOUS CATALYST
A catalyst that is in a different phase from the reactants.
| i.e. in a different physical state.
72
Give 3 examples of heterogeneous catalysts. Equations.
1. Iron, which is used in the Haber process for making ammonia.
N2(g) + 3H2(g) ----Fe catalyst----> 2NH3(g)
2. Vanadium (V) oxide that's used in the Contact Process:
SO2(g) + 0.5O2(g) --V2O5 catalyst---> SO3(g)
3. Chromium (III) oxide, which is used to manufacture methanol from carbon monoxide (CO) and hydrogen:
CO(g) + 2H2(g) ---CrO3(s) catalyst--> CH2OH(g)
CATALYST A SOLID, REACTANTS GASES
73
Where does the reaction occur when a heterogeneous catalyst is used?
On the surface of the catalyst
74
What does increasing the surface area of the catalyst do?
Increases the number of molecules that can react at the same time, increasing the rate of reaction.
75
What is used to make the area of the catalyst as large as possible?
A support medium
76
Describe catalytic converters.
Clean up emissions from car engines.
| They contain a ceramic lattice coated with a thin layer of rhodium.
77
What does the rhodium act as in a catalytic converter?
Acts as a catalyst helping to convert the bad waste gases to less harmful products.
78
What is a reaction that occurs in a catalytic converter?
2CO(g) + 2NO(g) --Rh catalyst---> 2CO2 (g) + N2 (g)
79
What are the benefits of a catalytic converter?
The lattice structure maximises the surface are of the catalyst, making it more effective.
Minimises the cost of the catalyst because only a thin coating is needed.
80
CATALYTIC POISONING
During a reaction, reactants are absorbed onto active sites on the surface of heterogeneous catalysts.
Impurities in the reaction mixture may also bind to the catalyst's surface and block reactants from being absorbed.
81
What does catalytic poisoning do?
Reduces the surface area of the catalyst available to the reactants, slowing down the reaction.
It also increases the cost of a chemical process because less product can be made in a certain time or with a certain amount of energy.
The catalysts may even need replacing or regenerating.
82
How does lead poison the catalyst in catalytic converters?
Catalytic converters reduce harmful emissions from car engines. Lead can coat the surface of the catalyst in a catalytic converter, so vehicles that have them fitted must only be run on unleaded petrol.
83
How does sulphur poison the iron catalyst in the Haber process?
The hydrogen in the Haber process is produced from methane.
The methane is obtained from natural gas, which contains impurities, including sulphur compounds. Any sulphur that is not removed is adsorbed onto the iron, forming iron sulphide, and stopping the iron from catalysing the reaction efficiently.
84
How can catalyst poisoning be reduced?
By purifying the reactants. This removes many of the impurities which would otherwise poison the catalyst.
85
ADSORB
Stuck on surface.
86
Why does catalytic poisoning only a problem for heterogeneous catalysts?
Homogeneous catalysts aren't affected because the reaction doesn't happen at the surface.
87
HOMOGENEOUS CATALYSTS
In the same physical state as the reactants.
| Usually an aqueous catalyst for a reaction between two aqueous solutions.
88
How does a homogeneous catalyst work?
By forming an intermediate species.
The reactants combine with the catalyst to make an intermediate species, which then reacts to form the products and reform the catalyst.
89
What causes the enthalpy profile for a homogeneously catalysed reaction to have two humps?
Two reactions- first intermediate species formed when reactants combined with catalyst.
Then this reacts to form the products and reform the catalyst.
90
CATALYST
A substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction.
91
Describe the redox reaction between iodide ions and peroxodisulphate (S2O8^2-).
The redox reaction between iodide ions and peroxodisulphate (S2O8^2-):
S2O8^2- (aq) + 2I- (aq) ---> I2(aq) + 2SO4^2- (aq)
92
Why does the redox reaction between iodide ions and peroxodisulphate occur slowly?
Both ions are negatively charged.
| The ions repel each other, so it's unlikely they'll collide and react.
93
Describe how iron acts as a catalyst for the reaction between S2O8^2- and I-.
Fe2+ ions are oxidised to Fe3+ ions by the S2O8^2- ions:
S2O8^2- (aq) + 2Fe2+ (aq) ---> 2Fe3+ (aq) + 2SO4^2-(aq)
The newly formed intermediate Fe3+ ions now easily oxidise the I- ions to iodine, and the catalyst is regenerated:
2Fe3+ (aq) + 2I- (aq) ---> I2 (aq) + 2Fe2+ (aq)
94
How do you test for iodine?
Adding starch solution- turns blue black.
95
AUTOCATALYSIS
When the product of the reaction and acts as a catalyst for the reaction. This means that as the reaction progresses and the amount of the product increases, the reaction speeds up.
96
Autocatalysis reaction between C2O4^2- and MnO4-. Equations.
2MnO4- (aq) + 16H+ (aq) + 5C2O4^2- ---> 2Mn2+ (aq) + 8H2O (l) + 10CO2 (g)
The product Mn2+ acts as the catalyst. .
This reacts with MnO4- to make Mn3+ ions:
4Mn2+ (aq) + MnO4-(aq) + 8H+(aq) ---> 5Mn3+(aq) + 4H2O(l)
The Mn3+ ions are intermediate. They then react with the C2O4^2- ions to make CO2 and reform Mn2+ catalyst:
2Mn3+ + C2O4^2- ---> 2Mn2+ +2CO2
97
Why is the reaction between C2O4^2- and MnO4- slow at the beginning.
The product Mn2+ acts as the catalyst, as there isn't much at start the rate of reaction the rate of reaction is slow.
98
Why is the activation energy at the start of the reaction between C2O4^2- and MnO4- high?
Uncatalysed.
| The reaction proceeds via the collision of negative ions, which requires a lot of energy to achieve.
99
Describe conc. time graph for a reaction where autocatalysis takes place.
High conc. during uncatalysed part of reaction, conc. decreases and rate of reaction increases (steeper curve) as conc. of catalyst increases. Graph levels off as MnO4- is used up.
100
How do ligands split the 3d subshell into two energy levels?
Normally the 3d orbitals of transition element ions all have the same energy. But when ligands bond to the ions, some of the orbitals are given more energy than others. This splits the 3d orbitals into two different energy levels.
Electrons tend to occupy the lower orbitals (ground state). To jump up to a higher orbital (excited states) they need energy equal to the energy gap, ΔE.
101
Where do electrons get the energy to jump to a higher energy level?
visible light
102
How can the energy absorbed when electrons jump up be worked out?
ΔE=hv
v=frequency of light absorbed (hertz/Hz)
h=Planck's constant (6.63x10-34Js)
103
What does the amount of energy needed to make electrons jump depend on?
The central metal ion an its oxidation state, the ligands and the coordination number, as these affect the size of the energy gap.
104
What happens when visible light hits a transition metal ion?
some frequencies are absorbed when electrons jump up to higher orbitals. The frequencies absorbed depend on the size of the energy gap.
The rest of the frequencies are reflected. These reflected frequencies combine to make the complement of the colour of the absorbed frequencies- colour you see.
105
What happens when visible light hits a transition metal ion?
some frequencies are absorbed when electrons jump up to higher orbitals. The frequencies absorbed depend on the size of the energy gap.
The rest of the frequencies are reflected. These reflected frequencies combine to make the complement of the colour of the absorbed frequencies- colour you see.
106
What happens if there are no 3d electrons or the 3d subshell is full?
No electrons will jump, so no energy will be absorbed. if there's no energy absorbed, the compound will look white or colourless.
107
Describe how spectrometry is used to find concentrations of transition metal ions.
by measuring how much light it absorbs.
1. White light is shone through a filter, which is chosen to only let the colour of light through that is absorbed by the sample.
2. The light then passes through the sample to a colorimeter, which calculates how much light was absorbed by the sample.
3. The more concentrated a coloured solution is, the more light it will absorb. So you can use this measurement to work out the concentration of a solution of transition metal ions.
108
What do you have to do before you find the unknown concentration of a sample?
produce a calibration graph.
This involves measuring the absorbances of known concentrations of the solution and plotting the results on the graph.
You can then measure the absorbance of your sample and reads its conc of the graph.
109
Describe the titration using manganate (VII) and iron.
ACIDIFIED POTASSIUM MANGANATE (VII), KMnO4, can act as an oxidising agent in redox titrations.
MnO4-(aq) + 8H+(aq) +5e- --> Mn2+(aq) +4H2O(l)
The hydrogen ions are usually supplied by adding dilute sulfuric acid.
```
Oxidises iron(II) to iron(III):
Fe2+(aq) ----> Fe3+(aq) + e-
```
COMBINED:
MnO4- + 8H+ + 5Fe2+ ------> Mn2+ + 4H2O + 5Fe3+
in a typical titration, aqueous potassium manganate (VII) is added from a burette to aqueous iron (II) ions in a conical flask.
The reaction is SELF INDICATING.
Aqueous manganate is DEEP PURPLE but aqueous manganese (II) is very PALE PINK.
It is essentially colourless in the concs. for titrations.
Manganate (VII) loses its colour as it enters the iron (II) solution.
The end point is when the permanent pink tinge caused by excess manganag (VII) first appears.
110
Equations involved in the titration involving manganate and iron?
MnO4-(aq) + 8H+(aq) + 5e- ----> Mn2+(aq) + 4H2O (l)
Fe2+(aq) -----> Fe3+(aq) + e-
111
Describe titrations involving dichromate and iron.
Acidified aqueous potassium dichromate (VI), K2Cr2O7, acts as an oxidizing agent in redox titrations:
Cr2O7^2-(aq) 14H+(aq) +6e- ----> 2Cr3+(aq) + 7H2O(l)
The hydrogen ions are usually supplied by adding dilute sulfuric acid or dilute hydrochloric acid.
COMBINED:
Cr2O7^2- + 14H+ + 6Fe2+ ---> 2Cr3+ +7H2O + 6Fe3+
Aqueous dichromate (VI) is orange but aqueous chromium (III) is green.
In principle the reaction could be self indicating, with an end-point when the mixture in the flask changes from green to orange.
BUT
in practice this is difficult to see and an indicator is used.
e.g. barium diphenylamine-4-sulfonate turns violet-blue in the presence of potassiu dichromate(VI) solution.
112
What are the names of ligands in a complex? (water, ammonia, chloride, hydroxide, cyanide)
```
AQUA
AMMINE
CHLORO
HYDROXO
CYANO
```
113
What are the names of chromium, cobalt, copper, iron, manganese, nickel, silver and vanadium in anionic compounds?
```
CHROMATE
COBALTATE
CUPRATE
FERRATE
MANGANATE
NICKELATE
ARGENTATE
VANADATE
```
114
Shapes and bond angles of different electron pair numbers.
```
2 LP, linear, 180
3 LP, trigonal planar, 120
4 LP, tetrahedral, 109.5
5 LP, trigonal bipyramidal, 90 and 120
6 LP, octahedral, 90
```
115
What is an example of a molecule that is square planar?
[Ni(CN)4]2-
116
What is an example of a molecule that is tetrahedral?
[CuCl4]2-
117
Cisplatin
complex- diamminechloroplatinum (II)
[PtCl2(NH3)2]
Square planar
118
What are the two stereoisomers of diamminedichloroplatinum(II)?
- cis- indicates that the two ammine ligands are next to each other. (cisplatin)
- trans- indicated that the two ammine ligands are on opposite sides.
119
What is cisplatin used for?
Used as an anticancer drug. Trans isomer does not have anticancer properties.
Used to treat many types of cancer- testes, ovaries, bladder, stomach, and lungs.
120
What are the side effects of cisplatin?
Side effects:Nausea, vomiting, allergic reactions, hearing loss. and kidney problems.
The risk of these side effects is greater at higher doses and it increases as the total amount of cisplatin used increases over time.
121
What else can form coordinate bonds with the iron (II) in haem other than oxygen?
Carbon monoxide.
Forms bonds that are less easily broken than those formed by oxygen, so it reduces the capacity of the blood to carry oxygen.
Makes CO toxic.
122
When is carbon monoxide formed?
Incomplete combustion of fuels
| it is important that the gas fires and boilers have adequate ventilation to ensure complete combustion
123
What colours do we see?
A substance appears coloured if it absorbs some of the colours in white light. The colours we see are complementary colours, the colours remaining after absorption of the colours by a substance.
