Transition metals 3.2.5 Flashcards
1
Q
what are the characteristics of transition metals because of their incomplete d sub shell
A
- Formation of coloured ions
- Variable oxidation states
- Catalytic activity
- Complex ion formation
2
Q
why is Zn not a transition metal
A
Zn can only form a 2+ ion. In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its ions
3
Q
Why is Sc not a transition metal
A
Sc can only form a 3+ ion. In this ion the Sc3+ has an empty d orbital and so does not meet the criteria of having an incomplete d orbital in one of its ions
4
Q
what’s the electron configuration of Zn
A
1s2 2s2 2p6 3s2 3p6 4s2 3d10
5
Q
what’s the electron configuration of Zn2+
A
1s2 2s2 2p6 3s2 3p6 4s0 3d10
6
Q
what’s the electron configuration of Sc3+
A
1s2 2s2 2p6 3s2 3p6 4s0 3d0
7
Q
what’s the electron configuration of Sc
A
1s2 2s2 2p6 3s2 3p6 4s2 3d1
8
Q
what do you have to do when working out the electron configuration of transition metal ions
A
When forming ions lose 4s before 3d
9
Q
why do transition metals have variable oxidation states
A
This is because the electrons sit in 4s and 3d energy levels which are very close to
10
Q
what is a complex
A
is a central metal ion surrounded by ligands
11
Q
what is a ligand
A
An atom , ion or molecule which can donate a lone electron pair
12
Q
what is coordinate bonding
A
When the shared pair of electrons in the covalent bond come from only one of the bonding atoms
13
Q
what is co ordination number
A
The number of coordinate bonds formed to a central metal ion
14
Q
what is a unidentate ligand
A
can form one coordinate bond per ligand eg. H2O , NH3 and Cl-
15
Q
what is a bidentate ligand
A
Have two atoms with lone pairs and can form two coordinate bonds per ligand e.g NH2CH2CH2NH2 , ethanedioate ion , C2O4- , ethane-1,2-diamine
16
Q
what is multidentate ligand
A
Can form 6 coordinate bonds per ligand e.g. EDTA4-
17
Q
what is the shape dependent on
A
The size of the ligands and the coordination number
18
Q
what shape does a complex with a coordination number of 6 form and what’s the bond angle
A
an octahedral shape
90 degrees
19
Q
how many NH3 and H20 ligands can fit around a central metal ion
A
6 because they’re smaller in shape
20
Q
how many Cl- ligands can you fit around a central metal ion
A
4 because they’re larger
21
Q
How many ethanedioate and ethane - 1,2-diamine ligands can you fit around a central metal ion
A
3 because they’re large
22
Q
what shape are complexes with a coordination number of 4 form and the bone angle
A
Tetrahedral
109.5 degrees
Square planar
90
23
Q
what’s a specific example of a square planar complex
A
Cis-platin
Pt as central metal ion
2 Cl ligands around it
2 NH3 ligands around it
24
Q
what shape does a complex with a coordination number of 2 have and the bond angle
A
Linear
180 degrees
25
what’s the specific example of a linear shape
[Ag(NH3)2]+
Tollens reagent
26
how do you work out the total oxidation state of the metal
Total oxidation state of the complex - total oxidation state of the ligands
27
what is haem
A multidentate ligand that is found in the molecule haemoglobin
28
what’s the shape of haemoglobin
Tetrahedral
29
How does haemoglobin transport oxygen
-oxygen substitutes the water ligand in the lungs where oxygen conc is high to form oxyhemoglobin which is then transported around the body
- Oxyhaemoglobin gives up oxygen to a place where it’s needed. Water takes the place and haemoglobin returns back to the lungs to start the process again
30
what happens when carbon monoxide is inhaled
The water ligand is replaced with a carbon monoxide ligand
carbon monoxide bonds strongly so it’s not readily replaced by oxygen or water
31
how do you know if you have a trans isomer
if the 2 different ligands are opposite each other
32
how do you know if you have a cis isomer
If the 2 different ligands are adjacent to each other
33
what is cisplatin
It’s used as an anti cancer drug
Platin binds to DNA of cancer cells and stops cancer dividing .
It can also prevent the replication of healthy cells by binding on to healthy DNA which may lead to unwanted side effects like hair loss
34
when does the d sub shell split into 2
When ligands bond with the central metal ion
35
what happens when the d sub shell is split into 2
An energy gap is created
When electrons absorb light energy some move from the lowest energy level ( ground state ) to higher energy level orbitals ( excited state)
36
in order for the d subshell to enter a higher energy level what must happen
The energy from the light must equal delta E
37
what is the size of delta E dependent on
•The central metal ion and its oxidation state
• the type of ligand
• the coordination number
38
what’s the equation to work out energy absorbed by the electrons
delta E = hc / wavelength of light absorbed
h= plancks constant
c= speed of light
39
what does the frequency of visible light absorbed by transition metal complexes depend on
The size of delta E
- the large the energy gap of delta E the higher the frequency of light absorbed
40
what happens if any frequencies which are not absorbed
They are reflected or transmitted
41
what’s the colour of the complexes where we have a full 3d or empty 3d subshell
Colourless or white
- No electrons can migrate to the higher energy level
42
when does ligand substitution happen
the coordination number changes and so does the shape .
normally happens when a smaller ligand is substituted by a larger ligand
43
what has an impact on the colour
The coordination number
The oxidation state
changing a ligand
- this will alter the energy split between the d orbitals , changing energy hence the frequency of light absorbed
44
what is colorimetry used to measure
the concentration of transition metal ions in solution
45
what’s the reaction for a copper complex ion reacting with excess ammonia
[Cu(H20)6]2+ (aq) + 4NH3(aq) => [Cu(NH3)4(H2O)2] 2+ + 4H2O
46
what’s the reaction of cobalt complex ion reacting with chlorine
[Co(H20)6]2+(aq) + 4Cl-(aq) => [CoCl4] 2- (aq) + 6H2O(l)
47
what’s the reaction between copper complex ion and chlorine
[Cu(H20)6]2+(aq) + 4Cl-(aq) => [CuCl4] 2- (aq) + 6H2O(l)
48
what’s the reaction between iron complex ion and chlorine
[Fe(H20)6]3+(aq) + 4Cl-(aq) => [FeCl4]- (aq) + 6H2O(l)
49
which ligands are more stable
Multidentate ligands are more stable than moderate ligands
50
when are the bonds broken and formed in a ligand substitution reaction
Bonds are broken in the original complex and new ones are formed to make the new complex
51
what is the chelate effect
the increase in stability .
When we substitute monodentate ligands with bidentate ligands and multidentate ligands we create a solution with more particles in it . This means we have an increase in entropy => more likely
to happen
52
what’s the colour of the 4 vanadium ions , v2+ , V3+ , VO2+ and Vo2 +
V2+
Violet
V3+
Green
VO2+
Blue
Vo2 +
yellow
53
what’s the reaction for Vo2+ reduced to VO 2+
2Vo2 + (aq)+ Zn(s) + 4H+(aq) => 2VO2+ (aq) + Zn2+(aq) + 2H2O(l)
yellow to blue
54
what’s the reaction of VO2+ reduced to V3+
2VO2+ (aq) + Zn(s). + 4H+ (aq) => 2V3+ (aq) + Zn2+(aq) + 2H2O(l)
Blue to green
55
what’s the reaction of V3+ reduced to V2+
2V3+(aq) + Zn(s) => 2V2+(aq) + Zn2+(aq)
Green to violet
56
what is used to reduce vanadium ions
zinc (zn)
57
what does redox potentials tell us
How easily an ion is reduced
58
what type of ions have the largest redox potentials
The least stable have the largest redox potentials and are likely to be reduced
59
why might there be a difference in redox potentials to the standard values seen in a data book
Dependent on the environment the ions are in
Standard conditions :
100kPa
298K
1moldm-3
60
what affects the redox potential
- ligand
- pH ( more acidic the solution is the larger the redox potential - more likely to be reduced )
61
what’s the reaction for the oxidation of Fe3+ to Fe2+
MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) => Mn2+ (aq) + 4H2O(l) + 5Fe3+(aq)
purple => colourless
62
what’s the reaction for reducing Fe3+ to Fe2+
2Fe3+(aq) + 2I-(aq) => I2(aq) + 2Fe2+(aq)
63
what’s the reaction for reducing Cr3+ to Cr2+
Cr2O72- + 14H+ + 6Fe2* => 2Cr3+ + 7H2O + 6Fe3+
Orange to green
64
what is a heterogenous catalyst
Catalyst that is in a different phase from the reactants .
The catalyst is one different state to the reactants
65
what’s an example of a heterogeneous catalyst
The haber process :
N2 + 3H2 => 2NH3
A solid iron catalyst is used
66
what increases the rate of reaction of a heterogenous catalyst
increasing the surface area of a heterogeneous catalyst increases the rate of reaction
67
what’s a homogenous catalyst
catalyst that’s in the same phase as the reactants.
They form intermediate species by reactants combining with the catalyst which react to form products
Catalyst is reformed again
68
what is the contact process
uses vanadium (V) ( V2O5) to make sulfuric acid ( SO2 to SO3)
69
what are the reactions of the contact process
1) V2O5 + SO2 => V2O4 + SO3
2) V2O4 + 1/2O2 => V2O5
70
what kind of catalysts are used in the contact process
heterogenous catalyst
71
what’s a problem with using heterogeneous catalysts
Can be poisoned by impurities :
Impurities can bind to the surface of a catalyst and can block active sites for reactants to adsorb.
When an impurity blocks a site it’s called poisioning
Catalytic poisoning reduced the surface area of the catalyst for the reactants to add on to.
This slows down the reaction
72
what does a poisoned catalyst mean
- less product is made
- the catalyst needs to be replaced or cleaned more often
- increased cost of all chemical process
73
how many activation energies does a homogenous catalyst have
2
74
what’s an example of using homogeneous catalysts
Fe2+ oxidised to Fe3+
S2O8 reduced to SO42-
75
how do we speed up reactions using a homogeneous catalyst
lowering the activation energy
76
what is autocatalysis
another form of homogenous catalysis where the product catalysises the reaction
77
what is an example of autocatalysis
where Mn2+ is the catalyst in a reaction between C2O42- and MnO4-
78
EQ : state the meaning of the term transition metal complex (1)
metal atom / ion surrounded by ligands
79
EQ : why is this reaction slow before catalyst is added
Two negative ions repel so activation energy is high
80
what is the electron configuration of an atom of a transition metal
4s2 3d8
81
Give two equations to show how Fe2+ ions catalyse S2O8 2- + 2I- => 2SO4 2- + I2
2 Fe3+ + 2I- => I2 + 2 Fe 2+
2 Fe 2+ + S2O8 2- => 2SO4 2- + 2 Fe3+
82
EQ : pt acts as a heterogeneous catalyst in reaction between ammonia and oxygen . It provides an alternative reaction route with a lower activation energy . Describe the stages of this alternative route (3)
- reactants adsorb onto surface of platinum
- bond breaks / weakens
- desorption of product
83
what’s the reaction of NH3 with O2 to form N2O
2NH3 + 2O2 => N2O + 3H2O
84
How does optical isomerism arise in an octahedral complex
- they can only form when specific bidentate ligands are bonded e.g
Ethanediote ( C2O4)2-
Ethane-1,2-diamine (NH2CH2CH2NH2)
85
EQ : Transition metal complexes have different shapes and many show isomerism . Describe the different shapes of complexes and show how they lead to different types of isomerism. Use examples of complexes of cobalt (II) and platinum (II) You should draw the structures of the examples chosen (6)
- transition metal complexes can form octahedral, tetrahedral and square planar
- Draw octahedral structure with Co as central metal ions and NH3 or H2O monodenate ligands surrounding it
- Draw tetrahedral complex of Co metal in the middle and Cl bidentate ligands around it
- draw Cisplatin molecule for square planar ( Pt in the middle , 2Cl ligands , 2 NH3 ligands
- octahedral and square planar complexes can exhibit e/z isomerism depending on the 3D orientation of the bonded ligands
- Draw E/Z isomerism of octahedral and Square planar
- Opticsk isomerism is in octahedral complexes => non superimposable mirror images of one another
- These can only form when specific bidentate ligands are bonded e.g ethanediote and ethane-1,2-diaminr
- draw optical isomerism with Co as central metal ion and ethanediote around it
86
what’s the overall equation for the reaction between iodide and persulphste ions in homogeneous catalysis
S2O8 2- + 2I- => 2SO42- + I2
87
why is the reaction between iodide and persulphste ions slow before Fe3+ is used as a catalyst for homogenous catalysis
- the reaction needs a collision between two negative ions
- repulsion between ions is going to hinder this meaning high activation energy
When Fe3+ is added it attracts the S2O8 2- so lowers the activation energy .
Iron has a variable oxidation state or Fe 2+ is oxidised to Fe 3+
88
what type of heterogeneous catalyst is used in the manufacture of methanol from carbon monoxide and hydrogen and the equation for this
Cr2O3
CO + 2H2 => CH3OH
89
what’s important to check for the reactants if poisoning can occur
the purity of the reactants
90
what are the cost implications of catalytic poisoning in the haber process
Poisoning by sulphur in the haber process and by lead in catalytic converters in cars means that catalysts lose their efficiency and may need to be replaced
91
why can’t leaded petrol be used in cars fitted with a catalytic converter
lead strongly adsorbs onto the surface of the catalyst
92
what are the steps in heterogeneous catalysis
1) reactants form bonds with atoms at active sites on the surface of the catalyst ( adsorbed onto the surface )
2) as a result bonds in the reactants are weakened and break
3) new bonds form between the reactants held close together on catalyst surface
4) this in turn weakens bonds between product and catalyst and product leaves ( desorbs)
93
what helps to determine the effectiveness of catalytic activity
Strength of the adsorption :
some metals have too strong adsorption so products can’t be released
some metals have too weak adsorption and the reactants do not adsorb in high enough conc
Ni and Pt have about the right strength and are the most useful as catalysts
94
what will improve the effectiveness of a solid catalyst
Increasing the surface area .
A support medium is often used to maximise the surface area and minimise the cost
95
what’s en equation that links colour and frequency of light absorbed with the energy difference between the split d orbitals
E = hv
v = frequency of light absorbed
h = plancks constant
E = energy different between split orbitals
96
when does partial substitution of ethanedioate ions occur
When dilute aq solution containing ethanedioate ions is added to a solution containing aq copper (II) ions . In this reaction 4 water molecules are replaced and a new complex is formed
Cu (H2O)6 2+ + 2C2O42- => [Cu(C2O4)2(H2O)2] 2- + 4H2O
97
what are some equations to show formation of bidentate complexes
M(H2O)6 2+ + 3NH2CH2CH2NH2 => [M(NH2CH2CH2NH2)3] 2+ + 6H2O
M(H2O)6 2+ + 3C2O4 2- => [M(C2O4)3] 4- + 6H2O
98
EQ : when cisplatin bonds to DNA , which is the correct ligand replacement reaction (1)
Replacement of two Cl- ligands
99
what’s the electron configuration for copper
[Ar] 3d4 4s2
100
what’s the electron configuration for chromium
[Ar] 3d5 4s1
101
Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of [CoCl4]2- ion (1)
Too many electrons in d orbital
102
EQ : an acidified solution of NH4VO3 reacts with zinc.
Explain how observations from this reaction show that vanadium exists in at least 2 different oxidation states (2)
- Two different colours of solution are observed
- Because each colour is due to vanadium in a different oxidation state
103
EQ : a coordinate bond is formed when a transition metal ion reacts with a ligand . Explain how this coordinstr bond is formed (2)
-an electron pair on the ligand
- is donated from the ligand to the central metal ion
104
EQ : complex ion [Cu(NH3)4(H2O)2]2+ reacts with 1,2-diaminoethane to form [Cu(NH2Ch2CH2NH2)2(H2O)] 2+ .
Suggest why the enthalpy change for the reaction is approximately zero (2)
Explain why the reaction occurs despite having an enthalpy change that is approximately zero (2)
- Cu-N bonds formed have similar enthalpy to Cu -N bonds broken
- the same number of bonds broken and made
• 3 particles form 5 particles
• Disorder increases because more particles are formed / entropy increases
• therefore free energy change is negative
105
Explain how properties of Mn2+ enables it to act as a catalyst
- Mn can exist in variable oxidation states
- Ea lowered because oppositely charged ions attract
- 4Mn 2+ +8H+ +MnO4- => 5Mn 3+ + 4H2O
- 2 Mn3+ + C2O4 2- => 2CO2 + 2Mn2+
OR
Mn3+ reduced to Mn2+ by C2O42-
Mn2+ oxidised to Mn3+ by MnO4-
106
EQ : Sketch a graph to show how the conc of MnO4- ions varies with time in this autocatalysis reaction . Explain the shape of the graph (4)
- S shaped curve must not rise significantly and must not fall rapidly initially
- starts on conc axis and is levelling out
( s shaped going down )
• slope / rate increases as catalyst concentration forms
• slope / rate decreases as concentration of MnO4- ions / reactants decreases or reactants are being used up
107
EQ : Write an equation to show how the [Co(NH3)6]2+ ion reacts with 1,2 diaminoethane.
Explain the thermodynamic reasons why this reaction occurs . (5)
[Co(NH3)6]2+ + 3NH2CH2CH2NH2 => [Co(NH2CH2CH2NH2)3]2+ + 6NH3
- 4 particles form 7 particles
- disorder / entropy increases
- delta H is approximately zero
- Delta G is negative
108
EQ : explain with the aid of equations , how and why vanadium (V) oxide is used in the contact process (4)
V2O5 + SO2 => SO3 + V2O4
V2O4 + 1/2 O2 => V2O5
- acts as a catalyst
- speeds up overall reaction
109
EQ : The complex ion formed in aq solution between cobalt(II) ions and chloride ions is a diff colour from the [Co(H2O)6]2+ ion . State why these complex ions have diff colours (3)
- in different complexes , d orbitals will have different energies
- light is absorbed which excites electrons in the d orbital
- different wavelengths of light transmitted
