5. Transition Metals Flashcards
1
Q
What is a transition metal?
A
A metal in the central block of the periodic table that has an incomplete d sub-shell in at least one of its stable ions
2
Q
Why do transition elements form 2+ ions, and why do they have similar properties?
A
When ions are formed it is the 4s electrons that are lost first
3
Q
Why is Cu a transition metal?
A
For Cu 2+ [[Ar] 3d9] it has an incomplete d sub-shell
4
Q
Physical properties of transition metals?
A
- conduct heat and electricity
- malleable and ductile
- hard and strong
- dense
- high melting point
5
Q
Chemical properties of transition metals?
A
- can form complexes
- form coloured compounds
- have variable oxidation states
- can act as catalysts
6
Q
What is a ligand?
A
A molecule, atom or ion that has one or more lone pairs that it can donate to a central metal ion
7
Q
What are bidentate ligands?
A
Ligands that can donate 2 lone pairs of electrons
8
Q
What are monodentate ligands?
A
Ligands that can donate 1 lone pair of electrons
9
Q
Examples of monodentate ligands?
A
H2O, NH2, CN- and Cl-
10
Q
Examples of bidentate ligands?
A
- NH2CH2CH2NH2
* C₂O₄²⁻
11
Q
What are multidentate ligands?
A
Ligands that can donate more than two pairs of lone electrons
12
Q
Example of a multidentate ligand?
A
EDTA⁴⁻
13
Q
What is a complex?
A
A cenral metal ion surrounded by ligands
14
Q
What do ligands do in order for a complex to be formed?
A
Donate at least one pair of electrons to form a co-ordinate bond with the central ion
15
Q
What happens to transition metals in an aqueous solution?
A
They are always hydrated i.e. they form co-ordinate bonds with water molecules - water molecules can act as ligands
16
Q
What is formed when a transition metal is in an aqueous solution?
A
A hexaaqua ion
17
Q
What are hydrated complex ions also called?
A
Hexaaqua ions
18
Q
What is the coordination number?
A
The number of coordinate bonds formed by ligands around the central metal ion
19
Q
What must the coordination number not be confused with?
A
The number of ligands bonded
20
Q
What does the coordination number determine?
A
The shape of the complex
21
Q
What shape is formed if a complex has two coordinate bonds?
A
Linear
22
Q
What shape is formed if a complex has four coordinate bonds?
A
Tetrahedral or square planar
23
Q
What shape is formed if a complex has six coordinate bonds?
A
Octahedral
24
Q
What shape do complexes with Cl- ligands make?
A
Tetrahedral
25
What is the coordination number of octahedral complexes?
6
26
What are octahedral complexes commonly formed from?
Small ligands e.g. H2O and NH3
27
What type of isomerism can octahedral complexes display? And with what?
Cis-trans isomerism with monodentate ligands
28
Where are the ligands on a cis complex?
On the same side
29
Where are the ligands on a trans complex?
On opposite sides
30
When can octahedral complexes display optical isomerism?
When there are two or more bidentate ligands in the complex
31
When does optical isomerism occur?
When the two isomers (enantiomers) exist as two non-superimposable mirror images
32
What does a ligand substitution involve?
Breaking the coordinate bond between the transition metal and the ligand
33
How can the overall effect of ligand substitution on a molecule be determined?
The type of ligand needs to be determined
34
What types of ligand are there?
* monodentate
* bidentate
* multidentate
35
What is a monodenate ligand?
A ligand with one atom capable of donating a lone pair of electrons forming one coordinate bond
36
Examples of monodenate ligands?
H20, NH3 and CL=l-
37
What shape complex do H2O and NH3 form? Why is this?
Octahedral as they are small ligands that can form 6 bonds with the central metal ion
38
What shape complexes do Cl- form? Why is this?
Tetrahedral - repulsion between 6 Cl- is too great and only 4 bonds are formed with the central metal ion
39
What happens if a neutral ligand is replaced with a neutral ligand?
No change in shape, charge, or coordination number
40
What happens if a neutral ligand is replaced with Cl-?
Change in charge, coordination number and shape - octahedral to tetrahedral
41
What happens if a neutral ligand is replaced with CN-, EDTA4- or C2O4 2-?
Change in charge, no change in coordination number or shape
42
What should be noted about the formation of [Cu(NH3)4(H2O)2]2+ from (Cu(H2O)6)2+?
It is incomplete substitution, however all six H2O molecules could be replaced if the concentration of the ammonia solution is increased by carrying out the reaction in an ice cold saturated solution or in liquid ammonia
43
What can a change of the H2O ligand by Cl- involve?
A change in coordination number and charge on the complex
44
What is a bidentate ligand?
Ligands that have 2 atoms capable of donating an electron pair forming two coordinate bonds
45
Examples of bidentate ligands?
* 1,2-diaminoethane (NH2CH2CH2NH2)
| * ethanedivoate ions (C2O4 2-)
46
What is a multidentate ligand?
A ligand with a number of atoms capable of donating an electron pair producing several coordinate bonds
47
Examples of multidentate ligands?
* EDTA 4-
| * porphyrin (haem)
48
Example of what complex porphyrin is involved in?
Haemoglobin - with an Fe centre
49
What is haemoglobin?
An Fe2+ centre with porphyrin forming 6 coordinate bonds
50
What is the shape of haemoglobin?
Octahedral
51
How is oxygen transported in the blood?
Oxygen binds to haemaglobin
52
How many O2 molecules are attached to a fully saturated oxyhaemoglobin?
4
53
Why is carbon monoxide toxic?
It binds very strongly to haemoglobin; it replaces oxygen co-ordinately bonded to Fe(II)
54
What is the chelate effect?
When bi and multidentate ligands replace monodentate ligands from complexes
55
What type of ligands are known as chelating ligands?
Bi and multi
56
Why can multi dentate ligands be used to remove d-block metal ions from solution via a substitution reaction?
Due to the stability of the complex they form
57
Through what reaction do multi dentate ligands remove d-block metal ions from solution?
Substitution
58
What happens when mono dentate ligands are replaced with bidentate?
Makes complex more stable (chelate effect)
59
How can a complex be made more stable?
If a single ligand makes more bonds with the metal ion the more stable the complex will be
60
Why is the substitution of bi and multi dentate ligands difficult to reverse?
The product of both reactions are more stable than the reactant complex
61
How can the stability of complexes with chelating ligands be explained?
In terms of the increase in entropy of the system
62
What is the overall feasibility of the reaction involving chelating ligands determined using?
ΔG = ΔH - TΔS
63
In ΔG = ΔH - TΔS, what does G stand for?
Gibbs free energy
64
In ΔG = ΔH - TΔS, what does T stand for?
Temperature
65
In ΔG = ΔH - TΔS, what does S stand for?
Entropy
66
In ΔG = ΔH - TΔS, what does H stand for?
Enthalpy
67
In ΔG = ΔH - TΔS, what value must G take for the reaction to be feasible?
Negative
68
What is entropy?
Measure of disorder
69
In ΔG = ΔH - TΔS, what will the value of ΔH be?
Close to 0 as there is a similar type and number of bonds broken and formed
70
During ligand substitution, what does the entropy value depend on?
The number of particles moving freely in solution
71
Why is feasibility of ligand substitution largely due to change in entropy?
The number of bonds broken and formed are the same and therefore enthalpy change is usually very small, so feasibility is largely down to change in entropy
72
What does an increase in number of particles mean for entropy?
Increase in disorder, therefore entropy
73
What does an increase in number of particles mean for TΔS?
Makes it more negative therefore ΔG more -ve → therefore the feasible direction of the reaction and the product is more stable than the reactant complex
74
Can octahedral complexes display optical isomerism?
Yes, when there are two or more bidentate ligands in the complex
75
When can octahedral complexes display optical isomerism?
When there are two or more bidentate ligands in the complex
76
What is the coordination number of tetrahedral complexes?
4
77
What does it mean that a tetrahedral complex has a coordination number of 4?
The central metal ion forms 4 bonds
78
What are tetrahedral complexes commonly formed from?
Larger ligands e.g. Cl
79
What complexes adopt a square planar shape?
Some complexes with a coordination number of 4
80
What can square planar complexes display?
Cis-trans isomerism
81
Is cisplatin the cis or trans isomer?
Cis
82
What is a cis isomer?
When the same groups are on the same side of the central metal ion
83
What is a trans isomer?
When the same groups are on opposite sides of the central metal ion
84
What is the coordination of linear complexes?
2
85
What does it mean that the coordination number of linear complexes is 2?
The central metal ion forms 2 bonds
86
What are linear complexes commonly formed from?
The metal ion Ag+
87
What shape complex is Tollen's reagent?
Linear
88
What is the name for [Ag(NH3)2]?
Tollen's reagent
89
Is silver a transition metal?
No
90
What does the colour of a complex depend on?
* oxidation state of metal centre
* coordination number
* ligand
* the metal itself
91
Why are transition metals coloured?
* colour happens when some wavelengths of visible light absorbed
* this is due to the transfer of an electron between the orbitals in an unfilled d sub level
* transition metal atoms/ions have incomplete d sub level; all 5 orbitals in d sub level have same energy
* however in a complex ion the d orbitals move to 2 different energy levels due to the difference in overlapping with the ligands
* electrons excited by absorbed certain frequencies
* the light not absorbed is reflected and the complex appears this colour
92
When does colour arise?
When some wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected
93
What energy do the 5 orbitals in the d sub level have? Are there any exceptions to this?
They have same energy, however in a complex ion the d orbitals move to 2 different energy levels due to the difference in overlapping with the ligands
94
How can an electron be promoted from ground to excited state?
By absorbing certain frequencies of radiation from the visible light spectrum
95
Why, in a complex ion, do the d sub levels move to two different energy levels?
Due to the repulsion of ligands
96
How is the energy absorbed between two orbitals summarised?
ΔE = hv = hc/ƛ
97
Why might a species not appear to be coloured?
If there are no d electrons or if the d orbitals are full
98
What property can be used to identify transition metals?
The fact that each will absorb visible radiation of a different frequency and appear a different colour
99
What factors can change the energy of d orbitals and therefore the colour of transition metals?
* oxidation state of metal centre
* coordination number
* ligand
100
What colour is the complex [Co(H₂O)₆]²⁺?
Pink
101
What colour is the complex [Cu(H₂O)₆)²⁺?
Blue
102
What colour is the complex [Fe(H₂O)₆)²⁺?
Green
103
What colour is the complex [Fe(H₂O)₆)³⁺? Why might this not be the case?
Violet
| these solutions may appear different colours due to the presence of other complex ions which exist in equilibrium
104
What colour is the complex [Al(H₂O)₆)³⁺?
Colourless
105
Why is the complex [Al(H₂O)₆)³⁺ colourless?
It has a complete d sub level so it is not a transition metal, so electrons can't be excited
106
What does the amount of light absorbed by a transition metal solution depend on?
How many ions it interacts with
107
What does the wavelength of radiation absorbed by a transition metal depend on compared to the quantity of the radiation?
* wavelength depends of nature of ion
| * quantity of radiation absorbed depends on concentration of coloured solution and distance that light travels
108
What does the quantity of radiation absorbed by a transition metal solution depend on?
* concentration of coloured solution
| * distance that light travels
109
What does a spectrophotometer do?
Measures concentration of metal ions by measuring the absorbance of visible or UV radiation by a sample in a cell on unknown (fixed) path length and comparing it with measurements for standard solutions
110
What is a spectrophotometer also known as?
A colorimeter
111
How is the absorbance of radiation measured using a colorimeter?
1. sample placed in a cell in the spectrometer
2. visible spectrum scanned to find the most intense absorption frequency
3. range of single frequencies, each known as monochromatic light, is then passed through the sample one at a time and the absorbance is measured
4. absorbance spectrum is displayed as a spectrum or a printout of absorbance values at a particular wavelength
112
What graph is plotted in UV/visible spectrometry/colorimetry?
Calibration graph of concentration against absorbance
113
What is UV/visible spectrometry/colorimetry used for?
To find unknown concentration
114
What does the height of the peak on a wavelength-absorption graph depend on?
The concentration of the solution, and may be compared to standard charts
115
What is colorimetry?
A more simple technique than spectrometry, where light is passed through a filter to produce light of one colour - the filter is chosen to provide the colour of light which the sample will absorb most
116
What is the oxidation state of an element in a compound?
The hypothetical charge an atom in a compound would carry if the compound were 100% ionic
117
What is the oxidation state of a simple ion?
Charge on ion
118
What is the oxidation state of group 1 metals in a compound?
+1
119
What is the oxidation state of group 2 metals in a compound?
+2
120
What is the oxidation state of P block elements?
Variable
121
What is the oxidation state of fluorine in a compound?
-1
122
What is the oxidation state of chlorine in a compound (except with F and O)?
-1
123
What is the oxidation state of hydrogen in a compound (except ionic halides)?
+1
124
What is the oxidation state of oxygen in a compound (except peroxides and F2O)?
-2
125
What is the sum of oxidation states in a polyatomic ion?
Overall charge
126
What is the sum of oxidation states of all the elements in a compound?
0
127
Up to Mn ([Ar]3d54s2), what is the maximum oxidation state?
The total number of electrons in the 3d and 4s orbitals
128
What charge ions do transition metals form? Are there any exceptions to this?
2+ with the exception of Sc → 3+
129
Why is Sc³⁺ especially stable?
As it has a noble gas structure
130
When does the 2+ oxidation state of transition metals become more stable?
As the atomic number increases
131
Why does an increase in atomic number make the 2+ oxidation state more stable?
The increase in nuclear charge makes it more difficult to remove the d electrons
132
What can happen to a transition metal in a redox reaction?
Metal ion can be oxidised or reduced
133
How many oxidation states can Vanadium exist in solution?
4
134
How are the different oxidation states of Vanadium in solutions identified?
By the colour of the solution
135
In VO₂⁺, what is the oxidation state of Vanadium?
+5
136
In VO²⁺, what is the oxidation state of Vanadium?
+4
137
In V³⁺, what is the oxidation state of Vanadium?
+3
138
In V²⁺, what is the oxidation state of Vanadium?
+2
139
What is the colour of VO₂⁺?
Yellow
140
What is the colour of VO₂⁺?
Blue
141
What is the colour of V³⁺?
Green
142
What is the colour of V²⁺?
Violet
143
How to remember colours of Vanadium in compounds (decreasing oxidation states)?
You - yellow
Better - blue
Get - green
Vanadium - violet
144
How can Vanadium (V) be reduced through each oxidation state?
By zinc metal in acidic solution
145
What is the overall equation for the complete reduction of Vanadium (V)?
2VO₂⁺ + 3Zn + 8H⁺ → 2V²⁺ + 3Zn²⁺ + 4H₂O
146
How is the equation for the complete reduction of Vanadium derived (2VO₂⁺ + 3Zn + 8H⁺ → 2V²⁺ + 3Zn²⁺ + 4H₂O)?
* reduction: VO₂⁺ + 4H⁺ + 3e⁻ → V²⁺ + 2H₂O
| * oxidation: Zn → Zn²⁺ + 2e⁻
147
What is the formula for diammine silver (I)?
[Ag(NH₃)₂]⁺
148
Which is the active ion in Tollen's reagent?
Diammine silver (I)
149
How is diammine silver reduced to silver?
By oxidising aldehydes (but not ketones) to a carboxylate anion (in a carboxylic acid)
150
What does the redox potential of an atom or ion show?
How easy it is to be reduced to a lower oxidation state
151
What can redox potentials also be called?
Electrode potentials
152
What does it mean if an ion has a more positive value of redox potential?
The more likely the ion is to be reduced
153
When can redox potentials for the same reaction change?
When the conditions are changed
e.g. some ions need H+ ions to be present in order to be reduced, and others release OH- into the solution when they are reduced
154
What affects the size of the redox potential?
The conditions i.e. H+/OH- ions and pH
155
In what pHs will redox potential be more positive?
Acidic as the ion will be more easily reduced
156
What does a redox titration do?
Finds out how much oxidising agent is needed to react exactly with a given quantity of reducing agent (and vice versa)
157
Why are transition metals often found in oxidising and reducing agents?
They have variable oxidation states
158
Why are transition metals useful to find the end point during a titration?
The different colour of their varied oxidation state
159
In the two specific redox titration reactions required for a level, what happens to MnO₄⁻?
It is reduced to Mn²⁺ during a titration
160
What reducing agents are used in the reduction of MnO₄⁻?
Fe²⁺ and C₂O₄²⁻
161
What are the half equations and therefore overall equation for the reduction of MnO₄⁻ using Fe²⁺?
oxidation: 5Fe²⁺ → 5Fe³⁺ + 5e⁻
reduction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
overall: MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O
162
What is the reaction ratio for the reduction of MnO₄⁻ using Fe²⁺?
5:1
Fe:MnO₄
163
What are the half equations and therefore overall equation for the reduction of MnO₄⁻ using C₂O₄²⁻?
oxidation: 5C₂O₄²⁻ → 10CO₂ + 10e⁻
reduction: 2MnO₄⁻ + 16H⁺ + 10e⁻ → 2Mn²⁺ + 8H₂O
overall: 2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 10CO₂ + 8H₂O
164
What is the reaction ratio for the reduction of MnO₄⁻ using C₂O₄²⁻?
5:2
| C₂O₄²⁻:MnO₄⁻
165
What is the indicator in the reduction of MnO₄⁻?
None - self-indicating
166
What is the colour change at the end point in the reduction of MnO₄⁻?
Colourless to light pink
167
Why, in the reduction of MnO₄⁻, is the colour change at the end point colourless to light pink?
Due to the presence of the first drop of MnO₄⁻ in excess
168
Why does the MnO₄⁻ appear to be pale pink at one drop of excess in the redox titration?
It is largely diluted in solution
169
What is a suitable acid in the redox titration of MnO₄⁻?
Dilute H2SO4
170
What are unsuitable acids in the redox titration of MnO₄⁻, and why?
* conc H2SO4 (oxidises some of the Fe²⁺)
* conc HNO3 (oxidises some of the Fe²⁺)
˄lower titre
* HCl (is oxidised by MnO₄⁻ to form Cl₂)
* ethanoic acid (weak acid so not enough H⁺)
˄higher titre
171
In redox titrations, what usually goes in the burette?
The oxidising agent (i.e. MnO₄⁻ for A level examples)
172
What are catalysts?
Substances that speed up the rate of chemical reactions, without being chemically changed, by providing a route to lower Ea
173
Are transition metals used as catalysts?
Yes
174
How do catalysts provide a surface for reactions to occur?
By forming weak bonds to the reacting species, holding them in place
175
Why can transition metals catalyse certain redox reactions?
They can form more than one stable oxidation state and so can accept and lose electrons easily
176
What types of catalysts can transition metals behave as?
Heterogenous or homogenous
177
What is the main step in the manufacture of sulphuric acid?
The oxidation of sulphur dioxide to sulphur trioxide
178
What is the equation for the oxidation of sulphur dioxide to sulphur trioxide?
SO₂ + O₂ → 2SO₃
179
What is the process called in which V2O5 behaves as a catalyst in the manufacture of sulphuric acid?
The contact process
180
What reactions show V₂O₅ in the contact process?
1. 2V₂O₅ + 2SO₂ → 2V₂O₄ + 2SO₃
2. 2V₂O₄ + O₂ → 2V₂O₅
(overall equation is these two combined but without the V₂O₅ catalyst and the V₂O₄ intermediate)
181
What is the intermediate of V₂O₅ in the contact process?
V₂O₄
182
What are heterogeneous catalysts?
Those that are in a different phase to the reactants
183
Why are metals used in heterogeneous catalysis?
They are solid and in a different phase to the reactants
184
Where does heterogenous catalysis occur?
At the surface of the metal
185
How does a heterogenous catalyst work?
By allowing reactant molecules to bond to the surface of the metal, usually by attracting the surface electrons
186
What is the process where at least one of the reactants binds to the surface of the metal?
Adsorption
187
What does adsorption do?
Weakens bonds within reactant molecules
188
What are active sites?
Places on the surface where molecules are adsorbed
189
What can molecules do in an effective catalyst?
Move about the surface, bonding to different active sites
190
What happens in heterogenous catalysis when new products are made?
The products are desorbed from the surface to make way for new reactant molecules
191
How can the adsorption of reactants onto the surface result in increased reaction?
* bonds within reactant molecules are weakened, lowering Ea
* causes reactant molecules to break up into more reactive fragments, lowering Ea
* reactants are held in a position that will increase the chance of favourable collisions
* giving a higher conc of one reactant on the surface increasing the chance of favourable collisions
192
What happens if adsorption is too weak?
Not many molecules will be adsorbed so the catalyst will have very little effect
193
What happens if adsorption is too strong?
Molecules will not be able to move around the active sites, and so be less likely to meet another reactant so be less likely to react (also any product will tend to remain on the surface instead of being desorbed)
194
Why are palladium, rhodium and platinum examples of good catalysts?
They have an ideal adsorption strength
195
Why might having palladium, rhodium and platinum as catalysts not be a good idea?
They are expensive
196
What happens to catalysts when their surface area is increased?
It makes them more efficient, decreasing the cost
197
What is used to catalyse the Haber process?
Iron
198
How is the iron catalyst present in the Haber process?
In pea sized lumps to provide a large surface area
199
How can surface area be maximised in the Haber process?
By using a very thin coating of the catalyst on some type of support medium - often honeycomb structure used as a support
200
What is an example of where a honeycomb support structure is used to increase SA?
Rhodium in catalytic converters
201
What does it mean, that some surface catalysts are prone to poisoning?
Other substances adsorb strongly to the surface, blocking the active sites
202
How does poisoning affect a surface catalyst?
Lowers the efficiency of the catalyst or makes it totally ineffective depending on the extent of the poisoning
203
How difficult are poisons to remove from catalysts?
Very difficult
204
What happens when a catalyst is poisoned? Why is this?
They need to be replaced as the poisons are very difficult to remove
205
Examples of catalyst poisoning?
* lead poisoning of catalytic converters in cars
| * sulphur poisoning in the Haber process
206
How can there be catalyst poisoning in catalytic converters?
Both the Rh and Pt catalysts are poisoned by lead from petrol, and these catalysts can be very expensive to replace
207
Why is petrol now unleaded?
To stop the poisoning of the Rh and Pt catalysts from the lead in petrol - however there still tends to be traces of lead present
208
How can there be catalyst poisoning in the Haber process?
The hydrogen for the Haber process is obtained from natural gas which is contaminated by S - trace amounts are found in the product as impurities, which if not removed will poison the Fe catalyst
209
Why is sulphur added to natural gas?
To give it an odour so leaks can be smelt
210
How often does the catalyst need to replaced in the Haber process?
About every 5 years
211
What are homogenous catalysts?
Catalysts which are in the same phase as the reactants, and involve an intermediate
212
What do homogenous catalysts involve?
An intermediate
213
What type of catalyst can have catalyst poisoning?
Heterogenous catalysts
214
What reactions involving homogenous catalysts are required for A level?
* between I- and S2O8²⁻
| * between C2O4²⁻ and MnO4⁻
215
Why is a catalyst required in the reaction of I- and S2O8²⁻?
Both ions are negatively charged and therefore unlikely to make successful collisions
216
How can the ions in the reaction of I- and S2O8²⁻ be made to collide?
With the addition of positive ions
217
What is the reaction rate between I- and S2O8²⁻?
Very slow as -ve ions repel each other so there is a low chance of successful collisions
218
What are the oxidation, reduction and overall equations for the reaction between I- and S2O8²⁻ with an iron catalyst?
oxidation: 2I⁻ → I₂ + 2e⁻ and Fe²⁺ → Fe³⁺ + e⁻
reduction: S2O8²⁻ + 2e⁻ → 2SO4²⁻ and Fe³⁺ + e⁻ → Fe²⁺
overall: S2O8²⁻ + 2Fe²⁺ → 2Fe³⁺ + 2SO4 and 2I⁻ + 2Fe³⁺ → 2Fe²⁺ + I₂
219
What is the catalyst and in the intermediate in the equations S2O8²⁻ + 2Fe²⁺ → 2Fe³⁺ + 2SO4 and 2I⁻ + 2Fe³⁺ → 2Fe²⁺ + I₂?
Catalyst: Fe²⁺
Intermediate: Fe³⁺
220
What is the reaction rate when MnO4- is titrated with a warmed acified solution of C2O4²⁻?
Initially quite slow, and for the first addition of the MnO4⁻ the purple colour is slow to decolourise
221
In the reaction of MnO4- with C2O4²⁻, why, as the reaction continues, does the purple colour immediately turn colourless until the end point is reached?
The Mn2+ produced catalyses the reaction
222
What is autocatalysis?
Where the catalyst of a reaction is one of the products of the reaction
223
Why is the reaction of MnO4- with C2O4²⁻ slow to begin with?
The reactant ions are both negatively charged and are unlikely to collide successfully
224
When will the reaction between MnO4- with C2O4²⁻ speed up?
When the reaction has produced some Mn2+ ions
225
What are the half equations and full equation for the reaction between MnO4- with C2O4²⁻?
oxidation: C2O4²⁻ → 2CO2 + 2e⁻ (x5)
reduction: MnO4⁻ + 8H+ + 5e⁻ → Mn2+ + 4H2O
overall: 2MnO4⁻ + 16H+ + 5C2O4²⁻ → 2Mn2+ + 10CO2 + 8H2O
226
Which complex undergoes incomplete substitution?
[Cu(H2O)6]2+ with NH3
227
What does [Cu(H2O)6]2+ undergo incomplete substitution with?
NH3
228
When would there be complete substitution between [Cu(H2O)6]2+ and NH3?
Concentrated NH3 is required in ice cold conditions
229
How many NH3 are substituted into [Cu(H2O)6]2+?
4
230
When there has been incomplete substitution of NH3 into [Cu(H2O)6]2+, what shape is the complex?
NH3 ligands sit in square planar positions
231
What does the incomplete substitution of [Cu(H2O)6]2+ form?
[Cu(NH3)4(H2O)2]2+
232
What is haem?
An iron(II) complex with a multidentate ligand
233
What type of isomerism is cis-trans?
E-Z
234
What type of catalysts are used in the Haber and contact processes?
Heterogenous
