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AQA A Level Inorganic Chemistry > 5. Transition Metals > Flashcards

5. Transition Metals Flashcards

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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

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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

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3
Q

Why is Cu a transition metal?

A

For Cu 2+ [[Ar] 3d9] it has an incomplete d sub-shell

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4
Q

Physical properties of transition metals?

A
  • conduct heat and electricity
  • malleable and ductile
  • hard and strong
  • dense
  • high melting point
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5
Q

Chemical properties of transition metals?

A
  • can form complexes
  • form coloured compounds
  • have variable oxidation states
  • can act as catalysts
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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

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7
Q

What are bidentate ligands?

A

Ligands that can donate 2 lone pairs of electrons

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8
Q

What are monodentate ligands?

A

Ligands that can donate 1 lone pair of electrons

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9
Q

Examples of monodentate ligands?

A

H2O, NH2, CN- and Cl-

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10
Q

Examples of bidentate ligands?

A
  • NH2CH2CH2NH2

* C₂O₄²⁻

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11
Q

What are multidentate ligands?

A

Ligands that can donate more than two pairs of lone electrons

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12
Q

Example of a multidentate ligand?

A

EDTA⁴⁻

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13
Q

What is a complex?

A

A cenral metal ion surrounded by ligands

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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

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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

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16
Q

What is formed when a transition metal is in an aqueous solution?

A

A hexaaqua ion

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17
Q

What are hydrated complex ions also called?

A

Hexaaqua ions

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18
Q

What is the coordination number?

A

The number of coordinate bonds formed by ligands around the central metal ion

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19
Q

What must the coordination number not be confused with?

A

The number of ligands bonded

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20
Q

What does the coordination number determine?

A

The shape of the complex

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21
Q

What shape is formed if a complex has two coordinate bonds?

A

Linear

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22
Q

What shape is formed if a complex has four coordinate bonds?

A

Tetrahedral or square planar

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23
Q

What shape is formed if a complex has six coordinate bonds?

A

Octahedral

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24
Q

What shape do complexes with Cl- ligands make?

A

Tetrahedral

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25
Q

What is the coordination number of octahedral complexes?

A

6

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26
Q

What are octahedral complexes commonly formed from?

A

Small ligands e.g. H2O and NH3

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27
Q

What type of isomerism can octahedral complexes display? And with what?

A

Cis-trans isomerism with monodentate ligands

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28
Q

Where are the ligands on a cis complex?

A

On the same side

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29
Q

Where are the ligands on a trans complex?

A

On opposite sides

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30
Q

When can octahedral complexes display optical isomerism?

A

When there are two or more bidentate ligands in the complex

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31
Q

When does optical isomerism occur?

A

When the two isomers (enantiomers) exist as two non-superimposable mirror images

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32
Q

What does a ligand substitution involve?

A

Breaking the coordinate bond between the transition metal and the ligand

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33
Q

How can the overall effect of ligand substitution on a molecule be determined?

A

The type of ligand needs to be determined

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34
Q

What types of ligand are there?

A
  • monodentate
  • bidentate
  • multidentate
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35
Q

What is a monodenate ligand?

A

A ligand with one atom capable of donating a lone pair of electrons forming one coordinate bond

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36
Q

Examples of monodenate ligands?

A

H20, NH3 and CL=l-

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37
Q

What shape complex do H2O and NH3 form? Why is this?

A

Octahedral as they are small ligands that can form 6 bonds with the central metal ion

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38
Q

What shape complexes do Cl- form? Why is this?

A

Tetrahedral - repulsion between 6 Cl- is too great and only 4 bonds are formed with the central metal ion

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39
Q

What happens if a neutral ligand is replaced with a neutral ligand?

A

No change in shape, charge, or coordination number

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40
Q

What happens if a neutral ligand is replaced with Cl-?

A

Change in charge, coordination number and shape - octahedral to tetrahedral

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41
Q

What happens if a neutral ligand is replaced with CN-, EDTA4- or C2O4 2-?

A

Change in charge, no change in coordination number or shape

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42
Q

What should be noted about the formation of [Cu(NH3)4(H2O)2]2+ from (Cu(H2O)6)2+?

A

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

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43
Q

What can a change of the H2O ligand by Cl- involve?

A

A change in coordination number and charge on the complex

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44
Q

What is a bidentate ligand?

A

Ligands that have 2 atoms capable of donating an electron pair forming two coordinate bonds

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45
Q

Examples of bidentate ligands?

A
  • 1,2-diaminoethane (NH2CH2CH2NH2)

* ethanedivoate ions (C2O4 2-)

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46
Q

What is a multidentate ligand?

A

A ligand with a number of atoms capable of donating an electron pair producing several coordinate bonds

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47
Q

Examples of multidentate ligands?

A
  • EDTA 4-

* porphyrin (haem)

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48
Q

Example of what complex porphyrin is involved in?

A

Haemoglobin - with an Fe centre

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49
Q

What is haemoglobin?

A

An Fe2+ centre with porphyrin forming 6 coordinate bonds

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50
Q

What is the shape of haemoglobin?

A

Octahedral

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51
Q

How is oxygen transported in the blood?

A

Oxygen binds to haemaglobin

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52
Q

How many O2 molecules are attached to a fully saturated oxyhaemoglobin?

A

4

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53
Q

Why is carbon monoxide toxic?

A

It binds very strongly to haemoglobin; it replaces oxygen co-ordinately bonded to Fe(II)

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54
Q

What is the chelate effect?

A

When bi and multidentate ligands replace monodentate ligands from complexes

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55
Q

What type of ligands are known as chelating ligands?

A

Bi and multi

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56
Q

Why can multi dentate ligands be used to remove d-block metal ions from solution via a substitution reaction?

A

Due to the stability of the complex they form

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57
Q

Through what reaction do multi dentate ligands remove d-block metal ions from solution?

A

Substitution

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58
Q

What happens when mono dentate ligands are replaced with bidentate?

A

Makes complex more stable (chelate effect)

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59
Q

How can a complex be made more stable?

A

If a single ligand makes more bonds with the metal ion the more stable the complex will be

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60
Q

Why is the substitution of bi and multi dentate ligands difficult to reverse?

A

The product of both reactions are more stable than the reactant complex

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61
Q

How can the stability of complexes with chelating ligands be explained?

A

In terms of the increase in entropy of the system

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62
Q

What is the overall feasibility of the reaction involving chelating ligands determined using?

A

ΔG = ΔH - TΔS

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63
Q

In ΔG = ΔH - TΔS, what does G stand for?

A

Gibbs free energy

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64
Q

In ΔG = ΔH - TΔS, what does T stand for?

A

Temperature

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65
Q

In ΔG = ΔH - TΔS, what does S stand for?

A

Entropy

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66
Q

In ΔG = ΔH - TΔS, what does H stand for?

A

Enthalpy

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67
Q

In ΔG = ΔH - TΔS, what value must G take for the reaction to be feasible?

A

Negative

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68
Q

What is entropy?

A

Measure of disorder

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69
Q

In ΔG = ΔH - TΔS, what will the value of ΔH be?

A

Close to 0 as there is a similar type and number of bonds broken and formed

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70
Q

During ligand substitution, what does the entropy value depend on?

A

The number of particles moving freely in solution

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71
Q

Why is feasibility of ligand substitution largely due to change in entropy?

A

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

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72
Q

What does an increase in number of particles mean for entropy?

A

Increase in disorder, therefore entropy

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73
Q

What does an increase in number of particles mean for TΔS?

A

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

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74
Q

Can octahedral complexes display optical isomerism?

A

Yes, when there are two or more bidentate ligands in the complex

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75
Q

When can octahedral complexes display optical isomerism?

A

When there are two or more bidentate ligands in the complex

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76
Q

What is the coordination number of tetrahedral complexes?

A

4

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77
Q

What does it mean that a tetrahedral complex has a coordination number of 4?

A

The central metal ion forms 4 bonds

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78
Q

What are tetrahedral complexes commonly formed from?

A

Larger ligands e.g. Cl

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79
Q

What complexes adopt a square planar shape?

A

Some complexes with a coordination number of 4

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80
Q

What can square planar complexes display?

A

Cis-trans isomerism

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81
Q

Is cisplatin the cis or trans isomer?

A

Cis

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82
Q

What is a cis isomer?

A

When the same groups are on the same side of the central metal ion

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83
Q

What is a trans isomer?

A

When the same groups are on opposite sides of the central metal ion

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84
Q

What is the coordination of linear complexes?

A

2

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85
Q

What does it mean that the coordination number of linear complexes is 2?

A

The central metal ion forms 2 bonds

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86
Q

What are linear complexes commonly formed from?

A

The metal ion Ag+

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87
Q

What shape complex is Tollen’s reagent?

A

Linear

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88
Q

What is the name for [Ag(NH3)2]?

A

Tollen’s reagent

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89
Q

Is silver a transition metal?

A

No

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90
Q

What does the colour of a complex depend on?

A
  • oxidation state of metal centre
  • coordination number
  • ligand
  • the metal itself
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91
Q

Why are transition metals coloured?

A
  • 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
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92
Q

When does colour arise?

A

When some wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected

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93
Q

What energy do the 5 orbitals in the d sub level have? Are there any exceptions to this?

A

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

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94
Q

How can an electron be promoted from ground to excited state?

A

By absorbing certain frequencies of radiation from the visible light spectrum

95
Q

Why, in a complex ion, do the d sub levels move to two different energy levels?

A

Due to the repulsion of ligands

96
Q

How is the energy absorbed between two orbitals summarised?

A

ΔE = hv = hc/ƛ

97
Q

Why might a species not appear to be coloured?

A

If there are no d electrons or if the d orbitals are full

98
Q

What property can be used to identify transition metals?

A

The fact that each will absorb visible radiation of a different frequency and appear a different colour

99
Q

What factors can change the energy of d orbitals and therefore the colour of transition metals?

A
  • oxidation state of metal centre
  • coordination number
  • ligand
100
Q

What colour is the complex [Co(H₂O)₆]²⁺?

A

Pink

101
Q

What colour is the complex [Cu(H₂O)₆)²⁺?

A

Blue

102
Q

What colour is the complex [Fe(H₂O)₆)²⁺?

A

Green

103
Q

What colour is the complex [Fe(H₂O)₆)³⁺? Why might this not be the case?

A

Violet

these solutions may appear different colours due to the presence of other complex ions which exist in equilibrium

104
Q

What colour is the complex [Al(H₂O)₆)³⁺?

A

Colourless

105
Q

Why is the complex [Al(H₂O)₆)³⁺ colourless?

A

It has a complete d sub level so it is not a transition metal, so electrons can’t be excited

106
Q

What does the amount of light absorbed by a transition metal solution depend on?

A

How many ions it interacts with

107
Q

What does the wavelength of radiation absorbed by a transition metal depend on compared to the quantity of the radiation?

A
  • wavelength depends of nature of ion

* quantity of radiation absorbed depends on concentration of coloured solution and distance that light travels

108
Q

What does the quantity of radiation absorbed by a transition metal solution depend on?

A
  • concentration of coloured solution

* distance that light travels

109
Q

What does a spectrophotometer do?

A

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
Q

What is a spectrophotometer also known as?

A

A colorimeter

111
Q

How is the absorbance of radiation measured using a colorimeter?

A
  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
Q

What graph is plotted in UV/visible spectrometry/colorimetry?

A

Calibration graph of concentration against absorbance

113
Q

What is UV/visible spectrometry/colorimetry used for?

A

To find unknown concentration

114
Q

What does the height of the peak on a wavelength-absorption graph depend on?

A

The concentration of the solution, and may be compared to standard charts

115
Q

What is colorimetry?

A

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
Q

What is the oxidation state of an element in a compound?

A

The hypothetical charge an atom in a compound would carry if the compound were 100% ionic

117
Q

What is the oxidation state of a simple ion?

A

Charge on ion

118
Q

What is the oxidation state of group 1 metals in a compound?

A

+1

119
Q

What is the oxidation state of group 2 metals in a compound?

A

+2

120
Q

What is the oxidation state of P block elements?

A

Variable

121
Q

What is the oxidation state of fluorine in a compound?

A

-1

122
Q

What is the oxidation state of chlorine in a compound (except with F and O)?

A

-1

123
Q

What is the oxidation state of hydrogen in a compound (except ionic halides)?

A

+1

124
Q

What is the oxidation state of oxygen in a compound (except peroxides and F2O)?

A

-2

125
Q

What is the sum of oxidation states in a polyatomic ion?

A

Overall charge

126
Q

What is the sum of oxidation states of all the elements in a compound?

A

0

127
Q

Up to Mn ([Ar]3d54s2), what is the maximum oxidation state?

A

The total number of electrons in the 3d and 4s orbitals

128
Q

What charge ions do transition metals form? Are there any exceptions to this?

A

2+ with the exception of Sc → 3+

129
Q

Why is Sc³⁺ especially stable?

A

As it has a noble gas structure

130
Q

When does the 2+ oxidation state of transition metals become more stable?

A

As the atomic number increases

131
Q

Why does an increase in atomic number make the 2+ oxidation state more stable?

A

The increase in nuclear charge makes it more difficult to remove the d electrons

132
Q

What can happen to a transition metal in a redox reaction?

A

Metal ion can be oxidised or reduced

133
Q

How many oxidation states can Vanadium exist in solution?

A

4

134
Q

How are the different oxidation states of Vanadium in solutions identified?

A

By the colour of the solution

135
Q

In VO₂⁺, what is the oxidation state of Vanadium?

A

+5

136
Q

In VO²⁺, what is the oxidation state of Vanadium?

A

+4

137
Q

In V³⁺, what is the oxidation state of Vanadium?

A

+3

138
Q

In V²⁺, what is the oxidation state of Vanadium?

A

+2

139
Q

What is the colour of VO₂⁺?

A

Yellow

140
Q

What is the colour of VO₂⁺?

A

Blue

141
Q

What is the colour of V³⁺?

A

Green

142
Q

What is the colour of V²⁺?

A

Violet

143
Q

How to remember colours of Vanadium in compounds (decreasing oxidation states)?

A

You - yellow

Better - blue

Get - green

Vanadium - violet

144
Q

How can Vanadium (V) be reduced through each oxidation state?

A

By zinc metal in acidic solution

145
Q

What is the overall equation for the complete reduction of Vanadium (V)?

A

2VO₂⁺ + 3Zn + 8H⁺ → 2V²⁺ + 3Zn²⁺ + 4H₂O

146
Q

How is the equation for the complete reduction of Vanadium derived (2VO₂⁺ + 3Zn + 8H⁺ → 2V²⁺ + 3Zn²⁺ + 4H₂O)?

A
  • reduction: VO₂⁺ + 4H⁺ + 3e⁻ → V²⁺ + 2H₂O

* oxidation: Zn → Zn²⁺ + 2e⁻

147
Q

What is the formula for diammine silver (I)?

A

[Ag(NH₃)₂]⁺

148
Q

Which is the active ion in Tollen’s reagent?

A

Diammine silver (I)

149
Q

How is diammine silver reduced to silver?

A

By oxidising aldehydes (but not ketones) to a carboxylate anion (in a carboxylic acid)

150
Q

What does the redox potential of an atom or ion show?

A

How easy it is to be reduced to a lower oxidation state

151
Q

What can redox potentials also be called?

A

Electrode potentials

152
Q

What does it mean if an ion has a more positive value of redox potential?

A

The more likely the ion is to be reduced

153
Q

When can redox potentials for the same reaction change?

A

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
Q

What affects the size of the redox potential?

A

The conditions i.e. H+/OH- ions and pH

155
Q

In what pHs will redox potential be more positive?

A

Acidic as the ion will be more easily reduced

156
Q

What does a redox titration do?

A

Finds out how much oxidising agent is needed to react exactly with a given quantity of reducing agent (and vice versa)

157
Q

Why are transition metals often found in oxidising and reducing agents?

A

They have variable oxidation states

158
Q

Why are transition metals useful to find the end point during a titration?

A

The different colour of their varied oxidation state

159
Q

In the two specific redox titration reactions required for a level, what happens to MnO₄⁻?

A

It is reduced to Mn²⁺ during a titration

160
Q

What reducing agents are used in the reduction of MnO₄⁻?

A

Fe²⁺ and C₂O₄²⁻

161
Q

What are the half equations and therefore overall equation for the reduction of MnO₄⁻ using Fe²⁺?

A

oxidation: 5Fe²⁺ → 5Fe³⁺ + 5e⁻
reduction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
overall: MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O

162
Q

What is the reaction ratio for the reduction of MnO₄⁻ using Fe²⁺?

A

5:1
Fe:MnO₄

163
Q

What are the half equations and therefore overall equation for the reduction of MnO₄⁻ using C₂O₄²⁻?

A

oxidation: 5C₂O₄²⁻ → 10CO₂ + 10e⁻
reduction: 2MnO₄⁻ + 16H⁺ + 10e⁻ → 2Mn²⁺ + 8H₂O
overall: 2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 10CO₂ + 8H₂O

164
Q

What is the reaction ratio for the reduction of MnO₄⁻ using C₂O₄²⁻?

A

5:2

C₂O₄²⁻:MnO₄⁻

165
Q

What is the indicator in the reduction of MnO₄⁻?

A

None - self-indicating

166
Q

What is the colour change at the end point in the reduction of MnO₄⁻?

A

Colourless to light pink

167
Q

Why, in the reduction of MnO₄⁻, is the colour change at the end point colourless to light pink?

A

Due to the presence of the first drop of MnO₄⁻ in excess

168
Q

Why does the MnO₄⁻ appear to be pale pink at one drop of excess in the redox titration?

A

It is largely diluted in solution

169
Q

What is a suitable acid in the redox titration of MnO₄⁻?

A

Dilute H2SO4

170
Q

What are unsuitable acids in the redox titration of MnO₄⁻, and why?

A
  • 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
Q

In redox titrations, what usually goes in the burette?

A

The oxidising agent (i.e. MnO₄⁻ for A level examples)

172
Q

What are catalysts?

A

Substances that speed up the rate of chemical reactions, without being chemically changed, by providing a route to lower Ea

173
Q

Are transition metals used as catalysts?

A

Yes

174
Q

How do catalysts provide a surface for reactions to occur?

A

By forming weak bonds to the reacting species, holding them in place

175
Q

Why can transition metals catalyse certain redox reactions?

A

They can form more than one stable oxidation state and so can accept and lose electrons easily

176
Q

What types of catalysts can transition metals behave as?

A

Heterogenous or homogenous

177
Q

What is the main step in the manufacture of sulphuric acid?

A

The oxidation of sulphur dioxide to sulphur trioxide

178
Q

What is the equation for the oxidation of sulphur dioxide to sulphur trioxide?

A

SO₂ + O₂ → 2SO₃

179
Q

What is the process called in which V2O5 behaves as a catalyst in the manufacture of sulphuric acid?

A

The contact process

180
Q

What reactions show V₂O₅ in the contact process?

A
  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
Q

What is the intermediate of V₂O₅ in the contact process?

A

V₂O₄

182
Q

What are heterogeneous catalysts?

A

Those that are in a different phase to the reactants

183
Q

Why are metals used in heterogeneous catalysis?

A

They are solid and in a different phase to the reactants

184
Q

Where does heterogenous catalysis occur?

A

At the surface of the metal

185
Q

How does a heterogenous catalyst work?

A

By allowing reactant molecules to bond to the surface of the metal, usually by attracting the surface electrons

186
Q

What is the process where at least one of the reactants binds to the surface of the metal?

A

Adsorption

187
Q

What does adsorption do?

A

Weakens bonds within reactant molecules

188
Q

What are active sites?

A

Places on the surface where molecules are adsorbed

189
Q

What can molecules do in an effective catalyst?

A

Move about the surface, bonding to different active sites

190
Q

What happens in heterogenous catalysis when new products are made?

A

The products are desorbed from the surface to make way for new reactant molecules

191
Q

How can the adsorption of reactants onto the surface result in increased reaction?

A
  • 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
Q

What happens if adsorption is too weak?

A

Not many molecules will be adsorbed so the catalyst will have very little effect

193
Q

What happens if adsorption is too strong?

A

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
Q

Why are palladium, rhodium and platinum examples of good catalysts?

A

They have an ideal adsorption strength

195
Q

Why might having palladium, rhodium and platinum as catalysts not be a good idea?

A

They are expensive

196
Q

What happens to catalysts when their surface area is increased?

A

It makes them more efficient, decreasing the cost

197
Q

What is used to catalyse the Haber process?

A

Iron

198
Q

How is the iron catalyst present in the Haber process?

A

In pea sized lumps to provide a large surface area

199
Q

How can surface area be maximised in the Haber process?

A

By using a very thin coating of the catalyst on some type of support medium - often honeycomb structure used as a support

200
Q

What is an example of where a honeycomb support structure is used to increase SA?

A

Rhodium in catalytic converters

201
Q

What does it mean, that some surface catalysts are prone to poisoning?

A

Other substances adsorb strongly to the surface, blocking the active sites

202
Q

How does poisoning affect a surface catalyst?

A

Lowers the efficiency of the catalyst or makes it totally ineffective depending on the extent of the poisoning

203
Q

How difficult are poisons to remove from catalysts?

A

Very difficult

204
Q

What happens when a catalyst is poisoned? Why is this?

A

They need to be replaced as the poisons are very difficult to remove

205
Q

Examples of catalyst poisoning?

A
  • lead poisoning of catalytic converters in cars

* sulphur poisoning in the Haber process

206
Q

How can there be catalyst poisoning in catalytic converters?

A

Both the Rh and Pt catalysts are poisoned by lead from petrol, and these catalysts can be very expensive to replace

207
Q

Why is petrol now unleaded?

A

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
Q

How can there be catalyst poisoning in the Haber process?

A

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
Q

Why is sulphur added to natural gas?

A

To give it an odour so leaks can be smelt

210
Q

How often does the catalyst need to replaced in the Haber process?

A

About every 5 years

211
Q

What are homogenous catalysts?

A

Catalysts which are in the same phase as the reactants, and involve an intermediate

212
Q

What do homogenous catalysts involve?

A

An intermediate

213
Q

What type of catalyst can have catalyst poisoning?

A

Heterogenous catalysts

214
Q

What reactions involving homogenous catalysts are required for A level?

A
  • between I- and S2O8²⁻

* between C2O4²⁻ and MnO4⁻

215
Q

Why is a catalyst required in the reaction of I- and S2O8²⁻?

A

Both ions are negatively charged and therefore unlikely to make successful collisions

216
Q

How can the ions in the reaction of I- and S2O8²⁻ be made to collide?

A

With the addition of positive ions

217
Q

What is the reaction rate between I- and S2O8²⁻?

A

Very slow as -ve ions repel each other so there is a low chance of successful collisions

218
Q

What are the oxidation, reduction and overall equations for the reaction between I- and S2O8²⁻ with an iron catalyst?

A

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
Q

What is the catalyst and in the intermediate in the equations S2O8²⁻ + 2Fe²⁺ → 2Fe³⁺ + 2SO4 and 2I⁻ + 2Fe³⁺ → 2Fe²⁺ + I₂?

A

Catalyst: Fe²⁺

Intermediate: Fe³⁺

220
Q

What is the reaction rate when MnO4- is titrated with a warmed acified solution of C2O4²⁻?

A

Initially quite slow, and for the first addition of the MnO4⁻ the purple colour is slow to decolourise

221
Q

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?

A

The Mn2+ produced catalyses the reaction

222
Q

What is autocatalysis?

A

Where the catalyst of a reaction is one of the products of the reaction

223
Q

Why is the reaction of MnO4- with C2O4²⁻ slow to begin with?

A

The reactant ions are both negatively charged and are unlikely to collide successfully

224
Q

When will the reaction between MnO4- with C2O4²⁻ speed up?

A

When the reaction has produced some Mn2+ ions

225
Q

What are the half equations and full equation for the reaction between MnO4- with C2O4²⁻?

A

oxidation: C2O4²⁻ → 2CO2 + 2e⁻ (x5)
reduction: MnO4⁻ + 8H+ + 5e⁻ → Mn2+ + 4H2O
overall: 2MnO4⁻ + 16H+ + 5C2O4²⁻ → 2Mn2+ + 10CO2 + 8H2O

226
Q

Which complex undergoes incomplete substitution?

A

[Cu(H2O)6]2+ with NH3

227
Q

What does [Cu(H2O)6]2+ undergo incomplete substitution with?

A

NH3

228
Q

When would there be complete substitution between [Cu(H2O)6]2+ and NH3?

A

Concentrated NH3 is required in ice cold conditions

229
Q

How many NH3 are substituted into [Cu(H2O)6]2+?

A

4

230
Q

When there has been incomplete substitution of NH3 into [Cu(H2O)6]2+, what shape is the complex?

A

NH3 ligands sit in square planar positions

231
Q

What does the incomplete substitution of [Cu(H2O)6]2+ form?

A

[Cu(NH3)4(H2O)2]2+

232
Q

What is haem?

A

An iron(II) complex with a multidentate ligand

233
Q

What type of isomerism is cis-trans?

A

E-Z

234
Q

What type of catalysts are used in the Haber and contact processes?

A

Heterogenous

AQA A Level Inorganic Chemistry (6 decks)

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