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3.2.5 - Transition Metals Flashcards

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1
Q

What is a transition metal?

A

A metal which can form at least one stable ion with a partially filled d sub-level.

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2
Q

Are Sc and Zn transition metals? Explain why / why not.

A

NOT TRANSITION METALS.

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3
Q

What are the 4 characteristic properties of transition metals?

A
  1. Form complex ions
  2. Form coloured ions
  3. Have variable oxidation states
  4. Can act as catalysts.
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4
Q

What is a complex?

A

A central metal atom / ion surrounded by ligands.

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5
Q

What is a ligand?

A

A species which can use its lone pair to form a dative covalent bond to a transition metal.

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6
Q

What is meant by co-ordination number?

A

Number of co-ordinate bonds to the central metal atom/ion.

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7
Q

What can act as a poison in the Haber process?

A

Sulphur.

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8
Q

What can act as a poison in a catalytic converter?

A

Lead.

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9
Q

What property of transition metals allows them to be catalysts?

A

Variable oxidation states.

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10
Q

Where are transition metals?

A

D-Block Elements.

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11
Q

What are the 2 elements that are not transition metals?

A

Zinc and Scandium.

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12
Q

Define Transition metal:

A

A d-Block element that can form at least one stable ion with a partially filled d-subshell.

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13
Q

How many T.M?

A

8.

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14
Q

How do electrons fill up shells?

A

Fill up singly at first, and then double-up.

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15
Q

Explain the Obsolete nature of Chromium?

A

One electron jumps from the 4s to the 3d because the 3d is half full and much more stable than the 4s.

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16
Q

How does Iron lose its electrons?

A

4s first and then 3d.

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17
Q

Properties of transition metals:

A
  1. Specific properties such as variable oxidation states.
  2. Electrons are gained and lost using a similar amount of energy.
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18
Q

Explain the colour change from a Vanadium molecule to a v2+ Ion.

A

Forms violet colour.

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19
Q

Explain the colour change from Vanadium to V3+ Ion.

A

Forms green solution.

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20
Q

Explain the colour change from Vanadium to VO2+ Ion.

A

Blue colour.

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21
Q

Explain the colour change from Vanadium to VO(2+) Ion.

A

YELLOW LIQUID.

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22
Q

Explain the colour change from Chromium to Cr3+ Ion.

A

Green / violet. Violet when surrounded by 6H2O.

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23
Q

Explain the colour change from Chromium to Cr2 O7 (2-) Ion.

A

Orange.

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24
Q

Explain the colour change from Manganate to Mn 2+ Ion.

A

Pink colour.

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25
Q

Explain the colour change from Manganate to Mn O4- Ion.

A

Purple colour.

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26
Q

Define Ligand:

A

An atom which has at least one lone pair of electrons.

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27
Q

Explain the Monodentate ligand:

A
  1. Monoligand - Only one lone pair of electrons.
  2. Examples: H2O, NH3, Cl-.
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28
Q

Explain Bidentate ligand:

A
  1. A ligand which has 2 lone pairs.
  2. Examples: ethanedioate, ethane-1,2-diamine.
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29
Q

Explain Multidentate ligand:

A
  1. Ligand which has more than 1 co-ordinate bonds.
  2. Examples: HAEM, EDTA 4-.
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30
Q

Define co-ordination number.

A

The number of co-ordinate bonds in a complex.

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31
Q

Give an example of a small ligand.

A

H2O, NH3.

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32
Q

Give an example of a medium ligand.

A

Cl-.

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33
Q

Give an example of a large ligand.

A
  1. Ethanedioate.
  2. Ethane-1,2-diamine.
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34
Q

Explain what a metal complex ion is:

A

Central transition metal ion surrounded by ligand and a bonded dative covalent bond.

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35
Q

Complex ion with a co-ordinate number of 6.

A

Octahedral shape with 90 degrees bond angle.

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36
Q

Complex ion with a co-ordinate number of 4.

A

Example is Cis-Platin - 90 degree bond angle.

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37
Q

Complex ion with a co-ordinate number of 2 form a linear shape.

A

Examples: Silver complexes, Tollens Reagent.

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38
Q

How do you calculate the total oxidation of a complex ion?

A

Refer to the provided equations.

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39
Q

Draw the structure of Haemoglobin.

A

Refer to the provided image.

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40
Q

Where do the ligands come from in a Hb molecule?

A

4 of the ligands come from one multidentate called Haem, one from Globin, and one from either a water or an oxygen molecule.

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41
Q

How does Hb transport oxygen?

A

O2 substitutes the water ligand in the lungs to form oxyhaemoglobin, which is transported around the body.

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42
Q

Symptoms of carbon monoxide poisoning?

A
  1. Headaches.
  2. Unconsciousness.
  3. Death.
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43
Q

How does carbon monoxide poisoning occur?

A
  1. Carbon monoxide is inhaled into the lungs.
  2. The carbon monoxide ligand replaces the water ligand.
  3. Body is starved of oxygen.
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44
Q

What are Optical Isomerism?

A

2 molecules which contain an asymmetric carbon atom and mirror images that cannot be superimposed.

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45
Q

Conditions to show optical isomerism:

A
  1. Octahedral.
  2. 3 Bidentate.
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46
Q

Explain how square planar molecules show Cis-Trans isomerism.

A

Example: Cis-Trans platin.

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47
Q

What is a must have for ligands?

A

An atom that has at least one lone pair.

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48
Q

What are the 3 types of ligands?

A
  1. Monodentate.
  2. Bidentate.
  3. Polydentate.
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49
Q

What is monodentate?

A

A ligand with only one lone pair of electrons to donate to a metal ion.

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50
Q

What is a Bi-Dentate ligand?

A

A ligand with 2 lone pairs of electrons to donate to a metal ion.

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51
Q

Polydentate (Multidentate) ligand:

A

A ligand with more than 2 lone pairs of electrons to donate to a metal ion.

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52
Q

What is EDTA an example of?

A

EDTA is an example of a multi-dentate ligand; which can form 6 dative covalent bonds with the central metal ion.

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53
Q

Draw A Haemoglobin ligand.

A

Refer to the provided image.

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54
Q

Explain the process of using a colorimeter?

A
  1. Colorimeter must be at 0 - measure the absorbance of a blank sample.
  2. White light is filtered through a narrow range of frequencies.
  3. Place the sample in a cuvette.
  4. The light that is not absorbed travels to the detector.
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55
Q

What are the physical properties of transition metals?

A
  1. All have a high density.
  2. All have high mp and bp points.
  3. Ionic radii are more or less the same.
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56
Q

Define Complex?

A

Central metal ion surrounded by a coordinately bonded ligand.

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57
Q

How is the standard electrode potential measured in ligands?

A

Measured in aqueous solution; where the metal ion is surrounded by water.

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58
Q

How do ligands influence the redox potential?

A

The stronger the ligand binds to the metal ion; the larger the redox potential.

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59
Q

What are the factors that affect the electrode potentials?

A
  1. Ligand size.
  2. pH.
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60
Q

How do homogeneous catalysts work?

A

Work by reacting with the reactants to form an intermediate compound that reacts to form the products.

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61
Q

Why are transition metals good catalysts?

A

Have variable oxidation states and can easily gain or lose an electron.

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62
Q

What does catalytic positioning do to the catalyst?

A

Binds to its surface, and blocks the active site, reducing the surface area.

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63
Q

Explain ways of reducing percentage uncertainty:

A
  1. Repeating an experiment reduces uncertainty.
  2. Increase the concentration.
  3. Increase the mass.
  4. Use a larger titre.
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64
Q

What is the advantage of a burette?

A

Can deliver variable volumes.

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65
Q

Why is potassium Permanganate (KMNO4) used as an oxidising agent?

A
  1. High reduction potential.
  2. Acts as its own indicator.
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66
Q

Define a complex:

A

A centre metal atom or ion surrounded by co-ordinately bonded ligands.

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67
Q

Show the equation for iron in the Haber process for making ammonia:

A

Refer to the provided equation.

68
Q

Autocatalysis equation

A

Refer to the provided equation.

69
Q

Explain Vanadium as a heterogeneous catalyst:

A

Refer to the provided image.

70
Q

Autocatalysis overall equation:

A

Refer to the provided equation.

71
Q

Define ligand:

A

Particle that forms a co-ordinate bond to a metal ion.

72
Q

Define ligand

A

A particle that forms a co-ordinate bond to a metal ion.

73
Q

Define the term multidentate ligand

A

A ligand that forms three or more co-ordinate bonds to the central metal ion.

74
Q

Draw benzene-1,2-diol; how many co-ordinate bonds can it form to a transition metal ion?

A
75
Q

How many co-ordinate bonds does EDTA4- form?

A

6

76
Q

Why is CO toxic?

A

CO also coordinately bonds to the Fe2+, and is a better ligand, so bonds more strongly than O2. Stops O2 from bonding to haemoglobin, so O2 cannot be transported around the body.

77
Q

What colour is Fe3+’s aqua ion?

A

Pale brown

78
Q

What colour is Cr3+’s aqua ion?

A

Red/violet

79
Q

What colour is Co2+’s aqua ion?

A

Brown

80
Q

What colour is Co3+’s aqua ion?

A

Yellow

81
Q

What colour is MnO4 (-)?

A

Deep Purple

82
Q

What colour is Cr3+?

A

Green

83
Q

Write a half equation for the reduction of Cr2 O7 ^2- to Cr ^3+

A
84
Q

State what happens to aqua metal ions in acidic conditions?

A

Reduced

85
Q

What happens to Metal Aqua ions in Alkaline conditions?

A

They get oxidised.

86
Q

Draw Cis-Platin

A
87
Q

What entropy is the Chelate effect and why?

A

Explained as a positive entropy, as there are more products than reactants.

88
Q

Explain the effect on entropy when ligand substitution from a unidentate ligand to a bidentate ligand?

A

Entropy change when increasing ligand size is positive (entropically favourable) because there are more moles of products than reactants; therefore creating more disorder. Free energy change ΔG° will be negative; as ΔS° is positive and ΔH° is small.

89
Q

What is EDTA used for?

A

EDTA is added to rivers to remove poisonous heavy metal ions as it is nontoxic. It is also used in shampoos to remove calcium ions present within hard water, helping lathering.

90
Q

Draw the Cis-Trans isomerism of Ni(NH3)2Cl2

A
91
Q

What does colour change arise from changes in?

A
  1. Oxidation State 2. Co-ordination Number 3. Ligand.
92
Q

How does colour arise?

A

A portion of visible light is absorbed, exciting electrons from ground state to excited state. The light that is not absorbed is transmitted or reflected to give the substance colour.

93
Q

Equations of ΔE

A
94
Q

What happens if a solution absorbs orange light?

A

It will appear blue.

95
Q

How does changing ligands or coordination number affect the colour?

A

Changing the ligands and changing the coordination number alters the energy split (ΔE) between the d-Orbitals, causing a change in the frequency of light absorbed.

96
Q

Why doesn’t Scandium produce any colour?

A

Sc3+ hasn’t got any d-block electrons left to move around, resulting in no energy transfer equal to light.

97
Q

What do Spectrometers contain?

A

Coloured filter; where the coloured filter is chosen to allow the wavelengths of light through that would most strongly be absorbed by the coloured solution. The amount of light absorbed is proportional to the absorbing species. Some complexes have pale colours and do not absorb light strongly; where a suitable ligand is added to intensify colour.

98
Q

Explain the method of Spectrophotometry:

A
  1. Add appropriate ligand to intensify colour 2. Make up solutions of known concentrations 3. Measure absorption vs transmission 4. Plot graph of absorption vs concentration 5. Measure absorption of unknown and compare.
99
Q

What do compounds with high oxidation states usually do?

A

Usually oxidising agents.

100
Q

What do compounds with low oxidation states usually do?

A

Often reducing agents.

101
Q

Explain vanadium’s 4 main oxidation states:

A
102
Q

What will be the end point, when manganate is in the test tube?

A

The end point will be the first permanent pink colour.

103
Q

What do you use for manganate titrations?

A

Only Dilute Sulfuric Acid (H2SO4).

104
Q

Why can you not use ethanoic acid (weak acid) in a manganate titration?

A

Volume will not be acidic enough where MnO2 will be produced instead of MnO4-. Where the large volume of hydrogen ions (8H+) cannot be supplied from a weak acid.

105
Q

What can concentrated HCl not be used for manganate titrations?

A

Cl- would be oxidised to Cl2 by MnO4-, leading to a greater volume of manganate being used and poisonous Cl2 being produced.

106
Q

What can Nitric Acid (HNO₃) not be used for manganate titrations?

A

Nitric Acid is an Oxidising Agent, where it oxidises Fe2+ to Fe3+.

107
Q

How is the reaction between MnO4- and C2O4 (2-) sped up?

A

Heated to 60 degrees Celsius.

108
Q

What are heterogeneous catalysts usually?

A

Solids, whereas the reactants are gaseous or in solution. Reaction occurs at the surface of the catalyst.

109
Q

What may lead to catalytic action?

A

Adsorption of reactants at active sites on the surface.

110
Q

Where do reactants adsorb?

A

The active site.

111
Q

What have the right adsorption?

A

Ni and Pt have the right adsorption and are the most useful as catalysts.

112
Q

Explain the use of surface area in catalytic activity?

A

Increasing surface area improves effectiveness. Support medium used to maximise the surface area and minimise the cost, e.g. Rh on ceramic support in catalytic converters.

113
Q

Steps in a heterogeneous catalyst?

A
  1. Reactants form bonds with atoms at active sites on the surface of the catalyst (adsorbs) 2. As a result, bonds in the reactant are weakened and break 3. New bonds form between the reactants, held close together on the catalyst surface 4. This weakens the bonds between the product and catalyst and the product desorbs (leaves).
114
Q

What is a must for homogeneous catalysts and their electrode potentials?

A

For a substance to act as a homogenous catalyst; its electrode potential must lie in between the electrode potential of the 2 reactants. Reduces the reactant that is more positive and oxidises the reactant that is least positive.

115
Q

Equation used in MnO4 - Titrations:

A
116
Q

Titration equation with Fe and MnO4-

A
117
Q

Equations of C2O4 2- and MnO4-

A
118
Q

Suggest why the enthalpy change for the reaction is approximately zero?

A

Similar enthalpies. Same number of bonds broken and made.

119
Q

Explain how a co-ordinate bond is formed between a transition metal ion and a ligand:

A

Electron pair on ligand donated from ligand to central metal ion.

120
Q

Fe2+ catalysing reaction:

A

Oppositely charged ions, therefore low activation energy.

121
Q

Explain why Fe3+ are as effective as Fe2+ ions in catalysing this reaction:

A

Equations 1 and 2 can occur in any order.

122
Q

Explain why Fe3+ ions have a lower pH than Fe2+ ions:

A

Fe3+ is a smaller ion with a higher charged density. Fe3+ ions are more polarising, so more O-H bonds break and more H+ ions released.

123
Q

Explain why a Indicator is suitable?

A

Has a colour change.

124
Q

2 bidentate ligands:

A
  1. Ethanedioate 2. C2O4 2-.
125
Q

Why are chloride ions not considered ligands in [Cu(H2O)6]Cl2?

A

Cl- are not forming a coordinate bond with Cu2+.

126
Q

What defines a transition metal and list some general properties?

A

Transition metals are defined by their incomplete d sub-levels in atoms or ions. General properties include complex formation, variable oxidation states, formation of colored ions, and catalytic activity.

127
Q

Provide the electronic configuration for Fe and Cu.

A

Fe: [Ar]4s23d6
Cu: [Ar]4s13d10

128
Q

Explain why zinc is not considered a transition metal.

A

Zinc is not considered a transition metal because its Zn2+ ion has a completely filled d orbital (3d10), not meeting the criterion of having an incomplete d sub-level in one of its common oxidation states.

129
Q

Define a complex and explain the role of ligands in complex formation.

A

A complex is a structure where a central metal ion is surrounded by ligands, which are atoms, ions, or molecules capable of donating a lone pair of electrons. Complex formation involves coordinate bonding where the shared electron pair comes only from the ligand.

130
Q

Explain how the coordination number might change during a ligand substitution reaction involving chloride ions.

A

In the presence of a high concentration of chloride ions, a ligand substitution may lead to a change in coordination number, such as reducing from 6 to 4. For example, [Cu(H2O)6]2+ can react with chloride ions to form the tetrahedral [CuCl4]2−.

131
Q

What role does haem play in biology, and why is it considered a multidentate ligand?

A

Haem is an iron(II) complex with a multidentate organic ring (porphyrin) that binds oxygen. It’s considered multidentate because it can form several coordinate bonds through its nitrogen atoms, essential for oxygen transport in blood.

132
Q

Discuss the use of EDTA in complexing metal ions and its environmental applications.

A

EDTA is a multidentate ligand that forms stable complexes with metal ions. It’s used environmentally to remove toxic heavy metal ions from water bodies as its complexes are non-toxic, and it’s used in shampoos to counteract hard water.

133
Q

What is haem?

A

Haem is an iron(II) complex with a multidentate organic ring (porphyrin) that binds oxygen.

134
Q

Why is haem considered multidentate?

A

Haem is considered multidentate because it can form several coordinate bonds through its nitrogen atoms, essential for oxygen transport in blood.

135
Q

What is EDTA and its environmental application?

A

EDTA is a multidentate ligand that forms stable complexes with metal ions, used to remove toxic heavy metal ions from water bodies.

136
Q

How does EDTA function in shampoos?

A

EDTA is used in shampoos to counteract hard water.

137
Q

What is the chelate effect?

A

The chelate effect refers to the increased stability of complexes involving multidentate ligands due to ring formation.

138
Q

How does the chelate effect impact entropy?

A

The chelate effect often results from an increase in entropy, as more particles are produced in the reaction, leading to greater disorder.

139
Q

What factors influence the color of transition metal complexes?

A

The color can change due to alterations in oxidation state, coordination number, or ligands, affecting the energy splitting (ΔE) in the d orbitals.

140
Q

Why are variable oxidation states significant in transition metals?

A

Variable oxidation states allow transition metals to participate in a wide range of chemical reactions, including redox reactions.

141
Q

Why are transition metal complexes often colored?

A

Transition metal complexes are colored due to d-d electron transitions, where certain wavelengths of light are absorbed to promote electrons between split d orbitals.

142
Q

How does changing a ligand in a transition metal complex affect its color?

A

Changing a ligand alters the split in the d orbitals’ energy levels (ΔE), affecting which wavelengths of light are absorbed.

143
Q

What role does spectrophotometry play in analyzing transition metal complexes?

A

Spectrophotometry measures the intensity of light absorbed at specific wavelengths to determine the concentration of colored transition metal complexes.

144
Q

What is homogeneous catalysis?

A

Homogeneous catalysis involves catalysts and reactants in the same phase, often leading to intermediate complexes.

145
Q

What is heterogeneous catalysis?

A

Heterogeneous catalysis involves catalysts in a different phase from the reactants, typically occurring on the catalyst surface.

146
Q

What are the typical steps in heterogeneous catalysis involving transition metals?

A

1) Adsorption of reactants on the catalyst’s surface, 2) Reaction at active sites, 3) Formation of new bonds and products, 4) Desorption of products.

147
Q

What is catalyst poisoning?

A

Catalyst poisoning occurs when impurities bind to the catalyst’s active sites, blocking the actual reactants from adsorbing and reacting.

148
Q

What are the implications of catalyst poisoning in industrial processes?

A

Catalyst poisoning decreases the efficiency of the catalyst, leading to increased operational costs and the need for more frequent catalyst replacement.

149
Q

What is the role of V2O5 in the Contact Process?

A

V2O5 acts as a catalyst in the Contact Process, facilitating the oxidation of SO2 to SO3.

150
Q

What are the properties and roles of silver complexes?

A

Silver forms linear complexes, such as [Ag(NH3)2]+, used in Tollens’ reagent to distinguish aldehydes from ketones.

151
Q

Why does silver not show variable oxidation states?

A

Unlike typical transition metals, silver does not show variable oxidation states or colored compounds due to its full d subshell.

152
Q

How is EDTA used in analytical chemistry?

A

EDTA is used in titrations to form stable complexes with metal ions, allowing for precise quantification of metal concentrations.

153
Q

What are the chemical properties of transition metals?

A

1) Form complex ions, 2) Form coloured ions, 3) Are good catalysts, 4) Can exist in variable oxidation states.

154
Q

What is a coordinate bond?

A

A coordinate bond is a covalent bond in which both electrons in the shared pair come from the same atom.

155
Q

What is a Lewis base?

A

A Lewis base is a lone pair donor.

156
Q

What is a Lewis acid?

A

A Lewis acid is a lone pair acceptor.

157
Q

How to identify metal ions with test tube reactions?

A

1) Measure out samples of unknown metal ion into 3 test tubes. 2) Add NaOH sol dropwise to 1st and record changes. 3) Add NH3 sol dropwise to 2nd, record changes. 4) Add Na2CO3 dropwise to 3rd, record observations.

158
Q

What is the role of iron as a heterogeneous catalyst in the Haber process?

A

Iron provides a surface for nitrogen and hydrogen to adsorb, facilitating their reaction to form ammonia.

159
Q

How do Fe2+ ions catalyze the reaction between peroxodisulfate (VI) ions and iodide ions?

A

Fe2+ ions undergo redox reactions, being oxidized by S2O8^2− to Fe3+, which then reduces back to Fe2+ by I−, forming I2.

160
Q

Why do Zn2+ ions not catalyze the reaction between peroxodisulfate (VI) ions and iodide ions?

A

Zn2+ ions have only one stable oxidation state (+2) and cannot participate in the necessary redox reactions.

161
Q

Why does [Fe(H2O)6]3+ have a lower pH compared to [Fe(H2O)6]2+?

A

[Fe(H2O)6]3+ ions are more acidic due to higher charge density, leading to increased hydrolysis and more H+ ions being released.

162
Q

What is ligand substitution using an example from iron complexes?

A

In ligand substitution, ligands in a metal complex are replaced by other ligands. For example, [Fe(H2O)6]3+ can react with chloride ions to form [FeCl4]−.

163
Q

How to calculate the energy absorbed by an electron during light absorption?

A

The energy (E) absorbed can be calculated using E = hc/λ, where h is Planck’s constant, c is the speed of light, and λ is the wavelength.

164
Q

How is EDTA used in the colorimetric analysis of metal ions?

A

EDTA forms stable complexes with metal ions, changing the solution’s color, which is measured using a colorimeter.

165
Q

What are the oxidation state and coordination number of cobalt in [Co(NH3)5Cl]Cl2?

A

In [Co(NH3)5Cl]Cl2, cobalt has an oxidation state of +3 and a coordination number of 6.

166
Q

How is colorimetry used to determine the concentration of iron in a solution?

A

A solution containing iron forms a colored complex which absorbs light at a specific wavelength, and the absorbance is compared to a standard calibration curve.

167
Q

How do thermodynamic principles apply to the reactions of transition metals?

A

Reactions often consider enthalpy changes for exothermic or endothermic reactions and entropy changes related to disorder or order in the system.

Chemistry (18 decks)

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