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A Level - Chemistry > 15: Transition Metals > Flashcards

15: Transition Metals Flashcards

1
Q

What are d-block elements?

A

Element in the d-block

Found in the middle of the periodic table

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2
Q

What is a transition metal?

A

D-block elements that can form one or more stable ions with incompletely filled d-orbitals

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3
Q

What is in the d-subshell?

A

5 orbitals that hold 10 electrons

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4
Q

Which period 4 d-block elements are transition metals?

A

All but scandium and zinc

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5
Q

What are the notable differences in the normal electron configuration in period 4?

A

Copper and chromium

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6
Q

How do electrons fill and leave the period 4 d-block elements?

A

Fills and leaves 4s before 3d

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7
Q

What is the electron configuration of Chromium?

A

[Ar] 3d5 4s1

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8
Q

What is the electron configuration of Copper?

A

[Ar] 3d10 4s1

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9
Q

What is [Ar]?

A

The electron config of Argon

1s2 2s2 2p6 3s2 3p6

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10
Q

What is the electron confid of Ti, Ti2+ and Ti3+ ?
Proton number = 22

A

Ti: [Ar] 3d2 4s2

Ti2+: [Ar] 3d2

Ti3+: [Ar] 3d1

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11
Q

Why is scandium not a transition metal?

A

Only forms Sc3+ which has an empty d subshell

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12
Q

What is the electron config of Sc and Sc3+?

A

Sc: [Ar] 3d1 4s2

Sc3: [Ar]

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13
Q

Why is zinc not a transition metal?

A

Only forms Zn2+ which has a full d subshell

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14
Q

What is the electron config of Zn and Zn2+?

A

Zn: [Ar] 3d10 4s2

Zn2+: [Ar] 3d10

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15
Q

How many oxidation states do transition metals typically have?

A

Multiple

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16
Q

What is requireed to form a compound or complex with an ion?

A

Energy out when it forms must be greater than energy to remove outer electrons to form the ion (ionisation energy)

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17
Q

Why can transition metals form ions with different oxidation numbers?

A

4s and 3d are at similar energy levels

Not large increase in ionisation energy to remove successive electrons
Therefore multiple can be removed

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18
Q

How does ionic charge affect energy released when ions form a complex or compound?

A

Greater the ionic charge the more energy is released when a compound or complex forms

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19
Q

What are the energy factor to take into consideration with larger ionic charge?

A

Greater energy given out when compound and complex forms

More energy to remove outer electrons, energy released counteracts this

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20
Q

What is a complex?

A

Complex ion is a metal ion surrounded by dative covaltently coordinately bonded ligands

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21
Q

What is a dative covalent bond?

A

Covalent bond in which both electrons in the shared pair come from the same atom

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22
Q

What is a ligand?

A

Atom, ion or molecule that donates a pair of electrons to a central metal atom or ion

Has at least one lone pair of electrons

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23
Q

Why does a ligand require a lone pair of electrons?

A

Required for the formation of a dative covalent bond

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24
Q

What is a monodentate ligand?

A

Ligands which only form one bond to the central metal ion

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25
Q

What is a bidentate ligand?

A

Ligands that can each form 2 dative covalent bonds with the central metal ion

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26
Q

What is a multi or polydentate ligand?

A

More than two lone pairs over a molecule that can be used to form dative covalent bonds to the metal ion

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27
Q

What is the overall charge on the complex ion?

A

Oxidation number of complex

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28
Q

How are the oxidation numbers in a complex calculated?

A

Oxidation number of metal ion = total oxidation number - sum of charges of ligands

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29
Q

What is the coordination number?

A

Number of dative covalent bonds formed with the central metal ion in the complex

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30
Q

What are the normal coordination numbers?

A

4 or 6

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31
Q

When is the coordination number 6?

A

Ligands are small

H2O, OH-, NH3

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32
Q

When is the coordination number 4?

A

Larger ligands

Cl-

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33
Q

Why are the ligands as far away from eachother as possible in a complex?

A

Electrons in dative covalent bonds repel eachother as much as possible

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34
Q

What is the shape seen in a complex with coordination number 6?

A

Octahedral - 6 bonding pairs

90º bond angle

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35
Q

What is the shape of a complex with a coordination number of 4?

A

Tetrahedral - 109.5º

OR
Square planar - 90º

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36
Q

Which ligands show cis/trans isomerism?

A

Octahedral and square planar

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37
Q

What is the cis isomer of a ligand?

A

Same groups are on the same side

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38
Q

What is the trans isomer of a ligand?

A

Same groups are oppoisite eachother

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39
Q

What is cis-platin?

A

Anti-cancer drug

Square planar - two chloride and two ammonia groups

Chloride are on same side, if trans then would not affect cancer cells

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40
Q

What occurs to the 3d subshell when ligands bond to metal ions?

A

3d orbitals split into two different energy levels

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41
Q

How does the 3d subshell split?

A

3 orbitals remain at ground state

2 promoted to higher energy level

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42
Q

How much does the 3d subshell split?

A

Varies depending on the elements involved

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43
Q

What occurs to electrons in the ground state of the split 3d subshell?

A

Electron absorbs energy of specific frequency to be promoted

Frequency is in visible light

All other frequencies reflected giving colour

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44
Q

How does the frequency of light required to promote change when the excited orbitals have a larger energy gap?

A

Frequency increases to provide extra energy

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45
Q

What does the energy gap between the split 3d subshell depend on?

A

Metal ion present

Oxidation number

Ligands

Coordination number

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46
Q

What occurs to give a coloured complex its colour?

A

Absorbs light of certain frequency for promoting electron

All other frequencies are reflected

Reflected is the colour observed

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47
Q

What is the concept of complementary colours for ligands?

A

Absorb a certain colour

Complementary colour is the opposite in colour wheel, this is what is seen when all not absored is reflected

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48
Q

What colour does [Cu(H2O)6]2+ turn if it absorbs red light?

A

Blue solution

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49
Q

What is the colour of compounds with full or empty 3d orbitals?

A

White or colourless

No energy is absorbed

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50
Q

What occurs when a transition metal ion is dissolved in water?

A

Transition metal ion forms aqueous complex in solution

Ion surrounded by water ligands

Coloured are easily identifiable

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51
Q

What is the colour of the aqueous complex of V5+ (VO2+)?

A

Yellow

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52
Q

What is the colour of the aqueous complex of V4+ (VO2+)?

A

Blue

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53
Q

What is the colour of the aqueous complex of V3+?

A

Green

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54
Q

What is the colour of the aqueous complex of V2+?

A

Violet

55
Q

What is the colour of the aqueous complex of Cr+6 in Cr2O72-?

A

Orange

56
Q

What is the colour of the aqueous complex of Cr3+?

A

Green

57
Q

What is the colour of the aqueous complex of Fe3+?

A

Yellow

58
Q

What is the colour of the aqueous complex of Fe2+?

A

Pale green

59
Q

What is the colour of the aqueous complex of Co2+?

A

Pink

60
Q

What is the colour of the aqueous complex of Cu2+?

A

Pale blue

61
Q

Which oxidation states can vanadium exist as in solution?

A

+2

+3

+4

+5

62
Q

What is the equation of the vanadium ion when its oxidation state is +5?

A

VO2+

63
Q

What is the equation of the vanadium ion when its oxidation state is +4?

A

VO2+

64
Q

What is the ionic half-equation between the +5 and +4 oxidation states of Vanadium?

A

VO2+ + 2H+ + e- ⇔ VO2+ + H2O

65
Q

What is the ionic half-equation between the +4 and +3 oxidation states of Vanadium?

A

VO2+ + 2H+ + e- ⇔ V3+ + H2O

66
Q

What are they probably going to ask about with vanadium?

A 
Reduction potentials (E)
Whether redox reactions occur
67
Q

What are the common oxidation states of chromium?

A

+2

+3

+6

68
Q

What is the colour of the aqueous complex of Cr+6 in CrO4-?

A

Yellow

69
Q

What are the +6 Chromium ions said to be?

A

Good oxidising agents

Easily reduced to Cr3+

70
Q

What is the colour of the aqueous complex of Cr2+?

A

Blue

71
Q

What can be used to reduce dichromate (VI) ions?

A

Zinc and dilute acid

Reduces Cr3+ to Cr2+

72
Q

Why does Cr2+ have to be made in an inert environment?

A

Unstable in air

Unstable as it oxidises straight back to Cr3+ in air

73
Q

How are Cr3+ ions oxidised to dichromate (VI) ions?

A

Hydrogen peroxide in an alkaline solution

74
Q

What does amphoteric mean?

A

Compound or species which can react as both a base and an acid

75
Q

What is a feature of chromium (III) hydroxide?

A

Amphoteric

76
Q

What happens when you react aqueous chromium 3+ with sodium hydroxide?

A

[Cr(H2O)6]3+ + 3OH- → [Cr(OH)3(H2O)3] + 3H2O

Green solution → grey-green precipitate

77
Q

Which is the charge of complexes which are precipitates?

A

Neutral

78
Q

What occurs when you react aqueous chromium 3+ with ammonia?

A

[Cr(H2O)6]3+ + 3NH3 → [Cr(OH)3(H2O)3] + 3NH4+

green solution → grey-green precipitate

79
Q

What occurs when you react chromium hydroxide precipitate with excess sodium hydroxide?

A

[Cr(OH)3(H2O)3] + 3OH- → [Cr(OH)6]3- + 3H2O

Grey-green precipitate → dark green solution

80
Q

What kind of reaction is it when non-excess of NaOH or NH3?

A

H2O ligands are deprotonated to OH-

81
Q

What occurs to chromium hydroxide precipitate when acid is added?

A

[Cr(OH)3(H2O)3] + 3H+ → [Cr(H2O)6]3+

grey-green precipitate → green solution

Protonation

82
Q

What are the reactions between aqueous chromium 3+ complex and sodium hydroxide or ammonia?

A

Acid-base reactions

Not ligand exchange

83
Q

What occurs when excess ammonia is added to the chromium hydroxide precipitate?

A

[Cr(OH)3(H2O)3] + 6NH3 → [Cr(NH3)6]3+ + 3OH- + 3H2O

Ligand exchange reaction

84
Q

How is chromium (II) ethanoate formed?

A

Orange sodium dichromate (VI) is reduced with zinc in acid solution to form green Cr (III) solution and then to blue Cr (II) solution

Sodium ethanoate mixed with solution and chromium(II) ethanoate red precipitate

Has to be done in inert environment

85
Q

Why does the formation of chromium(II) ethanoate need to be done in an inert environment?

A

Cr2+ is very easily oxidised

Prevents oxygen from oxidising it

86
Q

What is the experimental procedure of the production of chromium(II) ethanoate?

A

Slowly add HCl to a flask with sodium dichromate(VI) and zinc mesh

Once blue colour seen, pinch rubber tube shut so hydrogen cannot escape

Pressure forces Cr2+ through glass tube into flask with sodium dichromate(VI)

Blue solution reacts with sodium ethanoate to form a red precipitate of chromium ethanoate

Filter precipitate and wash with water, then ethanola and ether

All in inert atmosphere

87
Q

What does zinc mesh do in the production of chromium(II) ethanoate?

A

Zinc reduces the dichromate(IV) ions

Reacts with acid to produce hydrogen gas which goes into beaker of water

88
Q

What is ligand exchange?

A

One ligand which can be swapped for another ligand

Causes colour change

89
Q

What occurs to the complex in ligand exchange if the ligands are of similar size?

A

Coordination number and shape doesn’t change

90
Q

What occurs if a uncharged small ligand is substituted for a larger charged ligand?

A

Change of coordination

Change of shape

91
Q

What equilibrium is formed between dichromate(VI) and chromate(VI)?

A

2CrO42- + 2H+ ⇔ Cr2O72- + H2O

Yellow ⇔ orange

92
Q

What is the reaction to reduce dichromate(VI) ion using zinc metal?

A

Cr2O72- + 14H+ + 3Zn → 3Zn2+ + 2Cr3+ + 7H2O

Orange → Green

93
Q

What is the reaction for Cr3+ to form Cr2+?

A

2Cr3+ + Zn → Zn2+ + 2Cr2+

Green → Blue

94
Q

What is the reaction between Cr3+ to form Chromate(VI) ions?

A

2Cr3+ + 10OH- + 3H2O → 2CrO42- + 8H2O

Green → Yellow

95
Q

What occurs to the copper aqueous complex form when reacted with Cl-?

A

[Cu(H2O)6]2+ + 4Cl- → [CuCl4]2- + 6H2O

Pale blue → yellow

96
Q

What is the colour of the aqueous cobalt solution?

A

[Co(H2O)6]2+
Pale pink

97
Q

What is the colour of the copper chloride complex?

A

[CuCl4]2-

Yellow

98
Q

What is the colour of aqueous cobalt chloride?

A

[CoCl4]2-

Blue

99
Q

What is formed when aqueous copper reacts with excess ammonia?

A

[Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 4H2O

Pale blue → Deep blue

100
Q

Why does carbon monoxide poisoning occur because of ligand exchange?

A

Carbon monoxide forms strong dative bond with iron in haemoglobin

Prevents the oxygen from bonidng to the iron and hence it cannot be carried

101
Q

What bonds are broken and formed in ligand exchange?

A

Dative bonds between ligand and metal ion are broken and formed

102
Q

What is the enthalpy change in ligand exchange?

A

Strength of dative bonds broken/formed are of similar strength

Enthalpy change is very small

103
Q

How do the types of ligands affect the likeliness ligand exchange will occur?

A

Poly or bi dentate ligands causes increase of particles in complex

This increases entropy in the complex so more likely to occur

104
Q

What is type of ligand is EDTA?

A

Hexadentate ligand

105
Q

What is a metal-aqua ion?

A

Metal ion complex that only contains water ligands

106
Q

How can you reverse the deprotonation of ligands?

A

Acid

107
Q

What is the reaction between copper aqueous solution and hydroxide ions?

A

[Cu(H2O)6]2+ + 2OH- → [Cu(OH)2(H2O)4] + 2H2O

Pale blue solution → blue precipitate

108
Q

What is the reaction between copper aqueous solution and ammonia?

A

[Cu(H2O)6]2+ + 2NH3 → [Cu(OH)2(H2O)4] + 2NH4+

Pale blue solution → blue precipitate

109
Q

What is the reaction between copper hydroxide and excess ammonia?

A

[Cu(OH)2(H2O)4] + 4NH3 → [Cu(NH3)4(H2O)2]2+ + 2OH- + 4H2O

blue precipitate → deep blue solution

110
Q

What is copper hydroxide?

A

[Cu(OH)2(H2O)4] or Cu(OH)2 (aq)

Solid precipitate

111
Q

What is the reaction between the iron (II) aqueous solution and hydroxide?

A

[Fe(H2O)6]3+ + 3OH- → [Fe(OH)2(H2O)4] + 2H2O

Pale green solution → green precipitate which darkens on standing to orange precipitate

112
Q

What is the colour of the [Fe(OH)2(H2O)4] precipitate?

A

Darkens as oxidised by water and oxygen in air to form iron (III) hydroxide

113
Q

What is the reaction between iron (II) aqueous solution and ammonia?

A

[Fe(H2O)6]2+ + 2NH3 → [Fe(OH)2(H2O)4] + 2NH4+

114
Q

What is the reaction between iron (III) aqueous solution and hydroxide?

A

[Fe(H2O)6]3+ + 3OH- → [Fe(OH)3(H2O)3] + 3H2O

yellow solution → orange precipitate which darkens on standing

115
Q

What is the reaction between iron (III) aqueous solution and ammonia?

A

[Fe(H2O)6]3+ + 3NH3 → [Fe(OH)3(H2O)3] + 3NH4+

yellow solution → orange precipitate which darkens on standing

116
Q

What is the reaction between cobalt (II) aqueous solution and hydroxide?

A

[Co(H2O)6]2+ + 2OH- → [Co(OH)2(H2O)4] + 2H2O

pale pink solution → blue precipitate which turns brown on standing

117
Q

What is the reaction between cobalt (II) and ammonia?
NOT excess

A

[Co(H2O)6]2+ + 2NH3 → [Co(OH)2(H2O)4] + 2NH4+

pale pink solution → blue precipitate which darkens to brown

118
Q

What is the reaction between cobalt hydroxide and excess ammonia?

A

[Co(OH)2(H2O)4] + 6NH3 → [Co(NH3)6]2+ + 2OH- + 4H2O

blue or pink precipitate → yellow-brown solution

oxidises on standing to [Co(NH3)6]3+ ions

119
Q

What is a catalyst?

A

A catalyst is a substance that speeds up a chemical reaction, but is not consumed by the reaction

Lowers the Ea of a reaction

120
Q

Why are transition metlas good catalysts?

A

Change oxidation number by gaining or losing electrons in d-orbitals

Therefore can transfer electrons to speed up reactions

121
Q

What is a homogenous catalyst?

A

Catalysts in the same physical state as the reactants

122
Q

Which phase are homogeneous catalysts usually in?

A

Aqeuous catalyst for a reaction between two aqueous solutions

123
Q

How do homogeneous catalysts usually work?

A

Combines with reactants to form an intermediate species

Intermediate then reacts to form products and reforms the catalyst

124
Q

Why does the formation of an intermediate whilst using homogeneous catalysts increase the rate of reaction?

A

Activation energy neeeded to form intermediates (and products from it) is lower than to make products directly

125
Q

What is autocatalysis?

A

Reaction is catalysed by one of the products which form

126
Q

Why is the reaction between iodide (I-) and peroxodisulphate (S2O82-) slow?

A

Both are negatively charged so they repel each other

Less likely to collide and react

127
Q

What is a heterogeneous catalyst?

A

Catalyst in a different phase from the reactants

128
Q

What are the typical phases when a heterogeneous catalyst is used?

A

Reactants are gases or in solution

Catalyst is a solid

129
Q

Where does a reaction occur on a heterogeneous catalyst?

A

Reaction occurs on the surface of the catalyst

130
Q

Why are transition metals good heterogeneous catalyst?

A

Use partially filled d-orbitals to make weak bonds with the reactant molecules

131
Q

How do heterogeneous catalysts?

A

Reactant molecules attracted and are adsoped onto the surface on the solid catalyst

Catalyst activates molecules so react more easily, weakens the bonds of the reactant causing it to break and the products to form

Product molecules leave surface of catalyst by desorption

132
Q

Why is it important that heterogeneous catalysts do not form strong bonds with the reactants?

A

Prevents the reactants or products formed staying bound to the catalyst

This would mean it cannot be reformed or reused

133
Q

Why does an aqueous complex react with a solution of EDTA4- ions?

A

EDTA is hexadentate, water is monodentate

Increases number of particles as EDTA complex forms

Increase in disorder/entropy

EDTA Complex is therefore more complex

[M(H2O)6] + EDTA → [M(EDTA)] + 6H2O

A Level - Chemistry (26 decks)

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