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Chemistry AQA A level > Transition Metals and Aqueous ions > Flashcards

Transition Metals and Aqueous ions Flashcards

1
Q

What is a transition metal?

A

Transition metals are elements in the d-block with an incomplete d-subshell as an atom or ion

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2
Q

What are the 4 characteristic behaviours of transition metals?

A

complex formation (forms a molecule with ligands and a central metal ion)
formation of coloured ions
variable oxidation state
catalytic activity.

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3
Q

What is a ligand?

A

A ligand is a molecule or ion that forms one or more co-ordinate bond with a transition metal by donating a pair of electrons.

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4
Q

What is a complex?

A

A complex is a central metal atom or ion surrounded by ligands.

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5
Q

What’s a ligand substitution reaction?

A

When ligands swap in a chemical reaction.

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6
Q

Co-ordination number

A

The number of co-ordinate bonds to the central metal atom or ion in a complex

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7
Q

What’s useful about the overall charge of a complex?

A

Overall charge can be used to calculate the oxidation state of the metal by looking at the ligands present.

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8
Q

Monodentate ligands

A

Ligands that make one coordinate bond to a metal ion.

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9
Q

Monodentate ligands examples

A

NH3, H2O, and Cl- can act as monodentate ligands.

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10
Q

Cl- as a ligand

A

Cl-is much larger than the O in H2O and the N in NH3 so only 4 Cl- fit around a metal ion where as 6 H2O/NH3 fit around the metal ion.

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11
Q

Bidentate ligand

A

Ligands that can make two coordinate bonds to a metal. You need to know two examples, ethane-1,2-diamine and ethanedioate.

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12
Q

Bidentate ligands example

A

ethane-1,2-diamine (H2NCH2CH2NH2)and ethanedioate. (C2O42–)

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13
Q

Multidentate and examples

A

Ligands that can make more than 2 coordinate bonds to a metal. You need to know EDTA4- and Haem is on the data sheet.

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14
Q

Drawing bidentate ligand with 3 NH2CH2CH2NH2

A
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15
Q

Drawing bidentate ligand with 3 C2O4 2-

A
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16
Q

what determines the shape complexes?

A

Square planar is caused by having a d8 electron configuration.
A complexes’ shape depends on their coordination number:

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17
Q

2 Coordination number ligand shape and bond angle?

A

Linear, 180 degrees

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18
Q

4 coordinate - non d8 metal shape and bond angle

A

Tetrahedral, 109.5

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19
Q

4 coordinate - d8 metal shape and bond angle

A

Square planar, 90 degrees

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20
Q

6 coordinate shape and bond angle

A

Octahedral, 90 degrees

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21
Q

What is cis-trans isomerism?

A

Cis-trans isomerism (similar to E/Z isomers) occur when there are only 2 of one specific monodentate ligand (other ligands can be any type of ligand). The trans isomer the 2 ligands of the same type are 180 degrees away and the cis isomer they are 90 degrees away.

Bidentate ligands in complexes with 2 monodentate ligands can also exhibit cis-trans isomerism

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22
Q

What’s cis platin? how does it funciton?

A

Cisplatin has the structure pictured.
Cis platin the Cl- ligands can be replaced by guanines to bind DNA together.

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23
Q

Optical isomers in complexes

A

Complexes that contain 2/3 bidentate ligands or a multidentate ligand exhibit optical isomerism (non-superimposable mirror image

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24
Q

What is Haemoglobin? How does it work?

A

Haem is an iron(II) complex with a multidentate ligand.
Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.
Carbon monoxide is toxic because it replaces oxygenco-ordinately bonded to Fe(II) in haemoglobin and this coordinate bond is stronger then Fe-O2 so removes this haem from reactions.

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25
Q

Ligand substitution reactions

A

Ligands when added to a solution containing complexes will substitute,
This is powered by entropy creating disorder.

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26
Q

When does complete substitution occur?

A

When a 4 coordinate complex is formed or a multidentate ligand is added

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27
Q

When does partial ligand substitution occur?

A

With an excess of ammonia being added to copper 2+ ions,
When told in the question

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28
Q

Model Answer - Chelate effect

A

When ligands that form more coordinate bonds are substituting
The overall enthalpy change is negligible as the number and type of bonds are similar
There is a significant increase in entropy as the total number of particles increases. (In the reaction above from 4 aqueous particles to 7 aqueous particles.)
This makes the reaction have Gibbs’ free energy change negative so this is highly favoured by entropy and the product is very stable
These ligands can only be substituted by ligands that form more or same number coordinate bonds (mono<bi<multi)

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29
Q

How does colour arise?

A

A portion of visible light of particular frequencies are absorbed to excite d electrons to higher energy levels in the split d orbitals. The frequencies of light that are not absorbed are transmitted to give the substance colour (absorbs opposite colours).

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30
Q

Why are compounds not coloured?

A

Compounds without colour occur because they have completely filled/empty d subshells so can’t absorb visible light

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31
Q

What effects the size of the energy gap/colour of the complex?

A

Colour changes arise from changes in
1. oxidation state
2. co-ordination number
3. ligand

This is because it alters the size of the energy gap

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32
Q

What’s the equation to calculate the size of an energy gap in a complex?

A

ΔE=hv=hc/λ
v =frequency of light absorbed (unit s-1or Hz)
H = Planck’sconstant6.63×10–34(J s)
ΔE=energy gap between split orbitals (J)
c = speed of light (3.00 x 10^8(m s–1)
λ= wavelength of light absorbed (m)

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33
Q

What is colorimetry? What practical steps need to be taken?

A

Colorimetre is a machine that can be used to measure the amount of light being absorbed.
The amount of light absorbed is proportional to the concentration of the solution.
Sometimes the colour change may be hard to detect so a colour intensifying ligand like bipy is added.

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34
Q

How do you create a calibration curve/graph for colorimetry? (model answer)

A

Measure absorbance for a range of known concentrations
Plot graph of concentration vs absorbance
Read value of concentration for the measured absorbance from this graph

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35
Q

What impact does pH and ligand have on oxidation state?

A

Ligands and pH effect the change in oxidation state,
In general it is easier to:
Oxidise a transition metal in alkaline conditions,
Reduce a transition metal in acidic conditions

36
Q

Formula for tollen’s reagent, its use and how it works

A

[Ag(NH3)2]+

Silver mirror formed in presence of aldehydes,

Ag(+1) in [Ag(NH3)2]+ reduced to Ag(0) in silver mirror as the aldehyde is oxidised to a carboxylic acid

37
Q

What happens in the reaction between ammonium vanadate (V) in acid conditions with zinc? Include the colour changes and formulas.

A

Zinc is a reducing agent,
The V is reduced from +5 to +2 and all the way between.
Colour changes: You Better Get Vanadium (Yellow, Blue, Green Violet).
The formulas for the vanadium compounds are in the picture.

38
Q

Redox titrations - Colour changes

A

Redox titrations stop when they go colourless to pale pink

39
Q

Colour MnO4-

A

Purple

40
Q

Half equation for the reduction of Mn in MnO4-

A

MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

41
Q

Reaction of MnO4- with Fe2+

A
42
Q

Reaction of MnO4- and (C2O4)2-

A
43
Q

Scaffold for calculating values in redox titrations

A

Moles known concentration
Molar ratio
Moles unknown concentration
Find the answer

44
Q

Define Heterogenous Catalysis

A

Catalysts that are in a different state to the reactants.

45
Q

How are heterogenous catalysts prepared? Why?

A

Solids and placed on ceramic honeycomb supports to lower the amount of catalyst needed and increase the surface area.

46
Q

Equations for the contact process and what acts as the catalyst?

A

V2O5 is the catalyst,
V2O5 + SO2 –> V2O4 + SO3
V2O4 + ½ O2 –> V2O5
Overall: SO2 + ½ O2 –> SO3

47
Q

How do heterogenous catalysts function? (model answer)

A

1) Reactants adsorbed onto surface onto active sites. This weakens bonds, brings molecules closer and in a more favourable orientation.
2) Reaction takes place.
3)Products are desorbed (leave the surface).

48
Q

How are metals selected for heterogenous catalysis?

A

The best heterogenous catalyst for a reaction. adsorb not too strongly nor too weakly.

49
Q

What is catalyst poisoning?

A

Active sites of heterogenous catalysts can be poisoned as chemicals adsorb onto the active site but cannot desorb so the active site is blocked.

50
Q

Define homogenous Catalysis

A

Catalysts in the same phase as the reactants.

51
Q

Why are reactions with two negative ions slow? (model answer)

A

When the reactants are both negatively charged they repel each other, so the activation energy is high. The catalysts are cations that can attract these anions towards themselves.

52
Q

How do homogenous catalysts work?

A

The catalysts go through an intermediate step. This will involve the catalyst changing oxidation state and returning to its original oxidation state in a second reaction.

Homogenous catalysts must have an electrode potential between the two reactants so it can reduce one and oxidise the other.

53
Q

Equations for the overall reaction between peroxodisulfate (S2O8)2- and I- showing the effect of the catalyst.

A

Overall:
(S2O8)2- + 2I- –> 2(SO4)2- + I2

54
Q

Equations for autocatalysis

A

Overall:
2 MnO4- + 16 H+ + 5 C2O42- → 2 Mn2+ + 8 H2O + 10 CO2

Mn2+ acting as a catalyst:
4 Mn2+ + MnO4– + 8 H+ –> 5 Mn3+ + 4 H2O
2 Mn3+ + C2O42– –> 2 CO2 + 2 Mn2+

55
Q

Describe why autocatalysis is slow and then speeds up.

A

This means the reaction starts off initially slowly as the reactants are both negatively charged they repel each other, so the activation energy is high. When the catalyst is produced the Mn2+ is a cation that can attract these anions towards itself.
This means the rate is initially slow and then speeds up over time.

56
Q

What are hex-aqua ions?

A

Metals that are dissolved in water will form 6 coordinate bonds with water.

57
Q

Iron (II) aqueous ion

A

[Fe(H2O)6]2+
Green solution

58
Q

Copper (II) aqueous ion

A

[Cu(H2O)6]2+
Blue solution

59
Q

Iron (III) aqueous ion

A

[Fe(H2O)6]3+
Purple solution
May look yellow-brown due to some [Fe(H2O)5(OH)]2+ from hydrolysis

60
Q

Aluminium (III) Aqueous ion

A

[Al(H2O)6]3+
Colourless solution

61
Q

Iron (II) aqueous ion with dropwise NaOH

A

[Fe(H2O)4 (OH)2] (s) green ppt goes brown on standing in air

62
Q

mIron (III) aqueous ion with dropwise NaOH

A

[Fe(H2O)3 (OH)3] (s) brown ppt

63
Q

Copper (II) aqueous ion with dropwise NaOH

A

[Cu(H2O)4 (OH)2] (s) blue ppt

64
Q

Iron(II) Aqueous Ion excecss of NaOH after dropwise NaOH

A

No further change

65
Q

Aluminium (III) aqueous ion with dropwise NaOH

A

[Al(H2O)3 (OH)3] (s) white ppt

66
Q

Iron(III) Aqueous Ion excecss of NaOH after dropwise NaOH

A

No further change

67
Q

Copper(II) Aqueous Ion excecss of NaOH after dropwise NaOH

A

No further change

68
Q

Aluminium(III) Aqueous Ion excecss of NaOH alone/after dropwise NaOH

A

[Al(OH)4]- colourless solution
Al(OH)3(OH)3 is amphoteric

69
Q

Amphoteric

A

A compound that can act as an acid or base

70
Q

Iron(II) Aqueous Ion with dropwise ammonia

A

Fe(H2O)4 (OH)2 green ppt goes brown on standing in air

71
Q

Iron(III) Aqueous Ion with dropwise ammonia

A

[Fe(H2O)3 (OH)3] (s) brown ppt (ppt may look orange-brown)

72
Q

Aluminium(III) Aqueous Ion with dropwise ammonia

A

[Al(H2O)3 (OH)3] (s) white ppt

73
Q

Copper(II) Aqueous Ion with dropwise ammonia

A

[Cu(H2O)4 (OH)2] (s) blue ppt

74
Q

Copper(II) Aqueous Ion with excess ammonia alone/ after dropwise ammonia

A

[Cu(H2O)2 (NH3 ) 4 ] 2+(aq) deep blue solution

75
Q

Iron(II) Aqueous Ion with excess ammonia after dropwise ammonia

A

No further change

76
Q

Iron(III) Aqueous Ion with excess ammonia after dropwise ammonia

A

No further change

77
Q

Aluminium(III) Aqueous Ion with excess ammonia after dropwise ammonia

A

No further change

78
Q

[VO2]+/[VO2(H20)4]+

A

Oxidation state 5
yellow

79
Q

[VO]2+/[VO(H2O)5]2+

A

Oxidation state +4
blue

80
Q

[V(H2O)6 ] 3+/V3+

A

Oxidation state +3
green

81
Q

[V(H2O)6]2+/V2+

A

Oxidation State +2
Purple

82
Q

Na2CO3(aq) with iron (II)

A

FeCO3 (s) green ppt

83
Q

Na2CO3(aq) with iron (III)

A

Fe(H2 O)3 (OH)3 (s) brown ppt (ppt may look orange-brown) and CO2 gas evolved

84
Q

Na2CO3(aq) with copper (II)

A

CuCO3 (s) blue-green ppt

85
Q

Na2CO3(aq) with aluminium (III)

A

Al(H2 O)3 (OH)3 (s) white ppt and CO2 gas evolved

86
Q

What’s the generic equation for M3+ and M2+ aqua ions to show they are acids?

A
87
Q

Why are M3+ ions more acidic than M2+ ions? (Model answer/key phrases)

A

The acidity of [M(H2O)6]3+ is greater than that of [M(H2O)6]2+ because the 3+ metal ions have higher charge density (charge/size ratio).
M3+ ions are more polarising so polarise water molecules more.
This weakens the O-H bond so it breaks more easily releasing H+ ions

Chemistry AQA A level (11 decks)

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