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AQA A Level Chemistry > transition metals [I2] PAPER 1 > Flashcards

transition metals [I2] PAPER 1 Flashcards

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1
Q

Explain why complexes formed from transition metal ions are coloured.

A

• absorbs wavelengths of visible light, which excites electrons in d-orbitals
• remaining wavelengths of visible light are reflected

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2
Q

Copper(I) iodide is a white solid. Explain why copper(I) iodide is white.

A

• full d shell
• no d-d transitions possible / cannot absorb visible light

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3
Q

what is a transition metal?

A

incomplete d shell

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4
Q

general properties of a transition metal?

A

• form complexes
• form coloured ions
• have variable oxidation states
• good catalysts

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5
Q

what is a ligand?

A

molecule/ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons

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6
Q

what is a complex?

A

a central metal atom/ion surrounded by ligands

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7
Q

what is co-ordination number?

A

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

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8
Q

examples of some monodentate ligands?

A

H2O, NH3, Cl–

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9
Q

why does a change in coordination number arise when the ligands NH3/H2O are exchanged with Cl– ?

A

Cl– ligand is larger than NH3/H2O ligand

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10
Q

examples of bidendate ligands?

A

• H2NCH2CH2NH2
• C2O4–

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11
Q

example of a multidentate ligand?

A

EDTA4–

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12
Q

what is the chelate effect?

A

• bidentate/multidentate ligands replace monodentate ligands in a ligand substitution reaction
• in ligand substitution reactions, a positive entropy change is favoured and is achieved in this way (hence the reaction is more feasible), since it means a more stable complex is formed

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13
Q

example of a complex with multidentate ligands?

A

• haem - iron (II) complex with a multidentate ligand

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14
Q

why is carbon monoxide toxic?

A

• oxygen forms a co-ordinate bond to Fe (II) in haemoglobin, which allows oxygen transport in the blood
• carbon monoxide replaced oxygen that is co-ordinately bonded to Fe (II) in haemoglobin

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15
Q

what shape are the complexes commonly formed by transition metals with small ligands, e.g. H2O and NH3 ?

A

octahedral

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16
Q

octahedral complexes can display _____ isomerism with monodentate ligands

A

cis-trans

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17
Q

octahedral complexes can display _____ isomerism with bidentate ligands

A

optical

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18
Q

what shape are the complexes commonly formed by transition metals with larger ligands, e.g. Cl– ?

A

tetrahedral

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19
Q

Ag+ always forms ____ complexes

A

linear

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20
Q

what complex of Ag+ is used in Tollens’ reagent?

A

[Ag(NH3)2]+

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21
Q

an exchange in ligands in a complex is a ____ reaction

A

ligand substitution

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22
Q

why is the overall enthalpy change for ligand substitution reactions near zero?

A

same/very similar number and type of bond being broken and made

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23
Q

platinum and nickel form ____ complexes, e.g. _____

A

• square planar
• cisplatin

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24
Q

The energy difference between the ground state and the excited state of the d electrons is given by:

A

ΔE = hv = hc/λ

• ΔE = energy difference
• h = Planck’s constant
• c = speed of light
• v = frequency
• λ = wavelength

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25
Q

what can lead to a change in colour of a complex?

A

• change in oxidation state
• change in ligand
• change in co-ordination number

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26
Q

how are different species of vanadium with variable oxidation states formed?

A

oxidation of vanadium by zinc in acidic solution

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27
Q

vanadium oxidation states and colours?

A
28
Q

acidity of transition metal complex ions in aqueous solution?

A

greater charge density of the metal ion means they polarise water molecules more, so more O–H bonds in ligands break to release H+ ions, lowering the pH

29
Q

what is a multidentate ligand?

A

molecule/ion that forms many co-ordinate bonds with the central metal ion

30
Q

what is a bidentate ligand?

A

molecule/ion that forms two co-ordinate bonds with the central metal ion

31
Q

what is a monodentate ligand?

A

molecule/ion that forms one co-ordinate bon with the central metal ion

32
Q
A
33
Q
A
34
Q

Describe how a calibration graph is produced and used to find the concentration of the iron(Ill) complex.

A

• measure absorbance for a range of known concentrations
• plot graph of absorbance (y axis) against concentration (x axis)
• read value of concentration for the measured absorbance from this graph

35
Q
A

B as only one with an incomplete d shell

36
Q
A

A - no lone pair

37
Q
A
38
Q

Solution A contains the compound [Cu(H2O)6]Cl2.
State why the chloride ions in this compound are not considered to be ligands.

A

chloride ions isn’t forming a co-ordinate bond to Cu2+

39
Q
A
40
Q

how can vanadium be reduced from oxidation states 4, to 3, then 2?

A

reduction of vanadate (V) ions by zinc in acidic solution

41
Q

redox titration equations for Fe2+ and C2O4- with MnO4- ?

A
42
Q

what is a heterogeneous catalyst?

A

a catalyst that is in a different phase from the reactants

43
Q

How does iron act as a heterogeneous catalyst in the Haber process?

A

• reactants adsorb onto the surface / active sites of iron
• bonds weaken and the reaction takes place
• products desorb from the surface of the iron

44
Q

factors that affect the lifetime and efficiency of a catalyst?

A

• large surface area by using powder/ small pellets/support medium
• catalyst poisoned (e.g. sulfur binds to the catalyst) - blocks the active site

45
Q
A

two negative ions repel, so activation energy is high

46
Q

Give a reason why Zn2+ ions do not catalyse the reaction.

A

Zn ions have only one oxidation state

47
Q

what colour is MnO4– ?

A

deep purple

48
Q

what colour is Mn2+ ?

A

pink

49
Q

why are transition metals with transition metal compound said to be self-indicating?

A

usually involves a colour change as metal is changing oxidation state

50
Q

what happens to aqua metal ions in acidic conditions?

A

they get reduced

51
Q

what happens to aqua metal ions in alkaline conditions?

A

they get oxidised

52
Q

the redox potential for a transition metal changing from a higher to lower oxidation state is influenced by…

A

• pH
• ligand

53
Q

why are transition metals good catalysts?

A

exist in variable oxidation states, so provide alternative pathways easily

54
Q

advantage of a heterogeneous catalyst?

A

no need for separation of products from the catalyst

55
Q

two reactions in the Contact process, which is catalysed by vanadium (V) oxide, V2O5 ?

A

overall reaction: 2SO2 (g) + O2 (g) → 2SO3 (g)

56
Q

what is a homogeneous catalyst?

A

a catalyst that is in the same phase as the reactants

57
Q

how do homogeneous catalysts work?

A

form intermediates to give a different reaction pathway with a lower activation energy

58
Q
A
59
Q

what is autocatalysis?

A

when the product of the reaction is also a catalyst for the reaction

60
Q
A
61
Q

what is the colour change seen at the end point of a redox titration of Fe2+ with MnO4– ?

A

colourless to pink

62
Q
A

• reactants adsorbed onto platinum surface
• bonds weaken on the surface - reaction occurs
• desorption of the product

63
Q
A
64
Q
A
65
Q
A
66
Q
A

AQA A Level Chemistry (36 decks)

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