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Chemistry > Transition metals > Flashcards

Transition metals Flashcards

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1
Q

ligand

A

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

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2
Q

complex

A

central metal atom or ion surrounded by ligands.

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3
Q

co-ordination number

A

number is number of co-ordinate bonds to the central metal atom or ion.

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4
Q

transition metal

A

incomplete d sub-level in atoms or ions

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5
Q

monodentate

A

(e.g. H2O, NH3 and Cl- ) which can form one coordinate bond per ligand

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6
Q

bidentate

A

(e.g. NH2CH2CH2NH2 and ethanedioate ion C2O4 2- ) which have two atoms with lone pairs and can form two coordinate bonds per ligand

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7
Q

multidentate

A

(e.g. EDTA4- which can form six coordinate bonds per ligand).

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8
Q

[Co(H2O)6]2+(aq) + 6NH3 (aq)

A

[Co(H2O)6]2+(aq) + 6NH3 (aq) -> [Co(NH3)6]2+(aq) + 6H2O (l)

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9
Q

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

A

[Cu(H2O)6]2+(aq) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)

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10
Q

Cl-

A

The Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number.

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11
Q

[CuCl4]2-

A

yellow/green solution

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12
Q

[CoCl4]2-

A

blue solution

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13
Q

[Cu(H2O)6]2+ +2C2O42-

A

[Cu(C2O4)2(H2O)2]2- +4H2O

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14
Q

Chelate effect

A

substitution of monodentate ligand with a bidentate or a multidentate ligand leads to a more stable complex.

increased entropy

Free energy ΔG will be negative as ΔS is positive and ΔH is small

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15
Q

Tollens

A

[Ag(NH3)2]+

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16
Q

colour changes arise from

A
  1. oxidation state,
  2. co-ordination number
  3. ligand
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17
Q

how does colour change arise

A

Colour arises from electronic transitions from the ground state to excited states: between different d orbitals.
A portion of visible light is absorbed to promote d electrons to higher energy levels. The light that is not absorbed is transmitted to give the substance colour.

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18
Q

ΔE=hv=hc/λ

A 
v = frequency of light absorbed (unit s-1 or Hz) 
H = Planck’s constant 6.63 × 10–34 (J s)
E = energy difference between split orbitals (J) 
c = speed of light 3.00 x 108 (m s–1)
λ = wavelength of light absorbed (m)
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19
Q

Sc

A

Scandium is a member of the d block. Its ion (Sc3+) hasn’t got any d electrons left to move around. So there is not an energy transfer equal to that of visible light.

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20
Q

spectroscopy

A

The amount of light absorbed is proportional to the concentration of the absorbing species (and to the distance travelled through the solution).
Some complexes have only pale colours and do not absorb light strongly. In these cases a suitable ligand is added to intensify the colour.

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21
Q

spectroscopy method

A
  • Add an appropriate ligand to intensify colour
  • Make up solutions of known concentration
  • Measure absorption or transmission
  • Plot graph of absorption vs concentration
  • Measure absorption of unknown and compare
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22
Q

coloured filter

A

The colour of the filter is chosen to allow the wavelengths of light through that would be most strongly absorbed by the coloured solution.

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23
Q

trends in oxidation states

A
  • Relative stability of +2 state with respect to +3 state increases across the period
  • Compounds with high oxidation states tend to be oxidising agents e.g MnO4-
  • Compounds with low oxidation states are often reducing agents e.g V2+ & Fe2+
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24
Q

VO2 +

A

Oxidation state +5 ( a yellow solution)

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25
Q

VO 2+

A

Oxidation state + 4 (a blue solution)

26
Q

V 3+

A

Oxidation state + 3 (a green solution)

27
Q

V 2+

A

Oxidation state + 2 (a violet solution)

28
Q

Tollens’ reaction

A

Red
[Ag(NH3)2]+ + e- -> Ag +2NH3

Ox
CH3CHO + H2O->CH3CO2H + 2H+ + 2e-

29
Q

NH3 and H2O

A

similar size

uncharged

30
Q

Catalyst

A

Catalysts increase reaction rates without getting used up. They do this by providing an alternative route with a lower activation energy

31
Q

heterogenous catalyst

A

different phase from the reactants

32
Q

homogenous catalyst

A

same phase as the reactants

33
Q

Strength of adsorption

A

The strength of adsorption helps to determine the effectiveness of the catalytic activity.
Some metals e.g. W have too strong adsorption and so the products cannot be released.
Some metals e.g. Ag have too weak adsorption, and the reactants do not adsorb in high enough concentration.
Ni and Pt have about the right strength and are most useful as catalysts.

34
Q

adsorption

A

Adsorption of reactants at active sites on the surface may lead to catalytic action. The active site is the place where the reactants adsorb on to the surface of the catalyst. This can result in the bonds within the reactant molecules becoming weaker, or the molecules being held in a more reactive configuration. There will also be a higher concentration of reactants at the solid surface, so leading to a higher collision frequency.

35
Q

steps in heterogeneous catalysis

A
  1. Reactants form bonds with atoms at active sites on the surface of the catalyst (adsorbed onto the surface)
  2. As a result bonds in the reactants are weakened and break
  3. New bonds form between the reactants held close together on catalyst surface.
  4. This in turn weakens bonds between product and catalyst and product leaves (desorbs).
36
Q

V2O5

A

heterogeneous catalyst in the Contact process.

Overall equation : 2SO2 + O2 -> 2SO3

step1 SO2 +V2O5 ->SO3 + V2O4

step 2 2V2O4 + O2 -> 2V2O5

37
Q

Fe

A

Fe is used as a heterogeneous catalyst in the Haber process.

N2 + 3H2 ->2NH3

38
Q

poisoning of heterogeneous

A

Heterogeneous catalysts can become poisoned by impurities that block the active sites and consequently have reduced efficiency; this has a cost implication.

e.g. poisoning by sulfur in the Haber process and by lead in catalytic converters in cars means that catalysts lose their efficiency and may need to be replaced.

39
Q

Cr2O3

A

hetrogenous catalyst is used in the manufacture of methanol from carbon monoxide and hydrogen.
CO + 2H2 ->CH3OH

40
Q

Fe2+

A

homogenous catalyst

reaction is slow as both are negative
S2O8 2-(aq) + 2I-(aq) -> I2(aq) + 2SO4 2-(aq)

Step 1
S2O8 2- + 2Fe2+ -> 2Fe3+ + 2SO4 2-

Step 2
2Fe3+ + 2I- -> I- + 2Fe2+

41
Q

Autocatalysis

A

When a product catalyses the reaction

overall
2 MnO4- + 5 C2O42- + 16 H+ ->2Mn2+ + 10 CO2 + 8 H2O

Step 1
4Mn2+ + MnO4- + 8 H+ -> 5Mn3+ + 4 H2O
Step 2
2Mn3+ + C2O42- -> 2Mn2+ + 2 CO2

42
Q

Autocatalysis reaction

A

The initial uncatalysed reaction is slow because the reaction is a collision between two negative ions which repel each other leading to a high activation energy.
The Mn2+ ions produced act as an autocatalyst and therefore the reaction starts to speed up because they bring about the alternative reaction route with lower activation energy. ThereactioneventuallyslowsastheMnO4- concentrationdrops.

43
Q

Silver

A

Silver behaves like the transition metals in that it can form complexes and can show catalytic behaviour (although it adsorbs too weakly for many examples).

Silver is unlike the transition metals in that it does not form coloured compounds and does not have variable oxidation states.

Silver complexes all have a +1 oxidation state with a full 4d subshell (4d10). As it is 4d10 in both its atom and ion, it does not have a partially filled d subshell and so is not a transition metal by definition. It is not therefore able to do electron transitions between d orbitals that enable coloured compounds to occur.

44
Q

[Ag(NH3)2]+ + NaBr

A

AgBr

cream ppt

45
Q

AgBr + Conc NH3

A

[Ag(NH3)2]+

colourless solution

46
Q

AgCl + Dilute NH3

A

[Ag(NH3)2]+

47
Q

[Ag(H2O)2]+ (colourless) + NaCl

A

AgCl

White ppt

48
Q

[Ag(H2O)2]+ + Dilute NH3

A

[Ag(NH3)2]+

49
Q

Ag + Conc HNO 3

A

[Ag(H2O)2]+

50
Q

[Ag(NH3)2]+ + aldehyde

A

Ag

51
Q

AgCl dissolving

A

AgCl(s) + 2NH3(aq) -> [Ag(NH3)2]+ (aq) + Cl- (aq)

52
Q

Tollens reactions

A

Red : [Ag(NH3)2]+ + e- -> Ag +2NH3

Ox : CH3CHO + H2O -> CH3CO2H + 2H+ + 2e-

53
Q

Cr3+

A

green/violet

54
Q

Cr2O7 2-

A

Orange

55
Q

Mn2+

A

pale pink

56
Q

MnO4 -

A

Purple

57
Q

Fe 2+

A

pale green

58
Q

Fe 3+

A

yellow

59
Q

Co 2+

A

pink

60
Q

Ni 2+

A

green

61
Q

Cu 2+

A

blue

Chemistry (33 decks)

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