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Chemistry > I2: 23 The Transition Metals > Flashcards

I2: 23 The Transition Metals Flashcards

1
Q

Why do the transition metals have their characteristics?

A

Due to their incomplete d sub-level in atoms or ions.

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2
Q

List the characteristics of the transition metals.

A
  • complex formation
  • formation of coloured ions
  • variable oxidation state
  • catalytic activity
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3
Q

What is the definition of a transition metal?

A

A metal that forms one or more stable ions with a partially filled d sub-level.

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4
Q

What are the physical properties of the transition metals?

A
  • high density
  • high mp and bp
  • almost the same ionic radii
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5
Q

What is the definition of a ligand?

A

A molecule or 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 the definition of a complex?

A

A central metal atom or ion surrounded by ligands, co-ordinately bonded to it..

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7
Q

What is the definition of a co-ordination number?

A

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

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8
Q

What are common monodentate ligands?

A
  • H2O
  • NH3
  • Cl-
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9
Q

What are the similar characteristics of H2O and NH3?

A
  • similar in size
  • uncharged
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10
Q

How does the co-ordination number change when NH3 and H2O are exchanged?

A

No change.

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11
Q

How is the Cl- ligand different to H2O and NH3?

A

Cl- is larger

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12
Q

What happens to the co-ordination number when H2O and Cl- are exchanged?

A

It may change.

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13
Q

What are bidentate ligands?

A

Ligands that can form two co-ordinate bonds.

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14
Q

What are multidentate ligands?

A

Ligands that can form more than one co-ordinate bond.

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15
Q

What is haem?

A

An iron(II) complex with a multidentate ligand.

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16
Q

What allows oxygen to be transported in the blood?

A

Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin.

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17
Q

Why is carbon monoxide toxic?

A

It replaces oxygen (co-ordinately bonded to Fe(II) in haemoglobin).

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18
Q

What is the chelate effect?

A

When bidentate and multidentate ligands replace monodentate ligands from complexes.

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19
Q

Explain the chelate effect.

A

The enthalpy change for a ligand exchange reaction is usually very small.
Ligand exchange reactions are reversible but the equilibrium lies so far to the right as complexes with multidentate ligands are much more stable.

The increase in stability is the chelate effect - it’s why multidentate ligands always form much more stable complexes than monodentate ligands.

When monodentate ligands are substituted with multidentate ligands, the number of particles in solution increases - the entropy increases. Reactions that result in an increase in entropy are more likely to occur.

It’s difficult to reverse these reactions because it would cause a decrease in entropy.

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20
Q

What shape complex do transition metal ions commonly form with small ligands?

A

Octahedral complexes.

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21
Q

What can octahedral complexes with monodentate ligands display?

A

Cis-trans isomerism.

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22
Q

What can octahedral complexes with bidentate ligands display?

A

Optical isomerism.

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23
Q

What shape complex do transition metals with larger ligands form?

A

Tetrahedral complexes.

24
Q

What are all the shape complexes that transition metals commonly form?

A
  • octahedral complex
  • tetrahedral complex
  • square planar complex
25
Q

What can square planar complexes display?

A

Cis-trans isomerism.

26
Q

Which isomer is cisplatin?

A

Cis isomer.

27
Q

What complex does Ag+ form?

What shape, formula, and use?

A

The linear complex - [Ag(NH3)2]+

Used in Tollen’s reagent.

28
Q

How can transition metal ions be identified?

A

By their colour.

29
Q

How does colour arise?

A

When some of the wavelengths of visible light are absorbed and the remaining wavelengths of light are transmitted or reflected.

30
Q

What happens to d electrons when light is absorbed?

A

They move from the ground state to an excited state.

31
Q

What is the equation for the energy difference between the ground state and the excited state of d electrons?

A

change in E = hv = hc / wavelength

h - Planck’s constant (J s)
v - frequency (Hz)
c - speed of light (m s-1)

32
Q

What factors can lead to a change in colour of transition metal ions?

A
  • change in oxidation state
  • change in co-ordination number
  • change in ligand
33
Q

Why can a transition metal ion’s colour change?

A

The energy gap between the ground state and excited state of d electrons changes.

34
Q

What is used in spectroscopy?

A

The absorption of visible light.

35
Q

What can a simple colorimeter be used for?

A

To determine the concentration of coloured ions in solution.

36
Q

How are vanadium species (with oxidation states IV, III, and II) formed?

(VO)2+, V3+, V2+

A

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

(VO2)+ = vanadate (V)

37
Q

What is a redox potential?

A

The same as electrode potentials.
Tells you how easily an atom or ion is reduced to a lower oxidation state.

38
Q

What factors affect the redox potential for a transition metal ion?

A
  • pH
  • type of ligand
39
Q

In what solution would redox potentials be larger?

What does it mean when the redox potential is larger?

A

More acidic solutions.
The ion is more easily reduced.

40
Q

What is the reduction of Tollen’s reagent used for?

A

To distinguish between aldehydes and ketones.

41
Q

What is the equation for the reaction of Fe2+ and MnO4-?

A

MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O

42
Q

What is the equation for the reaction between C2O42- and MnO4-?

A

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

43
Q

What is the process of a redox titration?

A
  1. Measure out a quantity of reducing agent (e.g. Fe2+, C2O42-) and put it in a conical flask.
  2. Add excess dilute sulfuric acid to the flask (~20cm3).
  3. Add the oxidising agent (e.g. purple MnO4-) to the conical flask using a burette, swirling as you go.
  4. Stop when the mixture in the flask just becomes the colour of the oxidising agent (or decolourises).
  5. Repeat until you get concordant titrations.
44
Q

What types of catalyst can transition metals and their compounds act as?

A

Heterogenous and homogenous catalysts.

45
Q

What is a heterogenous catalyst?

A

A catalyst which is in a different phase from the reactants and the reaction occurs at active sites on the surface.

46
Q

What are support mediums used for in heterogenous catalysts?

A

To maximise the surface area and minimise the cost.

47
Q

What catalyst is used in the Contact process?

Also what type of catalyst, and what is produced in the Contact process.

A

Heterogenous catalyst vanadium(V) oxide, V2O5(s).

For making sulfuric acid.

48
Q

What catalyst is used in the Haber process?

Also what type of catalyst, and what is produced in the Haber process.

A

Heterogenous catalyst Fe.

For making ammonia.

49
Q

How can heterogenous catalysts become poisoned?

A

Impurities block the active sites (which reactants normally adsorb onto).
The catalyst has reduced efficiency which has a cost implication.

50
Q

What is a homogenous catalyst?

A

A catalyst which is in the same phase as the reactants.

51
Q

When catalysts and reactants are in the same phase, what does the reaction proceed through?

A

An intermediate species.

52
Q

Explain the importance of variable oxidation states in catalysis.

A

Transition metals make good catalysts because they can change oxidation states by gaining or losing d electrons.
They can transfer electrons to speed up reactions.

53
Q

Explain, with the aid of equations, how V2O5 acts as a catalyst in the Contact process.

A

V2O5 + SO2 -> V2O4 + SO3
V2O4 + 0.5O2 -> V2O5

SO2 + 0.5O2 -> SO3

54
Q

Explain, with the aid of equations, how Fe2+ ions catalyse the reaction between I- and S2O82-.

A

S2O82- + 2Fe2+ -> 2Fe3+ + 2SO42-
2Fe3+ + 2I- -> I2 + 2Fe2+

S2O82- + 2I- -> I2 + 2SO42-

55
Q

Why is the reaction between I- and S2O82- slow? Why does Fe2+ speed the reaction up?

A

Both ions are negatively charged so they repel eachother, making it unlikely that they’ll collide and react.

Fe2+ is positive so there’s no repulsion in each step of the reaction.

56
Q

Explain, with the aid of equations, how Mn2+ ions autocatalyse the reaction between C2O42- and MnO4-.

A

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

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

57
Q

What is autocatalysis?

A

When the product of a reaction acts as a catalyst for the reaction.
So as the reaction progresses, the amount of product increases, so the reaction speeds up.

Chemistry (33 decks)

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