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Chemistry > 3.2.5 Transition metals > Flashcards

3.2.5 Transition metals Flashcards

1
Q

What is the definition of a transition metal?

A

Element with an incomplete d sub-shell in atoms/ions

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2
Q

What are the elements of the first transition series?

A

Titanium → copper

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3
Q

What are the electron configurations of the following transition metals:
a) Copper
b) Chromium

A

a) [Ar] 4s^1 3d^10

b) [Ar] 4s^1 3d^5

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4
Q

What are the 4 characteristic properties of transition metals?

A
  1. Form coloured compounds
  2. Act as catalysts
  3. Variable oxidation states
  4. Form complexes
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5
Q

What do the following terms means:
a) Complex
b) Ligand
c) Co-ordination number

A

a) Central metal ion that is surrounded by ligands
b) The molecules which donate a lone pair of electrons to the transition metal ion to form a co-ordinate bond
c) The number of co-ordinate bonds to the central metal ion

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6
Q

Give an example of the following types of ligands:
a) Monodentate
b) Bidentate
c) Polydentate

A

a) Cl-, NH3, H2O, CN-, OH-
b) 1,2-diaminoethane (en) (H2N-CH2-CH2-NH2)
ethandioate ion (ox) (C2O4 ^2-)
c) EDTA ^4-

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7
Q

What property of transition metals allows them to form complexes?

A

Variable oxidation states

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8
Q

What causes a change in coordination number/geometry of the complex during a ligand substitution?

A

Change in size of ligand
eg. NH3 to Cl-

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9
Q

Why would a ligand substitution be incomplete?

A
  • Energetics of the reaction and stability of the products are not favourable
  • Different size ligands
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10
Q

What is the most common arrangement when a transition element ion is in solution?

A

Hexaaqua complex ion
(6 water ligands)

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11
Q

Explain how a haem complex is formed, what are the positives/negatives of the weak co-ordinate bond?

A
  • Oxygen atoms form co-ordinate bond with iron(II)
  • Allows transport of oxygen around body
  • However, oxygen atoms aren’t very good ligands and the co-ordinate bond is weak so oxygen is easily removed from the iron to enter cells
  • Carbon monoxide is a better ligand however, it forms stronger complexes with iron (II)
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12
Q

What is the Chelate effect?

A

When a monodentate ligand is replaced by either a polydentate/bidentate ligand in complex ions.

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13
Q

What 4 shapes of molecules can complexes form?
(Include the bond angle)

A
  • Linear (180°)
  • Tetrehedral (109.5°)
  • Octahedral (90°)
  • Square planar (90°)
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14
Q

Why is the Chelate effect energetically favourable?

A

∆G = ∆H - T∆S
- Relatively small ∆H, reaction between aqueous ions
- Positive ∆S, chelation produces a net increase in the number of particles
- A small ∆H + relative large positive ∆S generally ensures that the overall ∆G is negative

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15
Q

Why is ∆H negligible in most ligand substitution reactions?

A
  • Bonds formed have similar enthalpy to bonds broken
  • Same number of bonds broken and made
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16
Q

What shape of complex is cisplatin an example of?

A

Square planar
(Cl)2-Pt-(NH3)2
90° bond angle

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17
Q

What is the use of cis-platin in medicine, why is trans-platin not used in this way?

A
  • Cancer treatment, binds to DNA in cancer cells
  • Trans-platin has a different arrangement so cannot bind to DNA in the same way
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18
Q

What shape complex is formed when Cl- ions form a complex?

A

Tetrehedral

19
Q

What shape complex is formed when there are 6 co-ordinate bonds?

A

Octahedral complex

20
Q

Which shape complexes form cis-trans isomerism?
Explain the difference between the two isomers?

A

Octahedral and square planar
Cis = Z isomer (same side) or adjacent to eachother
Trans = E isomer or opposite eachother

21
Q

How do optical isomers form in ligand complexes?

A

Octahedral complexes with bidentate ligands

22
Q

How do you calculate the amount of energy absorbed by electrons in a transition element complex?

A

ΔE = h x v

h = Planck’s constant
v = frequency

23
Q

Explain electron promotion and how this produces a coloured complex.

A
  • Electron absorbs light energy which excites it from a 3d orbital of lower energy (ground state) to one of higher energy (excited state)
  • The other frequencies of light which are not absorbed by the electrons combine to make the complimentary colour
24
Q

What do the terms degenerate and non-degenerate orbitals mean?

A

Degenerate = transition ion not bonded to ligands
- 3d orbitals all have equal energy

Non-degenerate = transition ion with co-ordinate bonds to ligands
- 3d orbitals are split into two sets of non-degenerate orbitals with different energy
- This difference in energy is ΔE

25
Q

What factors change the colour of a complex and how?

A

ΔE change caused by change in:
- Co-ordination number
- Ligand
- Oxidation state

26
Q

How can you determine the concentration of coloured ions in a solution?

A

Colorimeter
- Produce a calibration curve, absorption against concentration, by measuring absorption of a set of standard solutions

27
Q

What are the 4 possible oxidation states of vanadium and what colour compounds do they form?

A

+5
VO2^+, yellow

+4
VO^2+, blue

+3
V^3+, green

+2
V^2+, purple

28
Q

How can you illustrate the variable oxidation states of vanadium?
(Write out equations for the oxidation of the Vanadium ions and the reduction of zinc and then combine)

A

Oxidation by zinc in acidic conditions

29
Q

What is the transition metal complex in Tollen’s reagent?
How does it react with aldehydes to produce a silver mirror?

A

[Ag(NH3)2]+

[Ag(NH3)2]+ + e- → Ag (s) + 2NH3 (aq)

30
Q

What are the two common transition metal ion redox titrations which are ‘self-indicating’?

Give the reduction equation and colour change.

A
  1. manganate(VII)
    MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
    purpe → colourless
  2. dichromate(VI)
    Cr2O7^2- + 14H+ + 6e- → 2Cr3+ + 7H2O
    orange → green
31
Q

What is the definition of a heterogeneous and homogeneous catalyst?

A

Heterogeneous = catalyst is in a different physical state (phase) from the reactants

Homogeneous = catalyst is in the same physical state (phase) as the reactants

32
Q

Why are transition elements often used as catalysts?

A
  • Able to form ions with more than one stable oxidation state
  • Vacant d orbitals
33
Q

How do you minimise the cost and maximise the efficiency of a transition metal catalyst (heterogeneous)?

A
  • Increase the SA
  • Only use a thin coat of the catalyst over an inert surface medium
34
Q

Identify a transition metal used in a catalytic converter and state how the converter is constructed to maximise the effect of the catalyst.

A
  • Platinum
  • Deposited on a ceramic honeycomb/mesh which increases the surface area of the catalyst
35
Q

What is the Contact Process and what type of catalysis does it make use of?

Include the equations that involve the catalyst and its regeneration

A

Manufacturing of sulfuric acid
Heterogenous catalysis (V2O5)

  1. SO2 (g) + V2O5 (s) → V2O4 + SO3 (g)
  2. O2 (g) + 2V2O4 (s) → 2V2O5 (s)
36
Q

Describe the steps of catalysis for a hetereogenous catalysit.

A
  1. Adsorption- molecules adhere to the surface of the catalyst
  2. Surface reaction- new bonds form between reactants
  3. Desorption- molecules move away from catalyst surface
37
Q

Describe the steps of catalysis in the Haber Process.

A

Iron = heterogenous catalyst

N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

  1. Nitrogen/hydrogen gas diffuse to the surface of the iron
  2. Adsorption to the surface takes place
  3. The reaction takes place in steps, new bonds form between nitrogen and hydrogen
  4. The ammonia molecule desorbs from the surface
38
Q

What are the limitations of a heterogenous catalyst?

A
  • Impurities can bind to the catalyst active sites and prevent further catalytic action (poisoning of the catalyst)
  • Thin coating will be lost overtime, reducing the efficiency of the catayst
39
Q

What is an example of a homogenous catalyst?
Show the overall equation and seperate steps.

A

S2O8^2- + 2I- → I2 + 2SO4^2-

  1. S2O8^2- + 2Fe^2+ → 2SO4^2- + 2Fe^3+
  2. 2I- + 2Fe^3+ → I2 + 2Fe^2+
40
Q

Explain why and how iron ions catalyse the reaction between iodide ions and S2O8^2- ion.

A
  • 2 negative ions repel eachother which leads to a high Ea and slow reaction
  • Iron able to act because of changes in oxidation state
  • Iron ions provide alternative reaction pathway with lower Ea
41
Q

What is autocataylsis?

A

Product of a reaction can act as a catalyst in the same reaction

42
Q

Give an example of autocatalysis.

A

reaction between manganate(VII) ions and ethandioate ions
Mn2+ = catalyst

MnO4- + 8H+ + 4Mn^2+ → 5Mn^3+ + 4H2O
2Mn^3+ + C2O4^2- → 2Mn^2+ + 2CO2

43
Q

What happens to [MnO4-] during the autocatalysis reaction of manganate(VII) ions and ethandioate ions.

A
  • [MnO4-] decreases as rate of reaction increases due to increase in catalyst Mn2+, which is being produced in the same reaction
  • Rate decreases overtime as more reactents are used up

Chemistry (28 decks)

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