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AQA A Level Chemistry > Inorganic 2 Section 2 - Unit 23: The Transition Metals > Flashcards

Inorganic 2 Section 2 - Unit 23: The Transition Metals Flashcards

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1
Q

State what is meant by the term heterogeneous (1 mark)

A
  • The catalyst is in a different state or phase from the reactants
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2
Q

State three characteristic features of the chemistry of transition metals (3 marks)

A
  • Variable oxidation state
  • Act as catalysts
  • Form complexes
  • Form coloured ions/compounds
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3
Q

Explain what is meant by the term bidentate ligand (1 mark)

A
  • Two atoms that each donate a lone pair (of electrons)
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4
Q

Explain what is meant by the term autocatalysed (1 mark)

A

A reaction that produces its own catalyst

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5
Q

Describe briefly how colorimetry can be used to determine the concentration of a solution (3 marks)

A
  • Make some known concentrations (of the coloured solution and read the absorbance of each one using a colorimeter)
  • Plot a graph of absorbance vs concentration
  • Compare unknown concentration from calibration curve
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6
Q

A co-ordinate bond is formed when a transition metal ion reacts with a ligand.
Explain how this co-ordinate bond is formed (2 marks)

A
  • An electron pair on the ligand

- Is donated from the ligand to the central metal ion

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7
Q

Explain, in terms of electrons, why chromium complexes are different colours (6 marks)

A
  • In each of the complexes, the oxidation state of Cr is +3
  • And the electron configuration is the same
  • But ligands are different
  • Different different split of (d) electron energy levels
  • Different wavelengths / colours (of light) are absorbed
  • Different wavelengths / colours (of light) are
    transmitted
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8
Q

State the general property of transition metals that allows the vanadium in vanadium(V) oxide to act as a catalyst in the Contact Process (1 mark)

A

Variable oxidation states

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9
Q

Write two equations to show how vanadium(V) oxide acts as a catalyst in the Contact Process (2 marks)

A
  • V₂O₅ + SO₂ → V₂O₄ + SO3

- V₂O₄ + ½O₂ → V₂O₅

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10
Q

Give one reason why impurities in the reactants can cause problems in processes that use heterogeneous catalysts (1 mark)

A

Impurities poison / deactivate the catalyst / block the active sites

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11
Q

Explain the meaning of the terms ligand and bidentate as applied to transition metal complexes (2 marks)

A
  • A ligand is an electron pair / lone pair donor
  • A bidentate ligand donates two electron pairs (to a transition metal ion) from different atoms / two atoms (on the same molecule / ion)
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12
Q

Other than octahedral, there are several different shapes shown by transition metal complexes. Name three of these shapes and for each one give the formula of a complex with that shape (6 marks)

A
  • Tetrahedral
  • [CuCl4]2– / [CoCl4]2–
  • Square planar
  • (NH3)2PtCl2
  • Linear
  • [Ag(NH3)2]+
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13
Q

Explain why the Zn2+ ion is not classified as a transition metal ion (1 mark)

A
  • d sub-shell full
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14
Q

In terms of bonding, explain the meaning of the term complex (2 marks)

A
  • Atom or ion bonded to one or more ligands

- By co–ordinate / dative (covalent) bonds

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15
Q

By reference to aqueous copper(II) ions, state the meaning of each of the three terms in the equation ΔE = hv (3 marks)

A
  • ΔE is the energy gained by the (excited) electrons (of Cu2+
  • h (Planck’s) constant
  • v frequency of light (absorbed by Cu2+(aq))
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16
Q

Give the meaning of the term multidentate (1 mark)

A

Forms two or more co-ordinate bonds

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17
Q

In terms of electrons, explain why an aqueous solution of cobalt(II) sulfate has a red colour (3 marks)

A
  • (Blue) light is absorbed (from incident white light)
  • Due to electrons moving to higher levels/electrons excited
  • Red light (that) remains (is transmitted)/light that remains (transmitted light) is the colour observed
18
Q

“The strength of adsorption onto the active sites on the surface of a heterogeneous catalyst helps to determine the activity of the catalyst.”

Explain how heterogeneous catalysts work, give one example of a reaction catalysed in this way and discuss why different catalysts have different activities (8 marks)

A
  • Increased collision frequency
  • Reactants must be correctly orientated
  • Reaction on the surface
  • Products desorbed
  • Haber Process
  • Catalyst is Fe
  • If absorption too weak reactants not brought together
  • If adsorption too strong products not desorbed
19
Q

Transition metal complexes have different shapes and many show isomerism. Describe the different shapes of complexes and show how they lead to different types of isomerism. (5 marks)

A

Shapes of complexes:

  • Octahedral
  • Square planar

Cis/Trans isomerism:
- Cis/trans in both square planar and octahedral complexes

Optical isomerism:

  • Optical isomerism in octahedral complexes
  • Occurs with specific bidentate ligands such as [C2O4]2-
20
Q

State the complex formed when solid copper chloride dissolves in water (1 mark)

A

[Cu(H₂O)₆2+

21
Q

Define the chelate effect (1 mark)

A

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

22
Q

Uses of EDTA (2 marks)

A
  • To remove poisonous heavy metal ions from rivers

- To remove Ca2+ present in hard water

23
Q

State the three factors which can cause a change in colour to arise (3 marks)

A
  • Co-ordination numbers
  • Oxidation State
  • Ligand

(COLour)

24
Q

Explain why a change in the ligand or coordination number will alter the colour produced (3 marks)

A
  • Change in the energy split between the d-orbitals
  • So change in △E
  • And change in the frequency of light absorbed
25
Q

Explain why scandium’s ion has no colour

A
  • Its ion has a 3+ charge
  • So there are no more d electrons left to move around
  • So there is no energy transfer equal to that of visible light
26
Q

Explain how spectrometry works (2 marks)

A
  • When visible light of increasing frequency is pass through a sample of a coloured complex ion, some light is absorbed
  • The amount absorbed is proportional to the concentration of the absorbing species
27
Q

State the use of spectrometry (1 mark)

A

To determine the concentration of coloured ions

28
Q

Reduction equation for the use of [Ag(NH₃)₂]+ with CH₃CHO (1 mark)

A

[Ag(NH₃)₂]+ + e- –> Ag + 2NH₃

29
Q

Oxidation equation for the use of [Ag(NH₃)₂]+ with CH₃CHO (1 mark)

A

CH₃CHO + H₂O –> CH₃COOH + 2H+ + 2e-

30
Q

Colour change for redox titration with manganate ions and iron (II) ions (1 mark)

A

Purple to Colourless (manganate is in conical flask)

31
Q

Acid used in manganate titrations (1 mark)

A

Dilute sulfuric acid

32
Q

Explain why sometimes, MnO₂ is produced rather than Mn2+ ions during manganate titrations, and how this can affect the titration reading (2 marks

A
  • Produced when the solution isn’t acidic enough (less H+ available)
  • So brown MnO₂ produced which will mask the colour change
  • And leader to a greater volume of MnO4- being used
33
Q

Explain why HCl is not used to acidify potassium manganate during titrations (1 mark)

A
  • Cl- would be oxidised to Cl₂ (instead of Fe2+ being oxidised)
34
Q

Explain why HNO₃ is not used to acidify potassium manganate during titrations (3 marks)

A
  • It is an oxidising agent
  • So would reduce Fe3+ to Fe2+
  • And a lower volume of manganate would be used
35
Q

Describe the steps involved in heterogenous catalysis (4 marks)

A
  • Reactants adsorbed onto active sites on the surface
  • As a result, bonds in the reactants are weakened and break
  • New bonds form between the reactants held close together on the catalyst surface
  • This in turn weakens the bonds between the products and the catalyst and so the product is desorbed
36
Q

State which reaction Cr₂O₃ catalyses (1 mark)

A

Manufacture of methanol from CO + H₂

37
Q

For a substance to act as a homogenous catalyst, where must its electrode potential lie (1 mark)

A
  • In between the electrode potentials of the two reactants
38
Q

Reduction and oxidation equations for reaction of S₂O₈²⁻ with I- (2 marks)

A

S₂O₈²⁻ + 2e⁻ –> 2SO₄²⁻

I- –> I₂ + 2e⁻

39
Q

Write the equations for the reaction of MnO4- with C2O4-

A

2Mn³⁺ + C₂O₄²⁻ → 2Mn²⁺ + 2 CO₂

4Mn²⁺ + MnO₄- + 8 H+ → 5Mn³⁺ + 4 H₂O

40
Q

The complex ion formed in aqueous solution between cobalt(II) ions and chloride ions is a different colour from the [Co(H2O)6]2+ ion. Explain why these complex ions have different colours (6 marks)

A
  • In different complexes the d orbitals / d electrons (of the cobalt) will have different energies / d orbital splitting will be different
  • Light / energy is absorbed causing an electron to be excited
  • Different wavelength / colour of light will be absorbed /

AQA A Level Chemistry (18 decks)

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