Inorganic 2 Section 2 - Unit 23: The Transition Metals Flashcards
State what is meant by the term heterogeneous (1 mark)
- The catalyst is in a different state or phase from the reactants
State three characteristic features of the chemistry of transition metals (3 marks)
- Variable oxidation state
- Act as catalysts
- Form complexes
- Form coloured ions/compounds
Explain what is meant by the term bidentate ligand (1 mark)
- Two atoms that each donate a lone pair (of electrons)
Explain what is meant by the term autocatalysed (1 mark)
A reaction that produces its own catalyst
Describe briefly how colorimetry can be used to determine the concentration of a solution (3 marks)
- 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
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)
- An electron pair on the ligand
- Is donated from the ligand to the central metal ion
Explain, in terms of electrons, why chromium complexes are different colours (6 marks)
- 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
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)
Variable oxidation states
Write two equations to show how vanadium(V) oxide acts as a catalyst in the Contact Process (2 marks)
- V₂O₅ + SO₂ → V₂O₄ + SO3
- V₂O₄ + ½O₂ → V₂O₅
Give one reason why impurities in the reactants can cause problems in processes that use heterogeneous catalysts (1 mark)
Impurities poison / deactivate the catalyst / block the active sites
Explain the meaning of the terms ligand and bidentate as applied to transition metal complexes (2 marks)
- 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)
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)
- Tetrahedral
- [CuCl4]2– / [CoCl4]2–
- Square planar
- (NH3)2PtCl2
- Linear
- [Ag(NH3)2]+
Explain why the Zn2+ ion is not classified as a transition metal ion (1 mark)
- d sub-shell full
In terms of bonding, explain the meaning of the term complex (2 marks)
- Atom or ion bonded to one or more ligands
- By co–ordinate / dative (covalent) bonds
By reference to aqueous copper(II) ions, state the meaning of each of the three terms in the equation ΔE = hv (3 marks)
- ΔE is the energy gained by the (excited) electrons (of Cu2+
- h (Planck’s) constant
- v frequency of light (absorbed by Cu2+(aq))
Give the meaning of the term multidentate (1 mark)
Forms two or more co-ordinate bonds
In terms of electrons, explain why an aqueous solution of cobalt(II) sulfate has a red colour (3 marks)
- (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
“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)
- 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
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)
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-
State the complex formed when solid copper chloride dissolves in water (1 mark)
[Cu(H₂O)₆2+
Define the chelate effect (1 mark)
The substitution of a monodentate ligand with a bidentate or multidentate ligand leads to a more stable complex
Uses of EDTA (2 marks)
- To remove poisonous heavy metal ions from rivers
- To remove Ca2+ present in hard water
State the three factors which can cause a change in colour to arise (3 marks)
- Co-ordination numbers
- Oxidation State
- Ligand
(COLour)
Explain why a change in the ligand or coordination number will alter the colour produced (3 marks)
- Change in the energy split between the d-orbitals
- So change in △E
- And change in the frequency of light absorbed
Explain why scandium’s ion has no colour
- 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
Explain how spectrometry works (2 marks)
- 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
State the use of spectrometry (1 mark)
To determine the concentration of coloured ions
Reduction equation for the use of [Ag(NH₃)₂]+ with CH₃CHO (1 mark)
[Ag(NH₃)₂]+ + e- –> Ag + 2NH₃
Oxidation equation for the use of [Ag(NH₃)₂]+ with CH₃CHO (1 mark)
CH₃CHO + H₂O –> CH₃COOH + 2H+ + 2e-
Colour change for redox titration with manganate ions and iron (II) ions (1 mark)
Purple to Colourless (manganate is in conical flask)
Acid used in manganate titrations (1 mark)
Dilute sulfuric acid
Explain why sometimes, MnO₂ is produced rather than Mn2+ ions during manganate titrations, and how this can affect the titration reading (2 marks
- 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
Explain why HCl is not used to acidify potassium manganate during titrations (1 mark)
- Cl- would be oxidised to Cl₂ (instead of Fe2+ being oxidised)
Explain why HNO₃ is not used to acidify potassium manganate during titrations (3 marks)
- It is an oxidising agent
- So would reduce Fe3+ to Fe2+
- And a lower volume of manganate would be used
Describe the steps involved in heterogenous catalysis (4 marks)
- 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
State which reaction Cr₂O₃ catalyses (1 mark)
Manufacture of methanol from CO + H₂
For a substance to act as a homogenous catalyst, where must its electrode potential lie (1 mark)
- In between the electrode potentials of the two reactants
Reduction and oxidation equations for reaction of S₂O₈²⁻ with I- (2 marks)
S₂O₈²⁻ + 2e⁻ –> 2SO₄²⁻
I- –> I₂ + 2e⁻
Write the equations for the reaction of MnO4- with C2O4-
2Mn³⁺ + C₂O₄²⁻ → 2Mn²⁺ + 2 CO₂
4Mn²⁺ + MnO₄- + 8 H+ → 5Mn³⁺ + 4 H₂O
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)
- 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 /
