100
Foundation
Foundation
What is the definition of a transition metal?
Forms at least one stable ion with a partially filled d‑subshell.
What is the formula of the hexaaquairon(III) ion.
[Fe(H2O)6]3+
State two typical properties of transition metals.
They form coloured ions, have variable oxidation states, act as catalysts, and form complex ions.
What is a ligand?
A species that donates a lone pair to a metal ion to form a coordinate bond
What colour is [Cu(H2O)6]2+ in aqueous solution?
blue
What is a monodentate ligand? Give one example.
A ligand donating one lone pair; e.g. H₂O, NH₃, Cl⁻.
Describe the colour change when excess NH₃ is added to aqueous Cu²⁺.
Pale blue solution → deep blue solution.
What colour precipitate forms when OH⁻ is added to Fe³⁺(aq)?
Brown Fe(OH)₃ precipitate.
What is the shape of the complex [CuCl4]2-?
Tetrahedral
What kind of ligand is ethane‑1,2‑diamine, C₂O₄²⁻?
bidentate ligand
Write the equation for the reaction between from aqueous Fe²⁺ and dropwise OH⁻.
Fe²⁺ + 2OH⁻ → Fe(OH)₂(s)
[Fe(H2O)6]²⁺ + 2OH⁻ → Fe(H2O)4(OH)₂(s)
Describe what happens when excess chloride ions are added to [Cu(H2O)6]2+ .Include the colour change and any coordination number changes.
Chloride ions replace water ligands
The complex changes from blue [Cu(H2O)6]2+ to yellow‑green [CuCl4]2-.
Coordination number changes from 6 to 4.
Describe the ligand substitution when [Cr(H2O)6]3+ reacts with excess NH₃. (Colour changes and formulae of products)
Green precipitate of Cr(OH)₃ forms → dissolves in excess ammonia to give a violet/purple [Cr(NH3)6]3+
Describe what happens when excess ammonia is added to [Cu(H2O)6]2+. Include the intermediate and final colours.
In dropwise: pale blue precipitate of Cu(OH)₂.
In excess:precipitate dissolves, form deep blue complex [Cu(NH3)4(H2O)2]2+
Explain why Cu(H2O)2(NH3)4]2+ displays Jahn-Teller Distortion in its geometry
Cu-O are WEAKER and so are LONGER
Cu-N are STRONGER and so are SHORTER
H2O poorer ligand than NH3
The shape is slightly distorted
For the complex [M(en)2Cl2], state the denticity of “en” and the coordination number.
Write the reduction half‑equation for MnO₄⁻ in acidic conditions.
MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
Why is cis‑platin effective as an anticancer drug, but trans‑platin is not?
The cis form binds to adjacent DNA bases → cross-links DNA → prevents replication.
The trans form cannot bind both sites.
Predict and explain the change in coordination number when [Cu(H2O)6]2+ reacts with concentrated chloride ions.
The coordination number decreases from 6 to 4 because chloride ions are larger ligands than water and cannot pack six around the Cu²⁺ ion without strong repulsion.
So from octahedral it becomes tetrahedral
Draw cis -[Ni(NH2CH2CH2NH2)2(H2O)2]2+
H2O ligands are 90o to each other
In an experiment, a solution of Fe²⁺ is titrated with acidified MnO₄⁻. Explain why MnO₄⁻ must be acidified, and describe what would happen if the solution were neutral instead.
MnO₄⁻ is a strong oxidising agent only in acidic solution, where it is reduced to Mn²⁺.
In neutral or weakly alkaline solution, MnO₄⁻ is reduced only to MnO₂(s), forming a brown precipitate.
This would cause the titration to give inaccurate results because the reaction pathway and stoichiometry change.
A student adds excess concentrated hydrochloric acid to a solution of [Co(H2O)6]2+, forming [CoCl4]2-. The student suggests this is simply a redox reaction. Explain why this statement is incorrect.
No electrons are transferred: the oxidation state of cobalt remains +2 throughout.
The reaction is a ligand substitution, where water ligands are replaced by chloride ions.
Explain why the hexaaquairon(III) ion, [Fe(H2O)6]3+, releases protons more readily than the hexaaquairon(II) ion, [Fe(H2O)6]2+
Fe³⁺ has a much higher charge density, which strongly polarises the O–H bonds in the coordinated water molecules.
This weakens the O–H bond, making proton release easier.
Therefore, [Fe(H2O)6]3+ is significantly more acidic than [Fe(H2O)6]2+
A transition metal complex displays optical isomerism even though all of its ligands are identical. Explain how this is possible, giving an example of the type of complex involved.
Optical isomerism can occur when a complex contains multidentate ligands arranged asymmetrically, forming non‑superimposable mirror images.
Examples: [M(en)3]n+ and[M(C2O42-)3]n+
Carbon monoxide (CO) is a highly poisonous gas. Using ideas of ligand strength, ligand exchange and stability of transition‑metal complexes, explain why CO is toxic when inhaled. Your answer should refer specifically to the Fe²⁺ centre in haemoglobin.
In normal conditions, O₂ acts as a ligand and reversibly binds to Fe²⁺ in haemoglobin.
When CO is inhaled, it competes with O₂ and undergoes ligand substitution, replacing O₂ at the iron centre:
Hb–Fe2+ − O2+CO→Hb–Fe2+− CO+O2
This exchange occurs because CO forms a far stronger coordinate bond to Fe²⁺ than O₂ does.
Because the Fe–CO complex is so stable, CO binds essentially irreversibly under physiological conditions.
Haemoglobin containing CO (carboxyhaemoglobin) cannot bind or release O₂, reducing oxygen delivery to tissues.
Even small amounts of CO shift the equilibrium strongly towards the Fe–CO complex, causing potentially fatal hypoxia.