Transition Metals and their ChemistryEdexcel International A Level Chemistry: Topic test

20 questions, 54 marks

Edexcel International A Level Chemistry

Transition Metals and their Chemistry topic test

Total 54 marks

Name

Class

Date

1
Cobalt (atomic number 27) is a Period 4 d-block element. It forms stable ions with charges of 2+ and 3+ in its compounds.
(a)
What is the electronic configuration of a Co³⁺ ion?
[1 mark]
A[Ar] 3d⁷
B[Ar] 3d⁶
C[Ar] 3d⁴ 4s²
D[Ar] 3d⁶ 4s¹
(b)
Which statement best explains why cobalt forms ions with more than one oxidation number?
[1 mark]
A3d electrons are held more strongly than 4s electrons, so they are lost first
BCobalt has several naturally occurring isotopes
CCobalt atoms have no electrons in the 4s sub-shell
DThe 3d and 4s sub-shells are close in energy, so different numbers of electrons can be lost using similar energy
(c)
Write the full electronic configuration of a Co²⁺ ion using sub-shell notation, and use it to explain why cobalt is classified as a transition metal.
[2 marks]
Total for question 1: 4 marks
2
Chromium(III) forms the octahedral complex ion [Cr(H₂O)₆]³⁺ in aqueous solution. In a second complex ion, three molecules of 1,2-diaminoethane, H₂NCH₂CH₂NH₂ (en), act as ligands to the chromium(III) ion.
(a)
What is the coordination number of chromium in [Cr(en)₃]³⁺?
[1 mark]
A6
B3
C9
D4
(b)
Which description of the bond between a 1,2-diaminoethane ligand and the Cr³⁺ ion is correct?
[1 mark]
AIonic attraction between oppositely charged ions
BA covalent bond in which each atom donates one electron
CA dative covalent bond in which a nitrogen lone pair is donated to the Cr³⁺ ion
DA hydrogen bond between an N–H group and the chromium ion
(c)
Explain why 1,2-diaminoethane is described as a bidentate ligand, and state the shape of the [Cr(en)₃]³⁺ ion.
[2 marks]
Total for question 2: 4 marks
3
A solution containing Ti³⁺(aq) ions is purple, whereas a solution containing Ti⁴⁺(aq) ions is colourless. Titanium has atomic number 22.
(a)
Explain, in terms of d-orbitals and d electrons, why the Ti³⁺(aq) solution is coloured but the Ti⁴⁺(aq) solution is colourless.
[3 marks]
(b)
(i) Write the electronic configuration of a Ti atom using sub-shell notation. [1]
(ii) Explain why replacing the water ligands in [Ti(H₂O)₆]³⁺ with chloride ions would be expected to change the colour of the solution. [2]
(iii) State one other change, apart from a change of ligand, that can cause a colour change in a transition metal complex. [1]
[4 marks]
Total for question 3: 7 marks
4
A chemist works with aqueous chromium(III) ions, present as the octahedral complex ion [Cr(H₂O)₆]³⁺. In one experiment she oxidises these ions to chromium(VI). In a separate experiment she adds EDTA⁴⁻, a hexadentate ligand, and the following reaction occurs: [Cr(H₂O)₆]³⁺ + EDTA⁴⁻ → [Cr(EDTA)]⁻ + 6H₂O
(a)
Describe how the chemist could convert the aqueous chromium(III) ions into orange dichromate(VI) ions, Cr₂O₇²⁻. Give the reagents, the colour change at each stage and an equation for the oxidation step.
[6 marks]
(b)
Explain why the substitution of six water ligands by one EDTA⁴⁻ ion gives a more stable complex ion, even though the coordination number does not change, and explain why the colour of the solution would be expected to change when the ligands change.
[6 marks]
Total for question 4: 12 marks
5
An unlabelled solution contains a single transition metal(II) ion. When aqueous sodium hydroxide is added dropwise, a pale green precipitate forms. On standing in air, the surface of the precipitate slowly turns orange-brown. The precipitate does not dissolve in excess sodium hydroxide.
(a)
Which metal(II) ion is present in the solution?
[1 mark]
ANi²⁺
BCu²⁺
CFe²⁺
DMn²⁺
(b)
Which ionic equation represents the formation of the pale green precipitate?
[1 mark]
AFe²⁺(aq) + 2OH⁻(aq) → Fe(OH)₂(s)
BFe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)
C[Fe(H₂O)₆]²⁺(aq) + 6OH⁻(aq) → [Fe(OH)₆]⁴⁻(aq) + 6H₂O(l)
DFe²⁺(aq) + OH⁻(aq) → FeOH⁺(aq)
(c)
Explain, in terms of oxidation number, what happens to the precipitate on standing in air, and write a balanced equation for the reaction.
[2 marks]
Total for question 5: 4 marks
6
In the Haber process, nitrogen and hydrogen react at about 450 °C and 200 atm over a solid iron catalyst: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
(a)
Why is the iron catalyst described as a heterogeneous catalyst?
[1 mark]
AIt is a transition metal
BIt forms an intermediate species with the reactants in solution
CIt is in the same phase as the reactants
DIt is in a different phase from the reactants, and the reaction occurs at its surface
(b)
Which statement describes a step in heterogeneous catalysis on a metal surface?
[1 mark]
AReactants desorb from the surface before they react
BAdsorption of reactant molecules weakens their bonds, and the products later desorb
CThe catalyst is used up in the first step and reformed as a different compound
DThe products adsorb strongly and stay on the surface
(c)
The iron catalyst is used as small pellets with a very large surface area. Explain why a large surface area is an advantage, and why a metal that adsorbs the gases extremely strongly would be a poor catalyst.
[2 marks]
Total for question 6: 4 marks
7
A water-treatment chemist determines the concentration of copper(II) ions in a sample of waste water using EDTA⁴⁻, a hexadentate ligand. The reaction is Cu²⁺ + EDTA⁴⁻ → [Cu(EDTA)]²⁻. A 25.0 cm³ sample of the waste water reacted exactly with 18.40 cm³ of 0.0200 mol dm⁻³ EDTA⁴⁻. Ar of Cu = 63.5.
(a)
Calculate the concentration of copper(II) ions in the waste water in mol dm⁻³.
[3 marks]
(b)
(i) Calculate the mass of copper in each dm³ of the waste water. [2]
(ii) State the coordination number of copper in [Cu(EDTA)]²⁻ and explain how a single EDTA⁴⁻ ion achieves this. [2]
[4 marks]
Total for question 7: 7 marks
8
Iron (atomic number 26) forms the aqueous ions [Fe(H₂O)₆]²⁺, which is pale green, and [Fe(H₂O)₆]³⁺, which is yellow-brown. A student also investigates their reactions with aqueous bases.
(a)
Explain why iron is classified as a transition metal, and why its two aqueous ions are coloured but have different colours. Include the electronic configurations of Fe, Fe²⁺ and Fe³⁺.
[6 marks]
(b)
Describe what is observed when aqueous sodium hydroxide is added dropwise and then in excess to aqueous iron(III) ions, and when aqueous ammonia is added in the same way. Write an ionic equation for each reaction and explain the role of each reagent.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).