Edexcel A Level Chemistry
Edexcel A Level Chemistry Topic 15: Transition Metals Exam Questions
Free Edexcel A Level Chemistry exam questions for Topic 15: Transition Metals, with a mark scheme for every pack. Covers transition metal configurations, complex ions, ligands, shapes, colour, oxidation states, ligand exchange, catalysis and reactions of common ions.
Topic 15: Transition Metals exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel A Level Chemistry Topic 15: Transition Metals
Topic 15 of Edexcel A Level Chemistry covers the d-block transition metals. You define a transition metal, write configurations of atoms and ions, and describe complex ions with monodentate, bidentate and multidentate ligands, their shapes (octahedral, tetrahedral, square planar and linear) and isomerism, including cisplatin. Colour is explained by d orbital splitting. The topic includes variable oxidation states, the chemistry of vanadium, chromium, manganese, iron, cobalt, copper and zinc compounds, ligand exchange and the chelate effect, and heterogeneous and homogeneous catalysis. It is assessed in Paper 1. Examiners regularly ask for observations with NaOH and ammonia, explanations of colour and equations for ligand exchange.
What you need to know
- Definition and configurations A transition metal is an element that forms one or more stable ions with an incompletely filled d subshell. Scandium and zinc are d-block elements but not transition metals, and 4s electrons are lost first.
- Complexes and ligands Ligands donate lone pairs to the metal ion through dative covalent bonds. Examples: H2O and NH3 (monodentate), ethane-1,2-diamine (bidentate) and EDTA4- (hexadentate).
- Shapes and isomerism Six-coordinate complexes are octahedral, [CuCl4]2- is tetrahedral, cisplatin is square planar and [Ag(NH3)2]+ is linear. Cisplatin acts as an anticancer drug by binding to DNA.
- Colour Ligands split d orbitals into two energy levels. Electrons absorb visible light to be promoted, and the complementary colour is transmitted. Colour depends on the metal, oxidation state, ligand and coordination number.
- Reactions with OH- and NH3 Cu2+ gives a blue precipitate that dissolves in excess NH3 to form a deep blue solution; Fe2+ gives a green precipitate, Fe3+ an orange-brown precipitate, and Cr3+ a grey-green precipitate that is amphoteric.
- Ligand exchange and the chelate effect Replacing monodentate ligands with multidentate ones increases the number of particles, so entropy increases and the complex is more stable.
- Catalysis Heterogeneous catalysts adsorb reactants on their surface (V2O5 in the Contact process). Homogeneous catalysts work through variable oxidation states, such as Fe2+ in the reaction of iodide with peroxodisulfate.
Common mistakes in Topic 15: Transition Metals
- Writing Fe3+ as [Ar]3d3 4s2; it is [Ar]3d5.
- Describing the colour seen as the colour absorbed.
- Saying the chelate effect is due to stronger bonds; the main reason is the increase in entropy.
- Forgetting that [CuCl4]2- is tetrahedral because chloride ions are large.
- Writing ligand exchange equations with unbalanced charges.
Try three Topic 15: Transition Metals exam-style questions
1. Explain why [Cu(H2O)6]2+ is coloured but [Zn(H2O)6]2+ is not. (3 marks)
Show the mark scheme answer
Cu2+ has an incomplete 3d subshell (3d9); d orbitals split by ligands and electrons absorb visible light to move to the higher level, transmitting the complementary colour; Zn2+ is 3d10 so no d-d transition is possible.
2. Write an equation for the reaction of [Cu(H2O)6]2+ with excess concentrated hydrochloric acid and state the colour change. (2 marks)
Show the mark scheme answer
[Cu(H2O)6]2+ + 4Cl- → [CuCl4]2- + 6H2O; blue to yellow (green intermediate).
3. Explain why the reaction [Cu(H2O)6]2+ + 3en → [Cu(en)3]2+ + 6H2O is favourable. (2 marks)
Show the mark scheme answer
Four particles become seven particles; entropy increases (delta S positive), so delta G is negative (chelate effect).
Topic 15: Transition Metals FAQs
What does Edexcel A Level Chemistry Topic 15 Transition Metals cover?
It covers configurations, complex ions, ligands, shapes, colour, oxidation states, reactions with hydroxide and ammonia, ligand exchange and catalysis.
Which paper is Transition Metals examined in?
Topic 15 is assessed in Paper 1, Advanced Inorganic and Physical Chemistry, and in Paper 3.
What observations should I learn for transition metals?
Learn the colours of the hexaaqua ions and the precipitates with NaOH and ammonia for Cr3+, Fe2+, Fe3+, Co2+ and Cu2+, and whether they dissolve in excess.
