CIE A Level Chemistry
CIE A Level Chemistry Chemistry of Transition Elements Exam Questions
Free CIE A Level Chemistry exam questions for Chemistry of Transition Elements, with a mark scheme for every pack. Covers transition element properties, oxidation states, complex ions, ligands, shapes, isomerism, colour, ligand exchange, stability constants and redox titrations.
Chemistry of Transition Elements 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 CIE A Level Chemistry Chemistry of Transition Elements
The chemistry of transition elements is an A Level topic in Cambridge International 9701, covering the d-block elements titanium to copper. You need to define a transition element, explain variable oxidation states and catalytic behaviour, and describe complex ions, ligands, coordination numbers and geometries including octahedral, tetrahedral and square planar. The topic includes stereoisomerism in complexes, the splitting of d orbitals, explanations of colour, ligand exchange with stability constants, and redox titrations using manganate(VII) and dichromate(VI). It links to electrochemistry, equilibria and atomic structure. It is tested in Paper 4, and examiners regularly ask for configurations of ions, observations in ligand exchange and titration calculations.
What you need to know
- Definition A transition element is a d-block element that forms one or more stable ions with incomplete d orbitals. Scandium and zinc are not transition elements because Sc3+ is d0 and Zn2+ is d10.
- General properties Variable oxidation states, formation of complex ions, coloured compounds and catalytic activity. Similar energies of the 3d and 4s electrons allow different numbers of electrons to be lost.
- Complexes and ligands A ligand donates a lone pair to the central metal ion forming a coordinate bond. Ligands can be monodentate (H2O, NH3, Cl-), bidentate (ethane-1,2-diamine, ethanedioate) or polydentate (EDTA4-).
- Shapes and isomerism Six-coordinate complexes are octahedral, [CuCl4]2- is tetrahedral, cisplatin is square planar and [Ag(NH3)2]+ is linear. Complexes can show cis-trans and optical isomerism, for example [Ni(en)3]2+.
- Colour Ligands split the d orbitals into two sets of different energy. Light of a particular frequency is absorbed when an electron is promoted, and the complementary colour is seen. Changing the ligand changes delta E and therefore the colour.
- Ligand exchange [Cu(H2O)6]2+ (blue) forms pale blue Cu(OH)2 with a little NH3, then deep blue [Cu(NH3)4(H2O)2]2+ with excess. Adding concentrated HCl gives yellow [CuCl4]2-. Stability constant Kstab measures how favourable the new complex is.
- Redox titrations MnO4- + 8H+ + 5Fe2+ → Mn2+ + 5Fe3+ + 4H2O, self-indicating from colourless to pale pink. Acidified dichromate(VI) and the iodine/thiosulfate system are also used.
Common mistakes in Chemistry of Transition Elements
- Removing 3d electrons before 4s when forming ions; 4s electrons are always lost first.
- Saying the colour seen is the colour absorbed; you see the complementary colour that is transmitted.
- Giving the coordination number as the number of ligands; it is the number of coordinate bonds, so three bidentate ligands give six.
- Forgetting the 1:5 mole ratio of MnO4- to Fe2+ in titration calculations.
- Saying zinc is a transition element because it is in the d-block; Zn2+ has a full 3d10 subshell.
Try three Chemistry of Transition Elements exam-style questions
1. 25.0 cm3 of an iron(II) solution reacted with 22.50 cm3 of 0.0200 mol dm-3 acidified potassium manganate(VII). Calculate the concentration of Fe2+. (3 marks)
Show the mark scheme answer
Moles MnO4- = 0.0200 x 0.02250 = 4.50 x 10^-4; moles Fe2+ = 5 x 4.50 x 10^-4 = 2.25 x 10^-3; concentration = 2.25 x 10^-3/0.0250 = 0.0900 mol dm-3.
2. Explain why transition metal complexes are coloured. (3 marks)
Show the mark scheme answer
Ligands cause the d orbitals to split into two energy levels; electrons absorb light of a certain frequency to move to the higher level; the remaining (complementary) colour is transmitted and seen.
3. Describe what is observed when aqueous ammonia is added dropwise until in excess to aqueous copper(II) sulfate. (3 marks)
Show the mark scheme answer
Pale blue precipitate of Cu(OH)2 forms; which dissolves in excess ammonia; to give a deep blue solution of [Cu(NH3)4(H2O)2]2+.
Chemistry of Transition Elements FAQs
What does Cambridge A Level Chemistry Chemistry of transition elements cover?
It covers properties of transition elements, complex ions, ligands, shapes, isomerism, colour from d orbital splitting, ligand exchange and stability constants, and redox titrations.
Which paper tests transition elements in 9701?
It is A Level content, so it is tested in Paper 4, with practical aspects such as titrations also appearing in the practical papers.
What observations should I learn for transition elements?
Learn the colours of the common aqua complexes, the precipitates with NaOH and NH3, and the colour changes in ligand exchange for copper and cobalt.
