A-LevelChemistryChemical bonding9701/43 · Oct/Nov 2021 · Q514 Marks

(a) [MnCl4]2- is a complex ion.

(a)(i)Deduce the oxidation state of manganese in [MnCl4]2-.[1]
(a)(ii)The [MnCl4]2- complex does not contain any 180° bond angles. Draw a three-dimensional diagram to show the shape of the [MnCl4]2- complex. State one bond angle on your diagram.[2]
(b)(i)[Co(H2O)6]²+ and an excess of NaOH(aq) equation observation[2]
(b)(ii)[Co(H2O)6]2+ and an excess of NH3(aq) equation observation[2]
(b)(iii)[Co(H2O)6]2+ and an excess of NaCl(aq) equation observation[2]
(b)(iv)Name the type of reaction that occurs in (b)(iii).[1]
(c)(i)Define the term bidentate ligand.[2]
(c)(ii)Draw three-dimensional diagrams for the two optical isomers of [Co(NH3)2(en)2]2+. Each en ligand can be represented using N N[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] +2
[1] correct 3D tetrahedral structure with Mn at center, Cl at corners, overall charge 2-
[1] bond angle labelled 109.5°
[1] [Co(H2O)6]2+ + 2OH- → Co(H2O)4(OH)2 + 2H2O OR [Co(H2O)6]2+ + 2OH- → Co(OH)2 + 6H2O
[1] blue precipitate
[1] [Co(H2O)6]2+ + 6NH3 → [Co(NH3)6]2+ + 6H2O
[1] yellow / brown / straw solution
[1] [Co(H2O)6]2+ + 4Cl- → [CoC4]2- + 6H2O
[1] blue solution
[1] ligand exchange
[1] (a species) that donates two lone pairs to form two dative bonds
[1] to a (transition) metal atom / metal ion
[1] M1 one correct 3D structure - trans or cis
[1] M2 a correct optical isomer of M1 [must 3D]

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