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OCR A Jun 2016 Paper 5 Q1
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![Answer all the questions. This question is about the chemistry of copper compounds and complex ions. (a) The flowchart shows two reactions of aqueous copper(II) sulfate. In the boxes, write the formulae and colours of the complex ions formed. CuSO4(aq) NH3(aq) HCl(aq) complex ion:complex ion:colour:colour:(b) Cu2+ ions form a complex ion A with two ethanedioate ions and two water molecules. The ethanedioate ion is a bidentate ligand. The skeletal formula of the ethanedioate ion is shown in Fig. 1.1 below. [3] O O Fig. 1.1 (i) What is meant by the term bidentate ligand ?[1]OCR 2016<br />
(ii) The complex ion A exists as three stereoisomers. The shape of one of the stereoisomers is shown below. The charge has been omitted. H2O Cu H2O Complex A Complete the 3D diagrams of the other two stereoisomers of A. You do not need to include any charges. Indicate with ticks whether the stereoisomers are cis, trans, optical or a combination of these types. Stereoisomer Cu Cu Type cis trans optical cis trans optical (iii) What is the empirical formula, including the charge, of the complex ion A?[2] [3]OCR 2016 [Total: 9] Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN16_question_1-0.jpg)
![Mark scheme Marks F325 Question 1 (a) Answer IGNORE any charges shown within complexes (treat as rough working) Formulae 2 marks [Cu(NH3)4(H2O)2]2+ (cid:57) [CuCl4]2 (cid:57) Colours blue AND yellow (cid:57) Mark independently of formulae 1 mark (b) (i) Donates two electron pairs to a metal ion/metal/Cu2+ AND forms two coordinate bonds to a metal ion/metal/Cu2+ (cid:57) June 2016 Guidance For charges, ALLOW +2 and 2 Square brackets required, i.e. DO NOT ALLOW Cu(NH3)4(H2O)2 ALLOW Ligands in any order ALLOW CuCl4 For CuCl4 2+ 2 i.e. no brackets OR Cu(Cl)4 2 2, ALLOW greenyellow OR yellowgreen DO NOT ALLOW green For [Cu(NH3)4(H2O)2]2+ DO NOT ALLOW pale blue, light blue DO NOT ALLOW precipitate with blue OR yellow ALLOW lone pairs for electron pairs ALLOW molecule/atom/ion/substance for ligand ALLOW dative (covalent) bonds for coordinate bonds ALLOW transition element for metal Two is needed once only e.g. Donates two electron pairs to form coordinate bonds to a metal ion/metal/Cu2+ Donates electron pairs to form two coordinate bonds to a metal ion/metal/Cu2+ DO NOT ALLOW donates two electron pairs to form one/a coordinate bond<br />
F325 Question 1 (b) (ii) Answer Mark scheme Marks cis (cid:57) trans optical (cid:57) cis trans (cid:57) optical June 2016 Guidance FULL ANNOTATIONS MUST BE USED -------------------------------------------------------------------------------- 2 marks: one for each correct isomer (cid:57)(cid:57) TAKE CARE: structures may be in different orientations and in different order IF BOTH isomers are correct, but O connectivity wrong, AWARD 1 mark for both structures Check H2O ligands carefully for connectivity ALLOW H2O reversed shown as O2H IGNORE charges (anywhere) ------------------------------------------------------------------- NOTE: For each structure, ALL O atoms must be shown AND For (COO)2, ALLOW skeletal, structural or displayed formula DO NOT ALLOW structures such as those shown below 1 mark: for whole of 2nd row for whole of Type row i.e. (cis AND optical) AND trans only<br />
F325 Question 1 (b) (iii) Answer 2 CuC4H4O10 Formula (cid:57) 2 charge (cid:57) MARK formula and charge INDEPENDENTLY Mark scheme Marks June 2016 Guidance Empirical formula essential, e.g. DO NOT ALLOW Cu(COO)2(H2O)2 for formula mark ALLOW any order of elements in formula ALLOW 2 for charge Total<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN16_answer_1-0.jpg)
