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OCR A Jun 2015 Paper 5 Q1
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![Answer all the questions. This question looks at properties of transition elements, ions and complexes. (a) What is the oxidation number of Cr in the complex ion [CrOCl5]2?[1] (b) Write the equation for a reaction catalysed by a named transition element, compound or ion. Equation:Catalyst:[1] (c) An octahedral complex ion A, C9H30N6Ni3+, exists as two optical isomers. In complex ion A, Ni3+ is bonded to three molecules of a bidentate ligand B. (i) State what is meant by a bidentate ligand.[1] (ii) What is the molecular formula of the bidentate ligand B?[1] (iii) Draw a possible structure for B and explain how B is able to act as a bidentate ligand.[2] (iv) What is the coordination number of complex ion A?[1]OCR 2015<br />
(v) Complete the 3-D diagrams of the shapes of the optical isomers of complex ion A. You can show the bidentate ligand simply as 3+ 3+ Ni Ni [1] (d) Describe the reactions of EITHER aqueous copper(II) ions OR aqueous cobalt(II) ions with: aqueous sodium hydroxide excess aqueous ammonia hydrochloric acid.In your answer you should link observations with equations.[6]OCR 2015 [Total: 14] Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN15_question_1-0.jpg)
![F325 Question 1 1 (a) (b) (+)5 (cid:57) For equations, IGNORE any state symbols; ALLOW multiplesAny correct equation for a reaction catalysed by a transition element, compound or ion AND transition element, compound or ion (by formula or name) (cid:57) (c) (c) (c) (i) Donates two electron pairs (to a metal ion) AND forms two coordinate bonds (to a metal ion) (cid:57) NOTE: Metal ion not required as Ni3+ is in the question (ii) C3H10N2 (cid:57) (iii) MARK INDEPENDENTLYH2NCH2CH2CH2NH2 (cid:57) Each N OR each NH2 OR amine group has a lone pair/electron pair OR lone pairs shown on N atoms in structure (cid:57) Mark Scheme June 2015 Answer Marks Guidance 1 1 ALLOW 5+ OR V OR Cr5+ EXAMPLES N2 + 3H2 (cid:1185) 2NH3 (allow (cid:314)) AND Fe/iron oxide 2SO2 + O2 (cid:1185) 2SO3 (allow (cid:314)) AND V2O5/Pt 2CO + 2NO2CO2 + N2 AND Pt/Pd/Rh/Au Equation for any alkene + H2alkane AND Ni/Pt/Pd C6H6 + Cl2C6H5Cl + HCl AND Fe/FeCl3/Fe3+ C6H6 + Br2C6H5Br + HBr AND Fe/FeBr3/Fe3+ 2H2O22H2O + O2 AND MnO2 For other examples, CHECK with TL ALLOW lone pairs for electron pairs ALLOW dative (covalent) bonds for coordinate bonds TWO is only needed once, e.g. Donates two electron pairs to form coordinate bonds Donates electron pairs to form two coordinate bonds ALLOW in any order IGNORE structure ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) ALLOW H2NCH2CH(CH3)NH2 OR H2NCH(CH2CH3)NH2 ALLOW secondary or tertiary diamines or mixture IGNORE complex ion For other examples, CHECK with TL<br />
F325 Question 1 (c) Answer (iv) 6 (cid:57) (c) (v) 3D diagrams of BOTH optical isomers required for the mark Mark Scheme June 2015 Marks Guidance In this part, Charge AND Square brackets NOT required IGNORE N or attempts to draw structure of bidentate ligand Other orientations possible but all follow same principle with 2nd structure being a mirror image of the first Ni Ni AND (cid:57)<br />
F325 Question 1 (d) (d) (d) Mark Scheme June 2015 Answer Marks Guidance Quality of written communication Observation must be linked to the correct reaction REACTIONS OF AQUEOUS Cu2+REACTION OF Cu2+ with NaOH(aq) Correct balanced equation Cu2+(aq) + 2OH(aq)Cu(OH)2(s) (cid:57) state symbols not required Observation blue precipitate/solid (cid:57) REACTION OF Cu2+ WITH excess NH3(aq) Correct balanced equation [Cu(H2O)6]2+ + 4NH3[Cu(NH3)4(H2O)2]2+ + 4H2O (cid:57) Observation deep/dark blue (solution) (cid:57) REACTION OF Cu2+ WITH HCl(aq) Correct balanced equation [Cu(H2O)6]2+ + 4Cl[CuCl4]2 + 6H2O (cid:57) Observation yellow (solution) (cid:57) FULL ANNOTATIONS MUST BE USED THROUGHOUT ALLOW some reactions for Cu2+ and some for Co2+ ALLOW equilibrium signs in all equations IGNORE any incorrect initial colours IGNORE state symbols IGNORE an incorrect formula for an observationALLOW [Cu(H2O)6]2+ + 2OHCu(OH)2(H2O)4 + 2H2O ALLOW full or hybrid equations, e.g. Cu2+ + 2NaOHCu(OH)2 + 2Na+ [Cu(H2O)6]2+ + 2OHCu(OH)2 + 6H2O 4 + 2NaOHCu(OH)2 + Na2SO4 ALLOW any shade of blue CuSO IGNORE initial precipitation of Cu(OH)2 IGNORE [Cu(NH3)4]2+ ALLOW royal blue, ultramarine blue or any blue colour that is clearly darker than for [Cu(H2O)6]2+ DO NOT ALLOW deep blue precipitate for observation IGNORE mention of different concentrations of HCl ALLOW CuCl4 ALLOW [Cu(H2O)6]2+ + 4HCl[CuCl4]2 + 6H2O + 4H+ IGNORE Cu2+ + 4ClCuCl4 2 ALLOW greenyellow OR yellowgreen DO NOT ALLOW yellow precipitate for observation 2 i.e. no brackets OR Cu(Cl)4 2<br />
F325 Question 1 (d) (d) (d) Mark Scheme June 2015 Answer Marks Guidance Quality of written communication Observation must be linked to the correct reaction REACTIONS OF AQUEOUS Co2+REACTION OF Co2+ with NaOH(aq) Correct balanced equation Co2+(aq) + 2OH(aq)Co(OH)2(s) (cid:57) state symbols not required Observation blue precipitate/solid (cid:57) REACTION OF Co2+ WITH excess NH3(aq) Correct balanced equation [Co(H2O)6]2+ + 6NH3[Co(NH3)6]2+ + 6H2O (cid:57) Observation brown/yellow (solution) (cid:57) REACTION OF Co2+ WITH HCl(aq) Correct balanced equation [Co(H2O)6]2+ + 4Cl[CoCl4]2 + 6H2O (cid:57) Observation blue (solution) (cid:57) FULL ANNOTATIONS MUST BE USED THROUGHOUT ALLOW some reactions for Cu2+ and some for Co2+ ALLOW equilibrium signs in all equations IGNORE any incorrect initial colours IGNORE state symbols IGNORE an incorrect formula for an observationALLOW [Co(H2O)6]2+ + 2OHCo(OH)2(H2O)4 + 2H2O ALLOW full or hybrid equations, e.g. Co2+ + 2NaOHCo(OH)2 + 2Na+ [Co(H2O)6]2+ + 2OHCo(OH)2 + 6H2O 4 + 2NaOHCo(OH)2 + Na2SO4 ALLOW any shade of blue CoSO IGNORE changes in colour over time IGNORE initial precipitation of Co(OH)2 ALLOW any shade of brown or yellow DO NOT ALLOW brown/yellow precipitate for observation IGNORE mention of different concentrations of HCl ALLOW CoCl4 ALLOW [Co(H2O)6]2+ + 4HCl[CoCl4]2 + 6H2O + 4H+ IGNORE Co2+ + 4ClCoCl4 2 ALLOW any shades of blue DO NOT ALLOW blue precipitate for observation 2 i.e. no brackets OR Co(Cl)4 2 Total 14<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN15_answer_1-0.jpg)
