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OCR A Jun 2012 Paper 5 Q5
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![Iron, copper and platinum are examples of transition elements. 10 (a) Define the term transition element. Show that iron fits this definition by use of full electron configurations of iron as the element and in its common oxidation states.[4] (b) Describe one precipitation reaction and one ligand substitution reaction of copper in the +2 oxidation state. Your answer should include reagents, relevant observations and balanced equations.[6]OCR 2012<br />
11 (c) Platinum is an extremely unreactive transition element. However, platinum does take part in a redox reaction with aqua regia, a mixture of concentrated hydrochloric and nitric acids. Two products of this reaction are hexachloroplatinic acid, H2PtCl 6, and nitrogen dioxide, NO2. (i) Use oxidation states to show that this is a redox reaction.[2] (ii) Write an equation for the reaction of platinum metal with aqua regia.[2] (d) Ammonium hexachloroplatinate, (NH4)2PtCl 6, is a complex of platinum used in platinum plating. Ammonium hexachloroplatinate contains the hexachloroplatinate ion. Draw a 3-D diagram to show the shape of a hexachloroplatinate ion. On your diagram, showthe charge on the ion the value of the bond angle. [3]OCR 2012 Turn over<br />
(e) Oxaliplatin is a neutral complex of platinum(II) used in cancer treatment. 12 A molecule of oxaliplatin has a square planar shape about the metal ion with two bidentate ligands. The structure of oxaliplatin is shown below. H2 N N H2 Pt (i) What is meant by a bidentate ligand ?[2] (ii) In the boxes below, show the structures of the two bidentate ligands in oxaliplatin. [2] [Total: 21]OCR 2012<br />
13 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE TURN OVER FOR QUESTION 6OCR 2012 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN12_question_5-0.jpg)
![Mark Scheme June 2012 Marks Guidance Answer (A transition element) has (at least) one ion with a partially filled d sub-shell/ d orbital (cid:57) Fe AND 1s22s22p63s23p63d64s2 (cid:57) Fe(II) / Fe2+ AND 1s22s22p63s23p63d6 (cid:57) Fe(III) / Fe3+ AND 1s22s22p63s23p63d5 (cid:57) 4s 2 ALLOW incomplete for partially filled DO NOT ALLOW d shell ALLOW 4s before 3d, i.e. 1s22s22p63s23p64s23d6 IF candidate has used subscripts OR caps OR [Ar], DO NOT ALLOW when first seen but credit subsequently, i.e. 1s22s22p63s23p63d6 1s22s22p63s23p64s23D6 [Ar]4s23d6 For Fe2+ and Fe3+, ALLOW 4s0 in electron configuration IGNORE electron configurations of elements other than Fe ANNOTATIONS MUST BE USED -------------------------------------------------------------------------------- ALLOW NaOH in equation if reagent not given in description ALLOW a small amount of NH3/ammonia DO NOT ALLOW concentrated NH3 DO NOT ALLOW just OH ALLOW Cu(OH)2(H2O)4 ALLOW any shade of blue ALLOW (s) as state symbol for ppt (may be in equation) ALLOW [Cu(H2O)6]2+ + 2OH (cid:111) Cu(OH)2(H2O)4 + 2H2O For NH3, also ALLOW: [Cu(H2O)6]2+ + 2NH3 (cid:111) Cu(OH)2(H2O)4 + 2NH4 ALLOW full equation, e.g. CuSO4 + 2NaOH (cid:111) Cu(OH)2 + Na2SO4 CuCl2 + 2NaOH (cid:111) Cu(OH)2 + 2NaCl F325 Question (a) (b) EXAMPLES MUST REFER TO Cu2+ FOR ALL MARKS PRECIPITATION Reagent NaOH(aq) OR KOH(aq) (cid:57) States not required Transition metal product AND observation Cu(OH)2 AND blue precipitate/solid (cid:57) Correct balanced equation Cu2+(aq) + 2OH(aq) (cid:127)(cid:111) Cu(OH)2(s) (cid:57) state symbols not required IF more than one example shown, mark example giving lower mark 17<br />
F325 Question (b) Mark Scheme June 2012 Marks Guidance 2 i.e. no brackets IF more than one example shown, mark example giving lower mark ALLOW NH3 in equation if reagent not given in description DO NOT ALLOW precipitate ALLOW royal blue, ultramarine blue or any blue colour that is clearly darker than for [Cu(H2O)6]2+ (cid:57) ----------------------------------------------- ALLOW CuCl4 ALLOW any shades of yellow, e.g. yellowgreen DO NOT ALLOW precipitate ALLOW other correct ligand substitutions using same principles for marking as in two examples given ALLOW 1 mark for Pt from 0 to +4 AND N from +5 to +4 i.e. oxidation and reduction not identified or wrong way round DO NOT ALLOW Pt is oxidised and N reduced with no evidence DO NOT ALLOW responses using other incorrect oxidation numbers (CON) 18 Answer LIGAND SUBSTITUTION2 likely Reagent NH3(aq)/ammonia (cid:57) State not required Transition metal product AND observation [Cu(NH3)4(H2O)2]2+ AND deeper/darker blue (solution) (cid:57) Correct balanced equation [Cu(H2O)6]2+ + 4NH3 (cid:127)(cid:111) [Cu(NH3)4(H2O)2]2+ + 4H2O (cid:57) OR ------------------------------------------------------- Reagent Concentrated HCl State not required Transition metal product AND o CuCl ]2 AND yellow (solution) (cid:57) [ Correct balanced equation Cu(H O) ]2+ + 4Cl (cid:127)(cid:111) [CuCl ]2 + 6H O (cid:57) [ OR (dilute) HCl(aq) OR NaCl(aq) (cid:57) bservation (i) Pt oxidised from 0 +4 (cid:57) N reduced from +5 to +4 (cid:57) (c)<br />
F325 Mark Scheme June 2012 Question Answer (c) (ii) Pt + 6HCl + 4HNO3 (cid:127)(cid:111) H2PtCl6 + 4NO2 + 4H2O (cid:57)(cid:57) Marks Guidance (d) Cl Cl Cl Pt Cl Cl Cl OR 3-D Shape 1 mark Correct 3-D diagram of Pt surrounded by 6Cl ONLY (cid:57) Bond angle Charge 1 mark bond angle of 90 on diagram or stated (cid:57) 1 mark 2 charge shown outside of brackets (cid:57) + H2O 1st mark for ALL species correct and no extras: i.e: Pt + HCl + HNO3 (cid:127)(cid:111) H2PtCl6 + NO2 DO NOT ALLOW charge on Pt, e.g. Pt2+ 2nd mark for correct balancing ALLOW correct multiples Must contain 2 out wedges, 2 in wedges and 2 lines in plane of paper OR 4 lines, 1 out wedge and 1 in wedge For bond into paper, ALLOW: IGNORE charges on Pt and Cl for this mark The 2 marks for charge AND bond angle are ONLY available from a diagram showing Pt bonded to 6 Cl ONLY ALLOW ONLY if diagram has Pt surrounded by 6Cl ONLY BUT 3-D shape may not be correct DO NOT ALLOW if ANY charges shown on Pt or Cl within brackets 19<br />
F325 Mark Scheme June 2012 Question Answer (e) (i) Donates two electron pairs to a metal (ion) (cid:57) forms two coordinate bonds (cid:57) (ii) NH2 NH2 (cid:57) (cid:57) Marks Guidance ALLOW lone pairs for electron pairs ALLOW dative (covalent) bond for coordinate bond ALLOW 1 mark for a full definition of a ligand (without reference to 2: i.e. Donates an electron pair to a metal (ion) forming a coordinate bond (cid:57) ALLOW displayed formulaecharges essential in (COO)2 structure DO NOT ALLOW H2N Total 21 20<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_5_QP_JUN12_answer_5-0.jpg)
