Edexcel Jan 2014 (IAL) Paper 5 Q22 (with explained solutions) |

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Edexcel Jan 2014 (IAL) Paper 5 Q22

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22 The scheme below summarises some reactions of copper and its compounds. Cu Cl2(g) conc. HCl(aq) brown solid yellow solution H2O(l) reagent X CuI(s) brown solution F reagent Y Cu2+(aq) tartrate ions in alkali red-brown solid ethanal warm copper(II) complex pale blue precipitate reagent X dark blue solution (a) (i) Identify the copper containing species A to E either by name, including the oxidation number, or by formula. Also, identify the brown solution, F. (6) ABCDEF(ii) Identify the reagents X and Y. (2) XY*P42993A01328* 13 Turn over<br />
(iii) Identify the organic product of the reaction between the copper(II) complex and ethanal. Hence explain the role of ethanal in the reaction. (2)(iv) The reaction between Cu2+(aq) and reagent Y forms CuI(s) and a brown solution, F. This reaction is the first stage in a method for the determination of the concentration of Cu2+(aq). Outline briefly how this method is used. Practical details are not required. (1)*(b) (i) Explain why B is coloured. (4)(ii) Explain why B and D have different colours. (2)14 *P42993A01428*<br />
(c) Aqueous copper(I) ions undergo a disproportionation reaction. (i) Write the ionic equation for this reaction. Include state symbols in your answer. (ii) Explain, stating the relevant oxidation numbers, why the reaction in (c)(i) is classified as a disproportionation. (1) (1)(iii) Use the standard reduction potentials on page 17 of the Data Booklet to cell for this disproportionation. Hence show that this reaction is calculate E (cid:57) thermodynamically feasible. (2) (Total for Question 22 = 21 marks) *P42993A01528* 15 Turn over<br />

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Acceptable Answers Question Number 22(a)(i) If name and formula are given, both must 2(1) be correct A = copper(II) chloride / CuCl2 (1) B = tetrachlorocuprate(II) (ion) / CuCl4 ALLOW B = trichlorocuprate(II) / CuCl3 C = copper(II) hydroxide / Cu(OH)2 / Cu(OH)2(H2O)4 (1) D = tetraamminecopper(II) (ion) / Cu(NH3)4 E = copper(I) oxide / Cu2O (1)/ KI3 F = iodine / I2 / triiodide (ion) / I3 (1) IGNORE state symbols even if incorrect. correct oxidation numbers with formula. order of the ligands. 2+ / Cu(H2O)2(NH3)4 2+ (1) Question Number 22(a)(ii) If name and formula are given, both Acceptable Answers must be correct X = (aqueous) ammonia / NH3(aq) ALLOW NH3 / ammonium hydroxide (1) Y = potassium iodide / KI ALLOW other soluble iodides (1) IGNORE references to concentration Reject Mark B = CuCl2 Reject Mark X = NaOH iodide / I KI and acid HI<br />
Acceptable Answers Question Number 22(a)(iii) (Product is) ethanoic acid / CH3COOH / ethanoate( ions) / CH3COO (1) IGNORE carboxylic Ethanal is a reducing agent / reduces Cu2+ (1) Stand alone marks IGNORE references to oxidation of ethanol products of reduction (e.g. Cu) Question Number 22(a)(iv) (Iodine is formed quantitatively and is Acceptable Answers determined by) titration against sodium thiosulfate solution (of known concentration) Question Number 22(b)(i) (3)d orbitals / (3)d subshell split (by the Acceptable Answers attached ligands) (1) Electrons are promoted (from lower to higher energy d orbital(s) / levels) OR Electrons move from lower to higher energy d orbital(s) / levels) ALLOW dd transitions occur (1) Absorbing energy /photons of a certain frequency (in the visible region) ALLOW Absorbing light (1) Reflected / transmitted / remaining light is coloured / yellow / in the visible region ALLOW Complementary colour seen Reflected / transmitted / remaining light / frequency is seen (1) Penalise omission of (3)d once only. Ignore reference to electrons relaxing / dropping to the ground state Reject Mark Reject Mark Colorimetry Reject Mark Orbital / shell is split<br />
Acceptable Answers Question Number 22(b)(ii) Colour depends on the frequency Reject Mark /wavelength /energy of the absorbed light (1) Different ligands split the d orbitals to a different extent (1) Question Number 22(c)(i) 2Cu+(aq)Cu(s) + Cu2+(aq) Acceptable Answers Reject Electrons Reject ALLOW reversible arrows Question Number 22(c)(ii) The copper(I) is oxidized to Acceptable Answers copper(II) and (in the same reaction) reduced to copper((0)) OR Copper changes from +1 to 0 and +2 IGNORE Reference to a Cu atom Question Number 22(c)(iii) Relevant reduction potentials are Acceptable Answers Reject Mark Cu2+ + eCu+ Eo = +0.15 (V) Cu+ + eCu Eo = +0.52 (V) ALLOW single arrows (1) Eo TE on incorrect Eo values providing Eo positive (Eo thermodynamically favourable) cell = 0.520.15 = (+)0.37 (V) (1) cell positive so reaction cell is Total for Question 22 = 21 marks Mark Mark<br />
Acceptable Answers Reject Mark Question Number 23(a) Elem ent C mol Ratio 40.44 12 = 3.37 7.871 = 7.87 35.9616 = 2.2475 2.00 15.7314 = 1.12357 (1) (1) Empirical formula = C3H7O2N (1) Symbols in any order Stand alone mark No TE on incorrect ratio IGNORE significant figure and rounding errors except 1sf in mole calculation 2.99 9 7.00 4 0 1.00 0 Reject Mark Question Number 23(b)(i) Peak at m/e = 89 labelled M+ Acceptable Answers ALLOW Any clear label e.g. C3H7O2N+ Question Number 23(b)(ii) Mr = 89 = Mr (C3H7O2N) so molecular Acceptable Answers formula is C3H7O2N Symbols in any order IGNORE structural and displayed formulae Reject Mark Answer with no explanation Mr = 90 C3H7O2N+<br />

Question 21 22 23 24

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