Skip to content
CIE Nov 2015 v3 Paper 4 Q2
Answers available below
Show answer
Question
1
2
3
4
5
6
7
8
9
10
![(a) Cobalt is a transition element and forms compounds with oxidation numbers +2 and +3. Complete the electronic structures for a cobalt atom, 1s22s22p6 cobalt in the +3 oxidation state. 1s22s22p6 PMT [2] (b) (i) In an aqueous solution of cobalt(II) sulfate the cobalt forms complex ions. What is meant by the term complex ion?[1] (ii) State two chemical properties of cobalt, other than the formation of complexes, that are not shown by a typical s-block element.[2] (c) Cobalt(II) ions, Co2+(aq), show some chemical properties similar to those of copper(II) ions, Cu2+(aq). Use this information and the Data Booklet to suggest the formula of the cobalt species formed in each of the following reactions. State the type of reaction taking place in each case. formula of cobalt species formed type of reaction Co2+(aq) + an excess of NH3(aq) Co2+(aq) + OH(aq) Co2+(aq) + S2O8 2(aq) [5]UCLES 2015 9701/43/O/N/15<br />
PMT (d) Some transition elements are present in superconductors. These are materials that conduct electricity with little or no resistance. Compound Q is a superconductor and contains 13.4% yttrium, 41.2% barium, 28.6% copper and 16.8% oxygen by mass. (i) Show that the empirical formula of Q is YBa2Cu3O7. Show all your working. (ii) The table shows the oxidation numbers of yttrium, barium and oxygen in Q. element oxidation number yttrium barium oxygen +3 +2 2 Calculate the average oxidation number of copper in Q. (iii) Hence deduce the oxidation number of each of the three copper atoms in Q. [1] [1] [1] [Total: 13]UCLES 2015 9701/43/O/N/15 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/November_2015_v3_QP_-_Paper_4_CIE_Chemistry_A-level_2-0.jpg)
![Page 2 Mark Scheme Syllabus Paper Cambridge International A LevelOctober/November 2015 9701 43 Question Marking Point Marks Total Marks PMT (a) ionic bonds break / bonds between Mg 2+ and Cl - break forces / bonds / attractions form between the ions and water (b) (i) (the energy change) when 1 mole of a substance dissolves in water / becomes aq (ii) 2+ H latt MgCl 2 + H sol MgCl 2 = H hyd Mg + 2H lhyd Cl 2524155 = 1925 + 2H = 377 kJ mol 1 hyd Cl (iii) magnesium / Mg is higher charge / sodium / Na is smaller charge magnesium / Mg is smaller / sodium / Na is larger Mg stronger attraction for water / Na weaker attraction for water any two (c)solubility decreases lattice energy and hydration enthalpy decreasehydration enthalpy decreases more rapidly / is dominant factorso (enthalpy change of) solution becomes less exothermic / more endothermic (a) Co 3s 3p 3d 4s 3+ Co 3s 3p 3d (b) (i) atom or ion, bonded to (one or more), ligands (ii) any two from: two (or more) oxidation states, catalytic activity, coloured ions or compoundsCambridge International Examinations 2015 [Total: 11] [1] [1]<br />
Page 3 Mark Scheme Syllabus Paper Cambridge International A LevelOctober/November 2015 9701 43 Question Marking Point (c) transition element type of reaction Marks Total Marks PMT 2+ Co (aq) + an excess of NH3(aq) species formed [Co(NH3)6] or 2+ 2+ [Co(NH3)4] or [Co(NH3)4(H2O)2] 2+ ligand exchange 2+ Co (aq) + OH (aq) Co(OH)2 or precipitation or Co(OH)2(H2O)4 acid-base 2+ Co (aq) + S2O8 2 (aq) [Co(H2O)6] or 3+ 3+ Co or Co2(SO4)3 redox or oxidation or reduction of S2O8 2 (d) (i) Y 13.4 / 88.9 or 0.15 Ba 41.2 / 137 or 0.3 Cu 28.6 / 63.5 or 0.45 O 16.8 / 16 or 1 (ii) = 7 / 3 or (+) 2.3 (iii) two Cu are + 2 and one Cu is + 3 [Total: 13]Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/November_2015_v3_MS_-_Paper_4_CIE_Chemistry_A-level_2-0.jpg)
