Edexcel Jan 2012 Paper 1 Q24 (with explained solutions) |

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Edexcel Jan 2012 Paper 1 Q24

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PMT 24 (a) Briefly describe an experiment, with a diagram of the apparatus you would use, which shows that there are oppositely charged ions in copper(II) chromate(VI), CuCrO4. Describe what you would expect to see. Formula of ion Cu2+(aq) CrO4 2(aq) Colour blue yellow (4) Diagram(b) The ions in an ionic lattice are held together by an overall force of attraction. (i) Describe the forces of attraction in an ionic lattice. (1)(ii) Suggest two forces of repulsion which exist in an ionic lattice. (2)18 *P39295A01824*<br />
PMT (c) Part of the Born-Haber cycle for magnesium oxide, MgO, is shown below. Mg2+(g) + O(g) Mg2+(g) + O2(g) Mg(g) + O2(g) Mg(s) + O2(g) MgO(s) (i) Complete the empty box with the appropriate formulae and state symbols. (ii) Identify the enthalpy changes represented by the letters A and C. (2) (2) AC(iii) Give the expression for the enthalpy change F in terms of the other enthalpy changes A to E. (1) F = *P39295A01924* 19 Turn over<br />
PMT (d) The lattice composed of the ions Mg2+ and O2 is stronger than a lattice composed of the ions Mg+ and O . (i) Explain, in terms of the charges on the ions and the size of the cations, why this is so. (2)(ii) Suggest how the lattice energy of Mg2+O2 would differ from that of Mg+O. (1)(Total for Question 24 = 15 marks) 20 *P39295A02024*<br />

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Question Number 24(a) Acceptable Answers Reject Mark First mark: Diagram showing U-tube OR filter paper on a microscope slide OR electrodes in a beaker OR other feasible set-up such as but a + and asign must be shown somewhere on the diagram by signs or words, positive and negative. NOTES If set-up in the picture above is used, in addition to the + andsigns a bridge between the two beakers must also be shown. External circuits do not have to be complete (e.g. wires can be shown attached to a slide, provided the + andlabels included). If the words cathode and/or anode are included, for the first mark to be awarded the cathode must be shown as ve and/or the anode as +ve If a battery symbol shown, IGNORE any incorrect polarities, that is IGNORE any electrode materials EXCEPT Cu2+ and/or CrO4 2 (1) +6CH0101 1201<br />
Second mark: Description to include the idea that the ions move/ions are mobile/ions migrate MUST BE IN WORDS ALLOW if description focuses on the movement of one of the ions to the oppositely-charged electrode (1) 2 Third mark: Yellow ion/yellow (colour)/CrO4 moves towards the/+ve (electrode)/ anode (1) Fourth mark: Blue ion/blue (colour)/Cu2+ moves towards cathode /ve (electrode) (1) Mark CQ on candidates cathode and anode signs for the 3rd and 4th marks Just ions are attracted to the electrodes of opposite charge Mark Mark Question Number 24(b)(i) Acceptable Answers Reject (Forces of attraction between) oppositely-charged ions/positive and negative ions/cations and anions IGNORE comments about electron transfer Just ionic bonds/ Just electrostatic forces of attraction Acceptable Answers Question Number 24(b)(ii) First mark: Reject Ions of the same charge (repel)/ positive ions (repel)/negative ions (repel) (1) Second mark: Nuclei (of the ions repel) ALLOW protons (in the ions repel) OR Electron clouds OR electrons (in the ions repel) (1) Magnetic repulsion negates first mark Electrons repel nuclei 6CH0101 1201<br />
Acceptable Answers Question Number 24(c)(i) Mg2+(g) (1) O2 (g) (1) Penalise missing /incorrect state symbols once only Max 1 if include 2e Reject Mark Question Number 24(c)(ii) Mark Acceptable Answers Reject (A is enthalpy change of) formation (of MgO) (1) ALLOW just Hf ALLOW (enthalpy change of) combustion of magnesium (C is) (sum of) first plus second ionization energies (of Mg) / IE1 + IE2 (for Mg) (1) ALLOW first and second ionization energies (of Mg) IGNORE references to standard (enthalpy change of) reaction Just ionization energy/ second ionization energy (of Mg) Acceptable Answers Question Number 24(c)(iii) (F =) ABCDE Reject Mark NOTE: These letters may be in any order, but the signs MUST be correct ALLOW answers when the enthalpy changes are identified correctly in words or symbols in lieu of the letters 6CH0101 1201<br />
Reject Mark Acceptable Answers Question Number 24(d)(i) First mark: Any mention of intermolecular forces scores (0) overall for this question Mg2+ AND O2 higher charge / Mg2+ AND O2 higher charge density (than Mg+ and O) NOTE: both ions needed (1) Second mark: Mg2+ smaller (than Mg+) (1) IGNORE comparisons of the relative sizes of O with O2 even if INCORRECT IGNORE any references to polarization (of ions) and/or covalent character Acceptable Answers Question Number 24(d)(ii) (Lattice energy of Mg2+O2- is) more exothermic/more negative ALLOW greater/increased/higher/ more/larger/bigger IGNORE stronger lattice Reject Mark energy required OR Lower/less/ smaller 6CH0101 1201<br />
N.B. Throughout, ALLOW C2H6 for CH3CH3 and C2H5Cl for CH3CH2Cl and C2H5 for CH3CH2 and C4H10 for CH3CH2CH2CH3 etc If CH4 used instead of CH3CH3 max (1) mark overall for (a)(i) and (a)(ii) taken together Then mark (a)(iii) and (a)(iv) CQ as for CH4 IGNORE positions of the dots in free radicals; dots must be shown in each radical Acceptable Answers Question Number 25(a)(i) CH3CH3 + ClCH3CH2+ HCl Reject OR CH3CH2+ Cl2CH3CH2Cl + Cl Acceptable Answers Question Number 25(a)(ii) CH3CH2+ Cl2CH3CH2Cl + Cl Reject OR CH3CH3 + ClCH3CH2+ HCl N.B. different answers for (i) and (ii) needed Mark Mark Acceptable Answers Question Number 25(a)(iii) 2CH3CH2CH3CH2CH2CH3 Reject Mark Cl + ClCl2 OR CH3CH2+ ClCH3CH2Cl Acceptable Answers Question Number 25(a)(iv) CH3CH2+ ClCH3CH2Cl Reject Mark OR 2CH3CH2CH3CH2CH2CH3 N.B. different answers for (iii) and (iv) needed 6CH0101 1201<br />

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