JPJC 2022 JC1 promos P2 Suggested Answer

 Jurong Pioneer Junior College [Turn Over JURONG PIONEER JUNIOR COLLEGE 2022 JC1 YEAR END EXAMINATION Higher 2 CANDIDATE NAME CLASS 2 2 S EXAM INDEX CHEMISTRY 9729/02 Paper 2 Structured and Free Response Questions 28 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams, graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in Section A (55 marks) and in Section B (20 marks) in the spaces provided on the Question paper. For Section B, if additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 7 2 13 3 8 4 14 5 13 Section B 6 20 Penalty (delete accordingly) Lack 3sf in final answer –1 / NA Missing/wrong units in final answer –1 / NA Total 75 This document consists of 19 printed pages and 3 blank pages.

2  Jurong Pioneer Junior College 9729/02/J1 YEAR END EXAM/2022 Section A (55 marks) Answer ALL the questions in the spaces provided. 1 Atoms contain the subatomic particles – electrons, protons and neutrons. Protons and electrons were discovered by observations of their behaviours in electric field. For Examiner’s Use (a) Fig. 1.1 Fig. 1.1 shows the behaviour of separate beams of protons and neutrons in an electric field. (i) Complete the diagram in Fig. 1.1 with the relative charge of each of the electrically charged plates. [1] (ii) In Fig. 1.1, show how a separate beam of electrons from the same source behaves in the same electric field. [1] (iii) If the particles are all travelling at the same speed, through an electric field of constant strength, the angle of deflection is proportional to their charge/mass ratio. In this particular experimental set-up, protons are deflected through an angle of +15. Assuming an identical set of experimental conditions, calculate the angle of deflection for 4He2+. charge mass angle of deflection proton 1+ 1 +15 4He2+ 2+ 1+ 4 2 ½  (+15) = +7.50 (sign + 3sf + units) [1] charge on plate …………………… negative electrons protons charge on plate …………………… source neutrons positive  deflects more in the opposite direction relative to proton  parabolic only within electric field (width of plate)

3  Jurong Pioneer Junior College 9729/02/J1 YEAR END EXAM/2022 [Turn Over Under identical conditions, a beam of particles, A, each having 12 times the mass of a proton, was deflected by an angle of +5. For Examiner’s Use (iv) Suggest the overall charge on a particle of A. charge mass angle of deflection proton 1+ 1 +15 A q 12 q 12 (+15) = +5  q+ = 4+ ……………. [1] (v) Given that a particle of A contains 6 protons, deduce the number of neutrons and electrons in a particle of A. Recall:  mass of a proton = mass of a neutron  electron is very light (mass of an electron << mass of a proton or a neutron) so mass of cation A = mass of protons and neutrons Since cation A contains 6 protons and has an ionic charge of 4+, number of neutrons = 12 – 6 = 6 and number of electrons = 6 – 4 = 2. number of neutrons ………………. number of electrons ……………… [2] (b) Hydron is a general term used to represent the ions 1 1H , 2 1H and 3 1H . State, in terms of subatomic particles in the nucleus, what is the same about each of these ions and what is different. same ……………………………………………………………………………………. different ………………………………………………………………………………… [1] [Total: 7] 4+ (sign after number for charge) 6 2 number of protons number of neutrons

4  Jurong Pioneer Junior College 9729/02/J1 YEAR END EXAM/2022 2 (a) Group 1 chlorides are white crystalline solids. Fig 2.1 shows the structure of the simplest repeat unit in a crystal of lithium chloride and in a crystal of caesium chloride. In LiCl, each Li+ ion is surrounded by six Cl ions. In CsCl, each Cs+ ion is surrounded by eight Cl ions. Fig 2.1 For Examiner’s Use (i) Explain why the ionic radius of the Group 1 cations increases down the group. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. [1] (ii) NaCl and KCl have the same crystal structure as LiCl. Suggest why CsCl has a different crystal structure. …………………………………………………………………………………….. …………………………………………………………………………………….. [1] Concept check: CsCl is ionic (Read info given in qn stem!) so it is incorrect to mention Cs can form more bond pairs or can expand octet which involves formation of covalent bonds. LiCl CsCl The effects of increasing number of principal quantum shells AND increasing shielding outweigh the effect of increasing nuclear charge. Hence, nuclear attraction on outermost electrons decreases so ionic radius decreases. Cs+, having a much larger radius than Na+ and K+ so more Cl ions can fit/pack around (or surround) each Cs+ ion. Consider the effect of each factor on radius 1. no. of p.q.s.   radius  2. shielding   radius  3. nuclear charge   radius  Since the trend shows increasing radius, combined effects of factor 1 and 2 outweigh effect of factor 3. cation anion

5  Jurong Pioneer Junior College 9729/02/J1 YEAR END EXAM/2022 [Turn Over (b) The distance between the centres of two adjacent ions in a crystal structure can be calculated by using the equation shown. interionic distance = cation radius + anion radius Table 2.2 shows some information about 3 different ionic solids. Table 2.2 ionic solid lattice energy / kJ mol1 cation radius / nm anion radius / nm cation charge anion charge crystal structure LiCl 853 0.076 0.181 +1 1 see Fig 2.1 NaCl 771 0.095 0.181 +1 1 same as LiCl MgO 3899 0.065 0.140 +2 2 same as LiCl Use the information in Table 2.2 to state the two factors that determine the numerical magnitude of lattice energy and deduce which factor has the greater effect. Explain your answer. For Examiner’s Use ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. [2] (c) The solubility of ionic solids varies according to the solvent used. Both water and hexane are solvents. (i) Draw a labelled diagram to show the significant force of attraction between two water molecules. Include the name of attraction in your diagram. [2] Correct drawing of hydrogen bonds, showing:  (+, ) on O–H+ bond of one H2O molecule  lone pair on O atom of the other H2O molecule with (+, ) on O–H+ bond  dotted line from lone pair on O atom to the H atom of the other H2O molecule  Indicate & label ‘hydrogen bond’ Magnitude of LE is affected by (q+ × q) and (r+ + r) (or       q qLE r r ). Compared to NaCl, LiCl has same (q+ × q) and smaller (r+ + r) which causes LE of LiCl to be slightly larger in magnitude than that of NaCl. Compared to NaCl, MgO has larger (q+ × q) and smaller (r+ + r) which causes LE of MgO to be MUCH larger in magnitude than that of NaCl. Hence, (q+ × q) has a great