2024 EJC H1 Chemistry Prelims P2 Solutions (for exchange)

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2024 General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CIVICS GROUP 2 3 – INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 8873/02 10 September 2024 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not use paper clips, highlighters, glue or correction fluid. Write your name, civics group, registration number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Section A Answer all questions. Section B Answer one question. The number of marks is given in brackets [ ] at the end of each question or part question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A 1 / 11 2 / 15 3 / 11 4 / 11 5 / 12 Section B 6 / 7 / 20 Total / 80 This document consists of 24 printed pages.

2 © EJC 8873/02/J2Prelims/24 For Examiner’s Use Section A Answer all questions in this section. 1 This question is regarding Period 3 elements. (a) The second ionisation energy shows a general increase across Period 3 of the Periodic Table, from Mg to Ar. (i) Define the term second ionisation energy. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [1] (ii) Write an equation to represent the second ionisation energy of silicon. ................................ ................................ ................................ ......................... [1] (iii) State the electronic configurations of Si+ and Al+. Hence, explain why the second ionisation energy of silicon is found to be lower than that of aluminium. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] (b) The second ionisation energies of 8 successive elements F to M from both Periods 2 and 3 of the Periodic Table are shown in Fig. 1.1. Fig. 1.1 Si+(g) → Si2+(g) + e– The second ionisation energy is the energy required to remove 1 mole of electrons from 1 mole of singly charged gaseous cations to form 1 mole of doubly charged gaseous cations. Si+: 1s2 2s2 2p6 3s2 3p1 Al+: 1s2 2s2 2p6 3s2 The 3p electron to be removed from Si+ is at a higher energy level than the 3s electron to be removed from Al+. Hence, less energy is required to remove the 3p electron from Si+. ×E

3 © EJC 8873/02/J2Prelims/24 [Turn over For Examiner’s Use (i) Explain why there is a sudden drop in the second ionisation energy from element H to I. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] (ii) Identify the element which represents silicon. ................................ ................................ ................................ ......................... [1] (iii) Element E has one proton less than element F. Using a cross ‘×’, plot the relative position of the second ionisation energy of element E on Fig. 1.1. [1] (c) (i) State the formulae of the chlorides of the elements Na to P where the element is in its highest oxidation state. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [1] (ii) The chlorides of Si and P in (c)(i) react with water. Write an equation for each reaction and state the expected pH of the products. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] [Total: 11] NaCl, MgCl2, AlCl3, SiCl4, PCl5 SiCl4(l) + 2H2O(l) → SiO2(s) + 4HCl (aq) ; pH of solution is 2 PCl5(s) + 4H2O(l) → H3PO4(aq) + 5HCl(aq) ; pH of solution is 2 K The second electron to be removed from I is from a Principal Quantum Shell/ electronic shell which is further away from the nucleus, as compared to that from H. Hence, the 2nd I.E. of I is much smaller as the second electron removed from I is less strongly attracted to the nucleus. Hence, lesser amount energy is needed to remove the second electron.

4 © EJC 8873/02/J2Prelims/24 For Examiner’s Use 2 Phosgene, Cl2C=O, is a colourless, toxic gas. It is used in the production of pesticides, rubbers and adhesives. (a) In phosgene, the carbon atom is in the centre of the molecule and is attached to both chlorine atoms and oxygen atom. (i) Draw the dot-and-cross diagram of the phosgene molecule. [1] (ii) State and explain, with reference to the Valence Shell Electron Pair Repulsion theory, the shape of a phosgene molecule. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ............................. ................................ ................................ ................................ ......................... [2] (iii) Suggest the Cl–C–Cl bond angle in the COCl2 molecule. ................................ ................................ ................................ ......................... [1] Electron pairs such as lone pairs and bond pairs around the central atom arrange themselves to be as far away from each other as possible to minimise inter- electronic repulsion. There are 3 bond pairs and no lone pairs around the central atom in COCl2, hence giving a trigonal planar shape. 120o

5 © EJC 8873/02/J2Prelims/24 [Turn over For Examiner’s Use (b) Table 2.1 shows the electronegativity values of the atoms in phosgene. Table 2.1 atom electronegativity/Pauling units carbon 2.5 chlorine 3.0 oxygen 3.5 (i) Explain what is meant by electronegativity. ................................ ................................ ................................ ............................. ..........................