Greendale 6092/02 Chem Paper 1&2 ANS Prelim 2024

1 2024 Class Preliminary Examination Chemistry Secondary 4 Express Suggested answers Section A 1 2 3 4 5 6 7 8 9 10 D C C D B B C C A D 11 12 13 14 15 16 17 18 19 20 D D B A D A A A C C 21 22 23 24 25 26 27 28 29 30 B C D A D D B B B A 31 32 33 34 35 36 37 38 39 40 D B C A A C A D A C

2 Section B Qn Answer Mark 1(a) acid: hydrochloric acid other reactant: lead(II) nitrate [1] [1] 1(b) nitric acid [1] 1(c) Iron(II) carbonate is added in excess to ensure all the acid is completely reacted / used up. [1] TOTAL [4] 2(a) [1] 2(b) physical: melted, AND cooled AND cut into pellets chemical: cracking to break into smaller molecules [1] [1] 2(c)(i) [1] 2(c)(ii) similarity: The monomer 2 used to make both the polymers is the same dicarboxylic acid, difference: The other monomer used to make this polymer is a diol but the other monomer in (c)(i) is a diamine. [1] [1] 2(c)(iii) (c)(i): amide (linkage) AND Fig. 2.3: ester (linkage) [1] TOTAL [7] 3(a) Same empirical formula AND Mr AND different arrangement of atoms / different units present. [1]

3 Qn Answer Mark 3(b) isomer A: isomer B: [2] 3(c) alcohol: carboxylic acid: [1] [1] 3(d) empirical formula: C3H6O [2] TOTAL [7]

4 Qn Answer Mark 4(a) true false Atoms lose electrons more easily down group 1. ü Melting point decreases from fluorine to iodine. ü The strongest non-metal oxidising agent is at the top of the group. ü Metallic character increases across Period 3. ü [2] 4(b) Comparison of structure: lithium: giant metallic structure graphite: giant molecular structure (consisting of huge network of C atoms) oxygen: simple molecular structure consisting of discrete molecules [1] Comparison of bonding: lithium: strong electrostatic forces between lithium cations and sea of electrons graphite: strong covalent bonds between carbon atoms oxygen: weak intermolecular forces between discrete molecules [1] comparison between the melting points: Most energy needed to overcome the strong covalent bonds between carbon atoms; hence graphite has the highest melting point AND Least energy needed to overcome weak intermolecular forces in oxygen. [1] Electrical conductivity comparison: lithium: presence of delocalised / free moving / mobile electrons to conduct electricity AND oxygen: exist as molecules and no mobile charge carriers / no free moving electrons or ions to conduct electricity [1]

5 Qn Answer Mark graphite: each C atom is bonded to 3 other atoms and 1 free / non-bonded electron per C atom and there are free moving electrons to conduct electricity. [1] TOTAL [7] 5(a) NaH + H2O ® NaOH + H2 [1] 5(b) If the pH of the mixture is less than 10, it is a non-metal hydride; AND If the pH of the mixture is more than 10, it is a metal hydride; [1] 5(c) [2] 5(d) In solid state, ions held in fixed position / no free moving ions to conduct electricity. [1] In molten state, giant (crystal)/ (ionic) lattice structure b