YCKSS Prelim Ans

YIO CHU KANG SECONDARY SCHOOL PRELIMINARY EXAMINATION 2024 SECONDARY FOUR EXPRESS CHEMISTRY 6092 ANSWER SCHEME PAPER 1 1 D 11 B 21 D 31 B 2 C 12 A 22 D 32 D 3 C 13 B 23 C 33 C 4 B 14 B 24 D 34 D 5 D 15 B 25 D 35 D 6 C 16 A 26 A 36 B 7 C 17 B 27 D 37 D 8 A 18 B 28 B 38 A 9 B 19 C 29 A 39 C 10 D 20 D 30 C 40 C

2 4E PRELIM EXAM 2024 6092 PAPER 2 SECTION A Qn Answers Marks A1 (a) Si [1] (b) Ar [1] (c) I [1] (d) N/ P/ As [1] (e) Ni [1] (f) S and O / N and O [1] Total : [6] A2 (a) No. of mol of sulfuric acid = 0.0005 mol ; No. of mol of sodium hydroxide = 0.001 mol ; Concentration of sodium hydroxide = 0.001/0.01; = 0.1 mol/dm3 ; ;;[1] Max [2] (bi) 10 cm 3 [1] (bii) ethanoic acid is monobasic while sulfuric acid is dibasic / ethanoic acid produces one mole of hydrogen ions while sulfuric acid produces 2 moles of hydrogen ions per mole of acid. To neutralise the same number of moles of NaOH, twice the volume of ethanoic acid is required compared to sulfuric acid given that the concentration of acid used is the same. [1] (c) A strong acid completely ionises in water while a weak acid partially ionises in water. [1] H2SO4 (aq)  2H+ (aq) + SO42- (aq) CH3COOH (aq) CH3COO- (aq) + H+ (aq) equations [1] ignore state symbols [2] Total : [6]

3 4E PRELIM EXAM 2024 6092 Qn Answers Marks A3 (a) Diamond has the highest resistivity as it does not conduct electricity. All its valence electrons are used in covalent bonding. No mobile/delocalised electrons present to conduct electricity. [1] The three precious metals have low resistivity as they are good conductors of electricity. They have a sea of delocalised/mobile electrons that act as charge carriers in their giant metallic lattice structure. [1] Accept : free electrons [2] (b) No. I do not agree with student’s comment. Graphite’s resistivity value will be closer to the metals because graphite has mobile/delocalised electrons in its structure that makes it a good electrical conductor. [1] (c) Pure metals are too soft to be sold commercially / alloys are harder. [1] In alloys, the different-sized atoms disrupt the regular arrangement of the atoms of pure metal. A larger force is required for the layers of atoms to slide over each other. [1] [2] (d) Resistivity of metals and graphite increases with increasing temperature [1] As temperature increases, metal ions/carbon atoms gain energy and vibrate faster / more vigorously. The increased vibrations