2022 SASS A-Z Chem Prelims Ans Pt1

1 A – Z School’s Preliminary Papers 4 Express Chemistry ANSWERS: Part I A Anderson Secondary School B Beay Secondary School C Chung Cheng High School (Main) D Damai Secondary School E Edgefield Secondary School ANDERSON SECONDARY SCHOOL Paper 1 Paper 2 Qn Answer Marks Comments A1(a)(i) A and F OR B and E 1 (a)(ii) B and D OR C and D Or D and E 1 (a)(iii) A and F 1 (a)(iv) D 1 (b) true false Petroleum is separated by different density into different fractions. ✔ Alkanes used in diesel fuel have a lower boiling point than those used in motor cars. ✔ The fractions used as feedstock for making plastics is extracted from higher up the fractionating column than the fraction used for kerosene(paraffin). ✔ Each fraction contains a mixture of hydrocarbons. ✔ . 2 PRELIM 4E CHEM 2022 6092/01 20 1 2 3 4 5 6 7 8 9 10 A C B D B C C A B A 11 12 13 14 15 16 17 18 19 20 B B A B C D C A C A 21 22 23 24 25 26 27 28 29 30 B C B D B A C B B A 31 32 33 34 35 36 37 38 39 40 C B B A B B B A D B SASChemistry 2022edition

2 A2(ai) C2H4 + H2O → C2H5OH 1 (a)(ii) To increase the percentage yield of ethanol OR To conserve resources and cut down the cost of starting reactants 1 (a)(iii) Oxygen will oxidise ethanol to ethanoic acid / Ethanol formed may undergoes combustion hence reducing the yield of ethanol. 1 (b)(i) 200°C, 80 atm 1 (b)(ii) Optimum temperature is higher so that the reaction between steam and ethene is faster. Optimum pressure is lower because special equipment would be required to maintain the higher pressure which is not cost efficient. 1 1 A3(a) Graphite is made up of many layers of carbon atoms covalently bonded in a hexagonal lattice structure. The layers of carbon atoms are held loosely by weak intermolecular forces of attraction hence the layers can be easily separated using a sticky tape. 1 1 (b) Each carbon atom in graphene has one outer electron that is not used to form covalent bonds. These electrons can move freely and carry electric charges hence graphene has high electrical conductivity. Each carbon atom is covalently bonded to three other carbon atoms. A lot of energy is needed to break these strong covalent bonds hence graphene is strong. 1 1 1 1 (c) Graphene is transparent as it is made up of only a single layer of atoms which is very thin. 1 A4(a)(i) A strong acid completely ionized/ dissociates in aqueous solution/ when dissolved in water while a weak acid partially ionized/ dissociates in aqueous solution/ when dissolved in water. 1 (a)(ii) Tartaric acid is the weaker acid. Universal indicator turns orange in tartaric acid and red in sulfuric acid showing that tartaric acid has a higher pH/ pH of 4-6 while sulfuric acid has a lower pH/ pH of 1-3. Volume of gas collected 10s after reacting