SMSS 2023 Prelim Paper 3 _ 4 ANSWER KEY

Marking Scheme for Paper 3 1 2 3 4 5 6 7 8 9 10 A B D C B B B C D B 11 12 13 14 15 16 17 18 19 20 A A C B D C C D D C Marking Scheme for Paper 4 Section A Qn Answers Marks 1a ZnO 1m each 1b H2 1c Na2O 1d Cl2 2a Z 1m each 2b W and X 2c V or T 2d 1 – correct charges 1 – correct ratio, electrons, particle/ symbol 3a 1 3b Nickel and 200 oC (accept 180 oC) both correct- 1m 3c Bubble both gases into two separate test tube of aqueous bromine. If gas is propene, aqueous bromine turns from reddish brown to colourless. If gas is propane, aqueous bromine remains reddish brown. A: bromine solution 1 – correct indicator 1 – correct colour change for aqueous bromine

3d 1 (2 chlorine atoms must be on 2 diff consecutive carbon atoms) 4a Copper(II) oxide/ copper(II) hydroxide/ copper(II) carbonate R: copper 1 4b Measuring cylinder/ pipette R: beaker 1 4c To obtain a saturated solution (accept: to evaporate most of the water) R: to speed up the reaction 1 4d To ensure that all acid has fully reacted. R: to ensure the acid is fully mixed 1 4ei 137 + 32 + 4 x 16 = 233 R: if units are given 1 4eii 5/233 = 0.02145 mol 1 ecf 4eiii 0.02145 mol 1 ecf 4eiv 0.02145 x [137 + 2(14 + 3 x16)] = 5.60 g 1 ecf 5a Central Business District. Many cars on the road and a lot of carbon dioxide released from the exhaust fumes/ many smokers 1 1 5b Lightning activity/ combustion of fuels at high temperature in car engines. R: cars 1 5c It can cause breathing difficulties/ irritates eyes and skin. 1 5di Place a blue litmus paper into the sample of rainwater. If the blue litmus paper turns red, acid rain is present. OR Add a few drops of Universal Indicator into the sample of rainwater. Universal Indicator changes from green to red/orange when acid rain is present. OR Add a metal. Effervescence is observed. Test for gas with a burning splint which should be extinguished with a ‘pop’ sound. 1 1 1 1 5dii Calcium oxide (lime) / calcium hydroxide (slaked lime) It will neutralise the acid to form salt and water. 1 1 6ai Magnesium 1

6aii Magnesium is able to displace nickel from nickel(II) chloride. R: magnesium is higher up in the reactivity series 1 6aiii Nickel can act as a barrier/ protective layer to prevent oxygen and water from coming in contact with iron. OR Nickel can act as a sacrificial protection, corrode first in place of the iron metal. 1 1 1 1 6bi The limestone decomposes to form calcium oxide. Calcium oxide removes impurity silicon dioxide (A: sand) as slag. 1 1 6bii The carbon atoms/particles are of different size and disrupts the orderly arrangement of iron atoms. Harder for layers of irons atoms/ions/particles to slide past one another easily. 1m max if no mention of atoms/ions/particles 1 1