ACSBR 4NA 5105 2024 SCCHEM prelim ANS FINAL

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4 Page 1 ANSWERS TO 2024 PRELIM 5105 SCCHEM Paper 3: 1. B 16. A 2. D 17. C 3. B 18. C 4. B 19. C 5. B 20. B 6. A 7. B 8. B 9. A 10. C 11. D 12. C 13. A 14. A 15. C Paper 4: Section A Answer all the questions in this section. 1 One of the isotopes of bromine has the symbol shown. Br35 79 (a) Complete the table to show the relative mass and relative charge of the particles found in this isotope. particle relative mass relative charge electron 1/1836 OR 1/1840 1- proton 1 1+ neutron 1 0 1 mark for at least 2 correct; 2 marks for all correct; [2]

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4 Page 2 (b) Determine the number of each of these particles in one atom of the isotope of bromine, Br35 79 . number of electrons = ……… 35………………… number of neutrons = ……… 44………………… number of protons = ……… 35………………… [2] 1 mark for at least 2 correct; 2 marks for all correct; 2 The diagram shows how the components in petroleum (crude oil) can be separated into different fractions using fractional distillation. (a) Which of the fractions, A, B, C or D has the highest boiling point? …… D OR BITUMEN…………………………..… …… ………………………………. [1] (b) Suggest one compound likely to be present in fraction A. Methane/CH4/ethane/C2H6/propane/C3H8/butane/C4H10. ..………… [1] (c) Some fractions like diesel oil, which contain larger molecules, can be broken up into smaller molecules by a chemical reaction. C16H34 → substance E + C2H4 + C3H6 (i) Name the chemical reaction. …………… cracking…………………..……………………………….. [1] (ii) Deduce the chemical formula of substance E. ………………… C11H24……………………………………………….. [1]

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4 Page 3 (iii) Name and draw the structural formula of C3H6. name ……… propene………. structural formula [2] (iv) C2H4 can act as monomers to undergo polymerisation to form polyethene. Complete the structure of polyethene. [1] (d) Bioethanol is produced from sugarcanes and is considered an alternative renewable energy source to fossil fuels like petroleum. The following description for the use of bioethanol is in a student’s notebook. Some words have been left out. Complete the description by writing in the missing words. The use of bioethanol is often described to be environmentally sustainable or even ‘carbon neutral’, as it does not increase the levels of carbon dioxide in our atmosphere. Bioethanol fuel is obtained through fermentation of sugar/glucose, which is obtained during photosynthesis in sugarcane which absorbs atmospheric carbon dioxide. This volume of carbon dioxide absorbed in the production of bioethanol offsets the volume of carbon dioxide produced in the combustion/burning of bioethanol. [3]

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4 Page 4 3 The diagram shows two versions of the Periodic Table where hydrogen is either placed in Group 1 or not with any group. version 1 1 2 H Li Na K version 2 1 2 13 14 15 16 17 18 H (a) With reference to version 1 of the Periodic Table, give a reason why hydrogen can be placed in the same group as the other elements in Group 1. Hydrogen has one valence/outer shell/outermost shell electron (in its atom) OR hydrogen can form an ion of 1+ charge (just like elements in Group 1). [1] (b) With reference to version 2 of the Periodic Table, state one difference between the physical properties of hydrogen and the other elements in Group 1. Any one: 1. Hydrogen has a lower boiling point than elements in Group 1. 2. Hydrogen exists as a gas at room temperature and pressure while elements in Group 1 exist as solids. 3. Hydrogen is a poor conductor of heat (or electricity) while elements in Group 1 are good conductors of heat (or electricity). 4. Hydrogen has a lower density than elements in Group 1. REJECT chemical properties comparison or no comparison at all. [1] (c) Margarine is manufactured by passing hydrogen through polyunsaturated vegetable oils to form a solid product. (i) State the type of reaction involved in this process. ……… addition……………………………..……………………………….. [1] (ii) State what is meant by the term polyunsaturated. … (Vegetable oils) contain several C=C double bonds……….. [1]

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4 Page 5 (d) Hydrogen was reacted with oxygen to form water. (i) Calculate the number of moles of 225 g of water. [Ar: H, 1; O, 16] Show your working. No. of moles of water = 225 / 18 1 mark for working shown; 1 mark for final answer below; number of moles of water = …… 12.5……. [2] (ii) Sodium from Group 1 can react with water to form sodium hydroxide and hydrogen gas. Complete the equation for this reaction. 2Na + 2H2O  2NaOH + H2 1st mark is for the 3 substances formula; only when 1st mark is obtained, 2nd mark is for balancing equation; [2] Section B Answer one question from this section. 4 Pentadecane, C15H32, can under combustion under different conditions to give different products. condition supply of oxygen products 1 excess gas P and water vapour 2 limited gas P, gas Q and gas R (a) (i) Identify gas P and state the observation when gas P is bubbled through limewater. gas P ……. … carbon dioxide / CO2… … …………………………... .......... observation ..… white precipitate formed in limewater............. [2] (ii) Methane and gas P have similar effects on the environment. Describe the effect of an increased level of methane on the environment. ….. cause (global warming) more extreme weather events (such as flooding) OR melting of polar ice. [1] (iii) Given that gas P is an acidic gas, state the colour change when gas P is bubbled into Universal indicator solution. colour changes from …… green……… to ……. yellow/orange/red……. [1] (b) Gas Q is a toxic gas and can be formed by the incomplete combustion of pentadecane. (i) Identify gas Q. ……… carbon monoxide / CO…… [1] (ii) 210 cm3 of oxygen is required to completely combust a certain volume of pentadecane. Calculate the minimum volume of air needed at room temperature and pressure. Volume of air = 210/21 × 100 volume of air = … 1000………… cm 3 [1]

Preliminary Examination 2024 Secondary Four Normal (Academic) Science (Chemistry) 5105 Paper 4