2024 CGS Chemistry Prelim Paper 1 Mark Scheme

ANSWER KEY READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluids. Write your name, index number and class on the Answer Sheet in the spaces provided. DO NOT WRITE ON ANY BARCODES. There are forty questions on this paper. Answer all questions. For each question, there are four possible answers, A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the OTAS sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet A copy of the Periodic Table is printed on page 19. The use of an approved scientific calculator is expected, where appropriate. This booklet consists of 19 printed pages, including the cover page. CRESCENT GIRLS’ SCHOOL SECONDARY FOUR PRELIMINARY EXAMINATION 2024 CHEMISTRY Paper 1 Multiple Choice Additional Materials: Multiple Choice Answer Sheet 6092/01 28 August 024 1 hour

2 1 2 3 4 5 6 7 8 9 10 B C D C A C B A D B 11 12 13 14 15 16 17 18 19 20 C A D A C D C C A B 21 22 23 24 25 26 27 28 29 30 C A D C B B A D A B 31 32 33 34 35 36 37 38 39 40 C D A A B C C B B C 1 A student measures the rate of the reaction between marble chips, CaCO3, and dilute hydrochloric acid. CaCO3 + 2HCI → CaCl2 + CO2 + H2O Which diagrams show apparatus that are suitable for this experiment? A 1 and 2 B 1, 2 and 4 C 2 and 3 D 2, 3 and 4

3 2 Chromatograms of a urine sample using two different solvents are shown below. Based on the two chromatograms, which drug(s) is/are present in the urine sample? A drug P only B drug Q only C drugs P and Q only D drugs P, Q and R 3 Since the discovery of graphite, scientists have been able to extract a single layer of carbon atoms (known as graphene) and convert it to another material known as graphane by attaching one hydrogen atom to each carbon atom as shown below. Graphane has the same hexagonal-ring structure as graphene and retains most of its properties too. Which properties of graphene is not likely to be shared by graphane? A It is insoluble in water. B It is very strong. C It has a high melting point. D It is an electrical conductor.

4 4 An isotope of element Z has 20 neutrons and 17 protons. Which is the correct symbol for an ion of the isotope of element Z? A 𝐙𝟏𝟕 𝟏𝟖 + B 𝐙𝟏𝟕 𝟏𝟖 - C 𝐙𝟏𝟕 𝟑𝟕 - D 𝐙𝟏𝟖 𝟑𝟕 - 5 Hydrogen is able to form compounds with metals and non-metals. The formulae of some of these compounds are shown below. CH4 HCl MgH2 KH What is the order of melting point of these compounds? lowest melting point highest melting point A CH4 HCl KH MgH2 B CH4 HCl MgH2 KH C HCl CH4 MgH2 KH D KH MgH2 HCl CH4 6 The heating curves (not drawn to scale) of nitrogen and oxygen over a period of time are shown in the graph. At which temperature will there be two different states of matter co-existing at the same time, in a mixture of nitrogen and oxygen under similar conditions? A – 180 °C B – 200 °C C – 215 °C D – 220 °C

5 7 The diagram below shows the bonding between P and Q in the covalent molecule, PQ2. What are the electronic structures of atoms P and Q before combining together to form the above molecule? P Q A 2.8 2.8.8 B 2.6 2.8.7 C 2.6 2.8.6 D 2.4 2.8.7 8 0.1 mole of a chloride XCl2 combines with 10.8 g of water to form the hydrated salt, XCl2.nH2O. What is the value of n? A 6 B 8 C 10 D 12 9 Ammonia reacts with chlorine according to the equation shown below: 2NH3 (g) + 3Cl2 (g) → N2 (g) + 6HCl (g) If 90 cm3 of ammonia is mixed with 60 cm3 of Cl2 and all the volumes were measured at room temperature and pressure, what is the total volume of gases at the end of the reaction? A 20 cm3 B 120 cm3 C 140 cm3 D 190 cm3

6 10 When 4.8g of magnesium is heated in a crucible, 5.9g of magnesium oxide is formed. What is the percentage yield of magnesium oxide? A 53% B 74% C 80% D 81% 11 A student is given two samples, one of which is aluminium oxide and the other is magnesium carbonate. He needs to find a method to identify the two samples. Which of the following show(s) the correct method(s) and observation(s)? method observation(s) 1 add nitric acid only aluminium oxide dissolves 2 add nitric acid both samples dissolve. Effervescence is observed in the reaction with magnesium carbonate 3 add sodium hydroxide only aluminium oxide dissolves 4 add sodium hydroxide both samples dissolve. Effervescence is observed in both the reactions A 1 and 4 only B 2 only C 2 and 3 only D 3 only

7 12 Butterfly pea flower extract is commonly used in drinks nowadays and it changes colour according to different pH values. The table below shows the colours of butterfly pea flower extract at different pH values. pH range colour 0 – 3 violet 4 – 8 blue 9 – 11 green 12 – 14 yellow Which pair of substances can be distinguished by adding butterfly pea flower extract to each substance separately? A acid rain and aqueous sodium chloride B aqueous ammonia and limewater C aqueous sodium sulfate and aqueous sodium chloride D dilute hydrochloric acid and dilute sulfuric acid 13 Which of the following reactions will produce the least amount of carbon dioxide? A sodium carbonate and hydrochloric acid B copper(II) carbonate and hydrochloric acid C magnesium carbonate and sulfuric acid D lead(II) carbonate and sulfuric acid 14 The table below shows the results of some tests carried out on separate portions of a solution M. test observation aqueous sodium hydroxide added test-tube feels warm and no precipitate forms acidified aqueous silver nitrate added white precipitate forms What could be the identity of solution M? A hydrochloric acid B potassium sulfate C sodium chloride D zinc sulfate

8 15 A student stated that since low temperatures produce a greater yield of ammonia, the reaction should be carried out at 50oC instead of 450oC. Which of the following statements best explains why the reaction is not carried out at 50oC? A Ammonia is unstable at 50oC. B The reactants are unstable at 50oC. C The reaction is too slow at 50oC. D The reaction mixture is easily separated at higher temperatures. 16 Ammonium chloride is heated strongly in a boiling tube. Damp blue and red litmus papers were placed at the mouth of the boiling tube for the gases produced. Which of the following is the correct sequence of observations that would be made? first observed colour change final colour of both litmus papers A The damp blue litmus paper turns red. red B The damp blue litmus paper turns red then bleaches. white C The damp red litmus paper turns blue. blue D The damp red litmus paper turns blue. red 17 Which are redox reactions? 1 HCl + NaOH → NaCl + H2O 2 Zn + 2HNO3 → Zn(NO3)2 + H2 3 Ag2SO4 + 2NaCl → 2AgCl + Na2SO4 4 2Fe2+ + Cl2 → 2Fe3+ + 2Cl- A 1, 2 and 3 B 1 and 3 C 2 and 4 D 3 and 4

9 18 Dry hydrogen gas is passed over a heated powdered solid and then through a cooled U-tube before the excess of hydrogen is burned in air. A colourless liquid collects in the U-tube. What could the powdered solid be? A aluminium oxide B copper(II) oxide C iron(III) oxide D magnesium oxide 19 Equal masses of different metals 1 to 4 are placed in the test tubes co