2023 EJC H2 Chemistry Prelims Paper 1 Worked Solutions

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2023 General Certificate of Education Advanced Level Higher 2 CHEMISTRY Paper 1 Multiple Choice 9729/01 21 September 2023 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, civics group and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty 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 separate Answer 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 question paper. The use of an approved scientific calculator is expected, where appropriate. This document consists of 12 printed pages.

2 © EJC 9729/01/J2PE/23 1 D 11 C 21 C 2 C 12 D 22 C 3 A 13 B 23 A 4 B 14 A 24 D 5 B 15 B 25 D 6 D 16 B 26 D 7 C 17 B 27 A 8 A 18 B 28 A 9 A 19 D 29 D 1 A beam of particles contains D‒ and 4He2+. All particles approach an electric field at the same speed. (D is deuterium, 2H) Which row describes the behaviour of the species? D‒ 4He2+ relative extent of deflection A deflect towards (‒) plate deflect towards (+) plate 4He2+ deflected more than D‒ B deflect towards (‒) plate deflect towards (+) plate 4He2+ deflected less than D‒ C deflect towards (+) plate deflect towards (‒) plate 4He2+ deflected more than D‒ D deflect towards (+) plate deflect towards (‒) plate 4He2+ deflected to the same extent as D‒ Answer: D Angle of deflection  𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑎𝑠𝑠 Angle of deflection of D‒  −1 2 Angle of deflection of He2+  +2 4 Thus, He2+ and D‒ are deflected to the same extent, but directed towards plate of opposite charge. beam of particles + ‒

3 © EJC 9729/01/J2PE/23 [Turn over 2 The melting point of calcium, 839 ºC, is much higher than the melting point of sodium, 98 ºC. Which statement is most relevant in explaining this difference? A The calcium atom is larger than the sodium atom. B The calcium atom is heavier than the sodium atom. C The calcium ion, Ca2+, has a higher charge than the sodium ion, Na+. D The calcium ion, Ca2+, contains more electrons than the sodium ion, Na+. Answer: C Calcium and sodium are metals. Their melting points depend on the strength of their metallic bonds. Strength of metallic bonds depend on: • charge of metal ion • size of metal ion • no. of valence electrons which can be delocalised (more delocalised electrons ⇒ greater attraction between metal cations and delocalised electrons) 3 For a fixed mass of an ideal gas, which of the following graphs does not have the same general shape as the rest? (ρ = density of the gas; M = molar mass of gas; T = temperature in Kelvin) A pV against M T B p against ρT C p  against T D T p against V Answer: A =  = == Since , m T n M mpV RTM mpM RT RV charge density (high charge & small size ⇒ high charge density ⇒ stronger attraction for delocalised electrons.)

4 © EJC 9729/01/J2PE/23 Option A Since mpM RTV= , TpV R M= ➔ pV = k T M hence, PV is inversely proportionate to M T (Graph of pV against M T will be a hyperbola graph, i.e., y = 1/x graph) Option B Since pM RT= , p = R M ρ T ➔ p = k ρT (y = mx) Hence, P α ρ T (Graph is an increasing straight line passing through origin) Option C Since pM RT= , P  = R M T ➔ P  = kT (y = mx) Hence, P  α T (Graph is a n increasing straight line passing through origin) Option D Since mpM RTV= , T p = M mR V ➔ T p = kV (y = mx) Hence, T P α V (Graph is an increasing straight line passing through origin) 4 The ammonia molecule can react in various ways: as an acid, as a base, as a nucleophile, as an oxidising agent and as a reducing agent. In which of the following reactions is ammonia reacting as a Brønsted-Lowry acid? A NH3 + H2O  NH + 4 + OH– B NH3 + NaH → NaNH2 + H2 C NH3 + HNO2 → N2 + 2H2O D 2NH3 + NaOCl → N2H4 + NaCl + H2O Answer: B A: Brønsted-Lowry Base since NH3 accepts H+ from H2O to form NH4+ and OH−. B: Brønsted-Lowry Acid. NH3 donates H+ to H− (in NaH) to form NH2− and H2. C: Reducing agent. NH3 is oxidised as oxidation number of N increases from −3 in NH3 to 0 in N2. D: Reducing agent. NH3 is oxidised as oxidation number of N increases from −3 in NH3 to −2 in N2H4.

5 © EJC 9729/01/J2PE/23 [Turn over 5 Which graph shows the correct trend of Period 3 elements and their compounds? A B C D Answer: B Option A shows the trend of 1st IE. The correct graph should be: Option B is correct. Across the period, nuclear charge increases (no. of protons increases) while shielding effecting is approximately constant, leading to an increase in effective nuclear charge. Thus, there is greater electrostatic forces of attraction between the nucleus and valence electrons, electronegativity increases across the period. Option C shows the trend of melting point of period 3 elements. The correct graph for melting point of oxides should be: Option D shows the trend of electrical conductivity of period 3 elements. The correct graph pH of chlorides should be: 11 12 13 14 15 16 17 Proton number 2nd IE

6 © EJC 9729/01/J2PE/23 6 Sulfur is converted to SF6 by fluorine, to SCl2 by chlorine and to S2Br2 by bromine. Which trend does this information best provide evidence for? A electronegativity: F > Cl > Br B first ionisation energy: F > Cl > Br C bond energy: Cl2 > Br2 > F2 D oxidising ability: F2 > Cl2 > Br2 Answer: D Oxidation state of S in SF 6 is +6, SCl2 is +2 and S2Br2 is +1, which correlates with the ability of the halogen to oxidise S. 7 Use of the Data Booklet is relevant to this question. Industrial welding commonly uses a mixture of gases. One such gas mixture composed of 25% argon and 75% of another gas by volume, has a density of 0.572 g dm –3 at standard temperature and pressure. What is the identity of the other gas in the mixture? A oxygen, O2 B hydrogen, H2 C helium, He D carbon dioxide, CO2 Answer: C From density of the mixture, we can obtain the average molar mass of the mixture by multiplying the molar volume at s.t.p. 0.572 x 22.7 = 12.984 g mol–1 Let x be the unknown gas Average molar mass = (0.25 x Ar(Ar)) + (0.75 x Mr(x)) Mr(x) = (12.984 – (0.25 x 39.9)) / 0.75 = 4.012 For Mr of 4.012, the identity is Helium.

7 © EJC 9729/01/J2PE/23 [Turn over 8 Ethanal (CH3CHO) is a colourless gas that is a toxic by-product of ethanol consumption. It undergoes complete combustion as follows: CH3CHO + 5 2 O2 → 2CO2 + 2H2O A sample of 20 cm3 of ethanal was completely combusted with 100 cm3 of oxygen. What will be the final volume of the resultant mixture of gases at 150 ºC? A 130 cm3 B 90 cm3 C 80 cm3 D 40 cm3 Answer: A 20 cm3 of ethanal requires 50 cm3 of oxygen for complete combustion. 50 cm3 of oxygen is left. Since boiling point of water = 100oC, both CO2 and H2O are gases, and since mole ratio = volume ratio for gases under same conditions of temperature and pressure, 40 cm3 of CO2 and 40 cm3 of H2O are formed. The final volume will therefore be 130 cm3. 9 Which of the following processes are always exothermic? 1 Formation of an ionic compound from its gaseous constituent ions 2 Formation of a covalent compound from its constituent elements 3 Dissolving of an ionic compound in water 4