NJC 2026 Prelim P1 Ans

NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME Answer SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 9476/01 17 Sept 2026 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, subject class 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 booklet. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Instructions on how to fill in the Optical Mark Sheet Shade the index number in a 5 digit format on the optical mark sheet: 2nd digit and the last 4 digits of the Registration Number. This document consists of 16 printed pages.

2 NJC SH2 Prelim 9476/1/26 1 The relative abundances of the isotopes of a sample of titanium are shown in the table below. Relative Isotopic Mass 46 47 48 49 50 Relative Abundance 11.2 10.1 100.0 . 7.3 7.0 What is the relative atomic mass of titanium in this sample? A 47.89 B 47.90 C 47.92 D 48.00 Ans: C Relative atomic mass = (46 11.2) (47 10.1) (48 100) (49 7.3) (50 7) 11.2 10.1 100 7.3 7.0  +  +  +  +  + + + + = 515.2 474.7 4800 357.7 350 135.6 + + + + = 6497.3 47.92135.6 = 2 A sample of pure gas is put into a gas syringe at 27.0 οC and 16 kPa. The plunger of the syringe is pushed in to compress the gas, until the volume occupied is halved. After compression, the pressure of the gas is 40 kPa. What is the new temperature of the gas? A 33.8 oC B 67.5 οC C 102.0 οC D 375.0 οC Ans: C Given that n and R are constant (n is constant because the gas did not react), 𝑃1𝑉1 𝑇1 = 𝑃2𝑉2 𝑇2 Temperature must be in K when using this formula. (16)𝑉1 300 = (40) 12 𝑉1 𝑇2 T2 = 375K = 102 οC

3 NJC SH2 Prelim 9476/1/26 [Turn over 3 A mixture of the three gases, oxygen, nitrogen and argon, is at a total pressure of 500 kPa. There is a total of 1.2 moles of gases in the mixture. If the oxygen gas alone occupied the entire volume of the mixture, it would exert a pressure of 150 kPa. At room conditions, the amount of nitrogen gas in the mixture would occupy a volume of 5.76 dm3. Using the data from above, what is the partial pressure of the argon gas in the mixture? A 150 kPa B 200 kPa C 250 kPa D 300 kPa Ans: C Mol ratio of O2 = 150 500 =0.3 Hence amt of O2 = 0.3 x 1.2 = 0.36 mol Amt of N2 = 5.76 24 =0.24 mol Hence amt of Ar = 1.2 – 0.36 – 0.24 =0.6 mol Thus pAr = 0.6 1.2 × 500 = 250 kPa

4 NJC SH2 Prelim 9476/1/26 4 The following graphs were obtained for three gases for the variation of pV with p, where p is the pressure and V is the volume of the gas. Which row is correct if gas M is HCl at 300 K? gas N temperature / K A HCl 400 B CH4 400 C O2 300 D HF 300 Ans: D Recall that real gases would deviate from ideal behaviour at high pressures and low temperatures. Real gas tends towards ideal gas behaviour when the intermolecular forces are negligible and the volume of the gas particles is negligible to the volume of the vessel. Option Explanation A Fo the same gas, it will deviate less at higher temperature since the molecules have more kinetic energy to overcome the intermolecular permanent dipole -permanent dipole (pd-pd) interactions. B CH4 is a non -polar molecule with only weak intermolecular instantaneous dipole induced dipole (id -id). CH 4 will also deviate less at higher temperature since the molecules have more kinetic energy to overcome the intermolecular forces. C O2 is a non-polar molecule with only weak intermolecular id-id, hence should deviate less from ideal behaviour than HCl. D HF is a polar molecule with stronger intermolecular hydrogen bonding interactions than the intermolecular pd-pd of HCl. Hence HF deviates more from ideal behaviour than HCl at the same temperature of 300 K. pV p Ideal gas Gas M Gas N

5 NJC SH2 Prelim 9476/1/26 [Turn over 5 Which element has the same number of electron pairs and unpaired electrons in its valence shell? A beryllium B carbon C nitrogen D oxygen Ans: D electron pairs unpaired electrons Be 1s² 2s² 1 0 C 1s² 2s² 2p² 1 2 N 1s² 2s² 2p³ 1 3 O 1s² 2s² 2p⁴ 2 2 6 The table identifies the shape and polarity of four molecules. Which row is correct? molecule molecular shape polarity A BrF3 Trigonal planar polar B PCl3 trigonal pyramidal polar C SCl2 linear non-polar D CHF3 tetrahedral non-polar Ans: B molecule molecular shape polarity A BrF3 Trigonal planar Non-polar B PCl3 trigonal pyramidal polar C SCl2 bent polar D CHF3 tetrahedral polar

6 NJC SH2 Prelim 9476/1/26 7 Which option about the structure below is correct? Number of sp hybridised C Number of sp2 hybridised C Number of sp3 hybridised C A 1 3 8 B 1 3 6 C 0 4 8 D 0 4 6 Ans: A Refer to diagram below (* represents sp2 C while · represents sp3 C). There are one sp C, three sp2 C and eight sp3 C. 8 Which pair of elements have bonds of the same type between their atoms in their standard states? A aluminium and phosphorus B chlorine and argon C magnesium and silicon D sulfur and chlorine Ans: D A: different • Al: metallic bonds between cations and sea of delocalized electrons • P: weak idid between P ₄ molecules, strong covalent bonds between atoms within the molecule

7 NJC SH2 Prelim 9476/1/26 [Turn over B: different • Cl: weak idid between Cl ₂ molecules, strong covalent bonds between atoms within the molecule • Ar: weak idid between individual atoms C: different • Mg: strong metallic bonds between cations and sea of delocalized electrons • Si: strong covalent bonds between Si atoms (giant covalent lattice) D: same • S: weak idid between S8 molecules, strong covalent bonds between atoms within the molecule • Cl: weak idid between Cl ₂ molecules, strong covalent bonds between atoms within the molecule 9 When 25 cm3 of 1.0 mol dm–3 sodium hydroxide was neutralised with an equal volume of 0.5 mol dm–3 sulfuric acid, the temperature of the mixture rose by 7.0 °C. What would be the temperature change if 50 cm3 of 0.5 mol dm–3 sodium hydroxide is neutralised with an equal volume of 0.25 mol dm–3 sulfuric acid? (Assume negligible heat loss in each case.) A 14.0 °C B 7.0 °C C 3.5 °C D 1.8 °C Ans: C Both H2SO4 and NaOH are strong acid and strong base, fully dissociated in water to give H+ and OH‒ respectively. Reaction is between H+ and OH‒ ions: H+ + OH‒ → H2O Expt 1: Amt of OH‒ = 251000 × 1.0 = 0.025 mol Amt of H+ = 251000 × 0.5 × 2 = 0.025 mol = Amt of H2O formed Expt 2: Amt of OH‒ = 501000 × 0.5 = 0.025 mol Amt of H+ = 251000 × 0.25 × 2 = 0.025 mol = Amt of H2O formed