NJC 2025 H2 Chemistry Prelim P1 QP

NJC/H2 Chem Prelim/01/2025 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 9729/01 23 September 2025 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, 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. 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. Example: Student Examples of Registration No. Shade: 2405648 45648 This document consists of 12 printed pages.

2 NJC/H2 Chem Prelim/01/2025 1 Sodium chromate(VI), Na2CrO4, is manufactured by heating chromite, FeCr2O4, with sodium carbonate in an oxidising atmosphere. Chromite contains Cr2O42– ions. 4FeCr2O4 + 8Na2CO3 + 7O2 ⎯→ 8Na2CrO4 + 2Fe2O3 + 8CO2 What happens in this reaction? A Chromium and iron are the only elements oxidised. B Chromium, iron and carbon are oxidised. C Only chromium is oxidised. D Only iron is oxidised. 2 Which species has two unpaired electrons? A B+ B Cu+ C Mg D S 3 The variation in the second ionisation energy of eight consecutive elements in the Periodic Table with atomic numbers ≤ 20 is shown in the graph. Which element is a Group 13 element?

3 NJC/H2 Chem Prelim/01/2025 [Turn over 4 What do the ions 15N3− and 14C4− have in common? A They have 10 neutrons in their nuclei. B They have more electrons than neutrons. C They have a valence electronic configuration of 3s2 3p6. D They contain the same number of nucleons in their nuclei. 5 What is the order of decreasing enthalpy change for the three reactions shown? Rb+(g) ⎯→ Rb2+(g) + e− ∆H1 Br−(g) ⎯→ Br(g) + e− ∆H2 Kr(g) ⎯→ Kr+(g) + e− ∆H3 A ∆H1 > ∆H2 > ∆H3 B ∆H1 > ∆H3 > ∆H2 C ∆H2 > ∆H1 > ∆H3 D ∆H2 > ∆H3 > ∆H1 6 Barium dithionate, BaS2O6•2H2O, is soluble in water. S2O62– ions slowly decompose in acidic solution. S2O62–(aq) ⎯→ SO2(g) + SO42–(aq) 3.513 g of BaS2O6•2H2O is dissolved in some water and the solution made up to the mark with HCl(aq) in a 100 cm3 volumetric flask. At time x min, a white precipitate of mass 0.661 g is present in the flask. What is the concentration of BaS2O6 in the volumetric flask at time x min? [Ar: Ba, 137.3; S, 32.1; O, 16.0; H, 1.0] A 0.0077 mol dm–3 B 0.0090 mol dm–3 C 0.077 mol dm–3 D 0.090 mol dm–3

4 NJC/H2 Chem Prelim/01/2025 7 NH4Fe(SO4)2•12H2O is a hydrated ‘double salt’. A student analyses this double salt using the following chemical tests. Which row gives the correct result for the stated test? Test Results 1 Reaction with cold NaOH(aq) Green ppt 2 Reaction with Ba(NO3)2(aq) White ppt 3 Reaction with warm NaOH(aq) Red-brown ppt and an alkaline gas A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 8 Which statements about BF3 and NF3 are correct? 1 The shape of BF3 is trigonal planar while that of NF3 is trigonal pyramidal. 2 Both BF3 and NF3 are polar molecules. 3 BF3 can act as a Lewis acid because the boron atom has empty low -lying orbitals. A 1 and 2 B 2 and 3 C 1 and 3 D 1, 2 and 3 9 Silicon carbide has a similar structure to diamond. Silicon carbide can be used as A a lubricant. B a tip for cutting tools. C a substitute for pencil ‘lead’. D an electrical conductor. 10 Which statement is not a basic assumption of the kinetic theory of gases? A The atoms or molecules have negligible size in comparison with the space they occupy. B There are negligible intermolecular forces between the gas particles. C Collisions between the individual particles and the vessel are perfectly elastic. D The particles of a given gas have the same kinetic energy at a given temperature.

5 NJC/H2 Chem Prelim/01/2025 [Turn over 11 The diagram below shows two containers of argon gas connected by a closed tap. Each container has a volume of 500 dm3. The temperature of the system is changed to 250 °C and the tap is opened. What is the pressure of argon within the system at 250 °C? A 7.29 kPa B 14.6 kPa C 15.3 kPa D 30.5 kPa 12 The standard enthalpy change of combustion of but-1-ene, CH2=CHCH2CH3(g), is x kJ mol−1. The standard enthalpy change of the reaction 2C2H4(g) ⎯→ CH2=CHCH2CH3(g) is y kJ mol−1. What is the standard enthalpy change of combustion of ethene, C2H4(g)? A 𝑥 2 + y kJ mol−1 B x + 𝑦 2 kJ mol−1 C 𝑥 + 𝑦 2 kJ mol−1 D 𝑥 𝑦 2 kJ mol−1

6 NJC/H2 Chem Prelim/01/2025 13 Which suggested mechanism is consistent with the experimentally-obtained rate equation? rate equation suggested mechanism A rate = k[N2O][H2] 2NO + H2 ⎯→ N2O + H2O N2O + H2 ⎯→ N2 + H2O B rate = k[NO]2[H2]2 2NO + H2 ⎯→ N2O + H2O N2O + H2 ⎯→ N2 + H2O C rate = k[H2O2][I−] H2O2 + I− ⎯→ IO−+ H2O H2O2 + IO− ⎯→ I− + H2O + O2 D rate = k[H2O2][IO−] H2O2 + I− ⎯→ IO−+ H2O H2O2 + IO− ⎯→ I− + H2O + O2 14 Propanone reacts with iodine in the presence of sulfuric acid. CH3COCH3 (aq) + I2 (aq) ⎯→ CH3COCH2I (aq) + HI(aq) The rate equation for this reaction is: rate = k[H+][CH3COCH3]. Two experiments were carried out. In both experiments, the initial concentrations of propanone and iodine remained the same but the initial concentration of the sulfuric acid was changed. The initial rate in the first experiment was three times faster than the initial rate in the second experiment. In the first experiment the initial pH was 1.50. What is the initial pH in the second experiment? A 1.02 B 1.98 C 2.28 D 4.50 15 Which factor contributes to Ba(NO3)2 decomposing at a higher temperature than Mg(NO3)2? A The charge density of the Ba2+ ion is lower than that of the Mg2+ ion. B The standard enthalpy change of formation of BaO is more negative than that of MgO. C The lattice energy of Ba(NO3)2 is less negative than that of Mg(NO3)2. D The melting point of Ba(NO3)2 is higher than that of Mg(NO3)2. slow slow slow slow

7 NJC/H2 Chem Prelim/01/2025 [Turn over 16 Which statement explains the trend of decreasing volatility from HCl to HI? A The electronegativity between the bonded atoms increases. B The molecules are polar and they have increasingly stronger permanent dipole - permanent dipoles. C There are more electrons in iodine atom than in chlorine atom. D The bond length decreases from H−Cl to H−I, hence thermal stability increases. 17 The graphs below show the variation of two properties of some Period 3 elements and/or their compounds. Which option correctly describes properties 1 and 2? Property 1 Property 2 A atomic radius of the elements electrical conductivity of the elements B boiling point of the chlorides at the highest oxidation states pH of the oxides when added to water