NJC 2024 Time Practice 2 Answer Booklet

1 NJC SH2 Timed Practice 9729/01/24 [Turn over NATIONAL JUNIOR COLLEGE SH2 TIMED PRACTICE Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 9729/01 27 June 2024 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. Example: Student Examples of Registration No. Shade: 2305648 35648 This document consists of 12 printed pages.

2 NJC SH2 Timed Practice 9729/01/24 1 2 3 4 6 7 8 9 10 A C A D B C D A D 11 12 13 14 15 16 17 18 19 20 B B D B C C C C A B 21 22 23 25 27 28 29 30 D C C C D D B D 1 Which statement about one mole of a metal is always correct? A It contains the same number of atoms as 0.5 mol of hydrogen gas. B It contains the same number of atoms as 1 12 mol of 12C. C It has the same mass as 1 mol of hydrogen atoms. D It can be oxidized by a reaction with an acid. Ans: A Option A is correct 1 mol of M = 6.02 × 1023 atom ½ mol of H2 = 1 mol of H atom = 6.02 × 1023 atom Option B is wrong 1 mol of M = 6.02 × 1023 atom 1 12 mol of 12C = 1 12 × 6.02 × 1023 Option C is wrong Mass of 1 mol of H atom = 1 g Mass of 1 mol of M = 1 × Ar of metal Option D is wrong Not all metal can be oxidized by an acid (H+) Cu2+ + 2e Cu E = +0.34V 2H+ + 2e H2 E = 0.00V Eꝋcell = Eꝋ[R] – Eꝋ[O] Eꝋcell = Eꝋ(H+/H2)– Eꝋ(Cu2+/Cu) = 0.00 – (+0.34) = – 0.34 V Reaction between H+ and Cu is not feasible.

3 NJC SH2 Timed Practice 9729/01/24 [Turn over 2 10 cm3 of a gaseous hydrocarbon was reacted with an excess of oxygen. A contraction of 30 cm3 occurred. On treating the cooled resulting mixture with excess barium hydroxide, a further contraction of 40 cm3 occurred. All volumes were measured at room temperature and pressure. What is the formula of the hydrocarbon? A C2H4 B C2H6 C C4H8 D C4H10 Ans: C CxHy(g) + (x + y 4) O2(g) ⎯→ x CO2(g) + y 2 H2O(l) Reacting vol / cm3 10 60 40 Mole ratio 1 6 4 Ba(OH)2 reacts with acidic gas CO2. Vol of CO2 = 40 cm3 (from 2nd contraction)  x = 4, Initial vol – Final vol = 30 cm3 (1st contraction) (Vol of hydrocarbon + Total Vol of O2) – (Vol of unreacted O2 + Vol of CO2) = 30 cm3 (10 + Total vol of O2) – (Vol of unreacted O2 + 40) = 30 cm3 Total vol of O2 − Vol of unreacted O2 = 60 cm3 Vol of O2 reacted = 60 cm3 x + y 4 = 6 4 + y 4 = 6  y = 8 The molecular formula of the hydrocarbon is C4H8. 3 The following reaction occurs when chlorine is added to water. Cl2(g) + H2O(l) HOCl(aq) + HCl(aq) Which statement about this reaction is correct? A Chlorine is both oxidised and reduced. B Chlorine is oxidised but not reduced. C Hydrgen is both oxidised and reduced. D Hydrogen is oxidised but not reduced. Ans: A Cl2(g) to HOCl (aq) (0) (+1) : oxidation Cl2(g) to Cl–(aq) (0) (-1) : reduction

4 NJC SH2 Timed Practice 9729/01/24 4 X is either nitrogen or sulfur and forms pollutant oxide Y in a car engine. Further oxidation of Y to Z occurs in the atmosphere. In this further oxidation, 1 mol of Y reacts with 0.5 mol of gaseous oxygen molecules. Which statements about X, Y and Z can be correct? 1 The oxidation number of X increases by two from Y to Z. 2 Y has an unpaired electron in its molecules. 3 Y is a polar molecule. A 1 only B 1 and 2 C 2 and 3 D 1, 2 and 3 Ans: D Y can be: NO + 1 2O2 → NO2 (O.N. of N increases from +2 to +4) or SO2 + 1 2O2 → SO3 (O.N. of S increases from +4 to +6) Statement 1 is correct. Statement 2 is correct for NO Both are polar molecule with net dipole moment. Statement 3 is correct

5 NJC SH2 Timed Practice 9729/01/24 [Turn over 6 Histidine is an amino acid. Histidine What are the approximate bond angles 1, 2 and 3? 1 2 3 A 109.5° 107° 90° B 120° 107° 109.5° C 120° 120° 90° D 120° 120° 109.5° Angle 1: 3 bond pairs (120°) Angle 2: 3 bond pairs + 1 lone pair (107°) Angle 3: 4 bond pairs (109.5°) 7 Ammonium ions, NH4+, are formed when ammonia gas reacts with hydrogen chloride gas. Which statement about the changes that occurs in this reaction is correct? A The dipole moment of an ammonium ion is greater than the dipole moment of an ammonia molecule. B The H−N−H bond angle decreases when an ammonium ion is formed. C The hybridisation of nitrogen does not change. D There is electron transfer from nitrogen to chlorine. Ans: C NH3 + HCl → NH4+ + Cl- Option A is wrong. There is no dipole moment in an ion as they are charged particles. Option B is wrong. The H -N-H bond angles increases from 107° (trigonal pyramidal) to 109.5° (tetrahedral). Option C is correct. The hybridisation of nitrogen remains as sp 3 with 4 electron regions around N. Option D is wrong. There is no change in oxidation number in the reaction.

6 NJC SH2 Timed Practice 9729/01/24 8 Ethylene glycol, HOCH 2CH2OH, is used as a de -icer. It allows ice to melt at temperatures below 0 °C. Which statements are correct? 1 Ethylene glycol changes the extensive network of hydrogen bonds in ice. 2 Ethylene glycol molecules form hydrogen bonds with other ethylene glycol molecules. 3 Ethylene glycol molecules will dissolve in the water formed from the ice. A 1 only B 1 and 2 C 2 and 3 D 1, 2 and 3 Ans: D Statement 1 is correct. Ethylene glycol molecules form hydrogen bonds with H2O molecule and changes the extensive network of hydrogen bond in ice. Statement 2 is correct. Ethylene glycol molecule form hydrogen bonds with other ethylene glycol molecule. Statement 3 is correct. Ethylene glycol molecules form significant hydrogen bonds with water molecule which will make it soluble in water.

7 NJC SH2 Timed Practice 9729/01/24 [Turn over 9 When an evacuated tube of volume 400 cm 3 is filled with gas at 300 K and 101 kPa, the mass of the tube increases by 0.65 g. Assume the gas behaves as an ideal gas. What is the identity of the gas? A Argon B Helium C Krypton D Neon Ans: A pV = nRT (101 × 103)(400 × 10-6) = ( 0.65 𝑀𝑟 )(8.31)(300) Mr = 40 10 Two identical bulbs at the same temperature contain ideal gases A and B separately. The density of gas A is twice that of gas B and the molecular mass of gas A is half that of gas B. What is the ratio of the pressure of gas A to that of gas B? A 1 : 2 B 1 : 1 C 2 : 1 D 4 : 1