NJC 2024 H1 Chem Prelim P1 Ans

NJC/H1 Chem Preliminary Examination/01/2024 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 1 Multiple Choice Additional Materials: Optical Answer Sheet Data Booklet 8873/01 19 September 2024 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: 2305648 35648 This document consists of 15 printed pages and 1 blank page.

2 NJC/H1 Chem Preliminary Examination/01/2024 Suggestion solution for P1 (MCQ) 1 C 11 C 21 D 2 B 12 A 22 C 3 C 13 C 23 B 4 B 14 B 24 A 5 A 15 D 25 B 6 D 16 C 26 A 7 B 17 C 27 A 8 A 18 C 28 D 9 A 19 D 29 B 10 B 20 A 30 D

3 NJC/H1 Chem Preliminary Examination/01/2024 [Turn over 1 Use of the Data Booklet is relevant to this question. A sample of 35.6 g of hydrated sodium carbonate contains 25.84% sodium ions by mass. When this sample is heated, anhydrous sodium carbonate and water vapour are formed. What is the mass lost? A 7.2 g B 10.6 g C 14.4 g D 21.2 g Ans: C Na2CO3.xH2O → Na2CO3 + xH2O 46 106 + 18(𝑥) × 100% = 25.84 x = 4 Mass of water given off = 35.6 178 × 18 × 4 = 14.4g 2 Diamond is an allotrope of carbon. The mass of a diamond can be measured in carats. One carat is 0.200 g of carbon. Which expression gives the number of carats that contain 6.02 × 1023 carbon atoms? A 0.200 × 12.0 B 12.0 0.200 C 0.200 12.0 D 0.200 6.02 × 1023 × 12.0 Ans : B 1 mol of C contains 6.02 × 1023 C atoms Mass of C = 12.0 g Number of carat = 12.0 0.200

4 NJC/H1 Chem Preliminary Examination/01/2024 3 One of the main chemicals in air bags in cars is the ionic compound sodium azide, NaN3. When the car is in a violent head-on impact, a sensor causes ignition of the sodium azide to form nitrogen gas explosively, rapidly filling the air bag. I 2NaN3 → 2Na + 3N2 Fine particles of potassium nitrate and silicon dioxide are also present to react with the metallic sodium. II 2KNO3 + 10 Na → 5Na2O + K2O + N2 III K2O + SiO2 → K2SiO3 IV Na2O + SiO2 → Na2SiO3 Which statement is not correct? A Equations III and IV represent acid-base reactions. B In reaction I, sodium ions are reduced. C In reaction II, both sodium atoms and potassium ions are oxidised. D In reaction II, potassium nitrate is an oxidising agent. Ans : C Option A is correct. For reactions III and IV, basic oxide (metal oxide) reacts with acidic oxide (non-metal) oxide to produce salts. Option B is correct. Oxidation state of Na decreases from +1 (in NaN3) to 0 (in Na). Option C is incorrect. K+ ion is not oxidised, its oxidation state remains the same at +1. Option D is correct. KNO3 is an oxidising agent that oxidises Na to Na+.

5 NJC/H1 Chem Preliminary Examination/01/2024 [Turn over 4 When iodine is oxidized by nitric acid, a white crystalline solid oxide can be isolated from the mixture. 1 mol of this iodine oxide reacts with 10 mol of acidified potassium iodide to give 6 mol of I2. What is the oxidation number of iodine in the oxide? A +1 B +5 C +6 D +10 Ans: B 1 mol of iodine oxide reacts with 10 mol of I − to gives 6 mol of I 2. Balancing number of I atoms on both sides, 6 mol of I 2 contains 12 mol of I atoms. Hence, 1 mol of iodine oxide contains 2 mol of iodine atoms. 2 mol Ix+ reacts with 10 mol I− to produce 6 mol I2. [O] 2I− ⎯→ I2 + 2e− 10 mol I− gives 10 mol of e− [R] Ix+ + ne− ⎯→ I2 2 mol of Ix+ gains 10 mol of e− 1 mol of Ix+ gains 5 mol of e− to give I2 During reduction, oxidation state of Ix+ decreases by 5 units from +5 to 0. 5 Use of the Data Booklet is relevant to this question. Sodium and fluorine are both reactive elements. Which statements are correct? 1 One Na atom has two more protons than one F− ion. 2 One Na atom has two more neutrons than one F atom. 3 One Na+ ion has the same number of electrons as one F− ion. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Ans: A F → F- Na → Na+ p 9 9 11 11 n 10 10 12 12 e 9 10 11 10

6 NJC/H1 Chem Preliminary Examination/01/2024 7 Which statements about the structure of the AlCl3 molecule are correct? 1 The aluminium atom has an unfilled octet. 2 The molecule is planar in shape. 3 In the molten state, it consists of Al3+ and Cl− ions. A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Ans : B Statement 3 is wrong. AlCl3 is a covalent molecule, it does not exist as ions in molten state. Statements 1 and 2 are correct. Shape around Al is trigonal planar (3b.p, 0l.p) and also Al to have an unfilled octet (only 6 electrons after bonding). 6 Which pair of compounds meets the criteria below? • The first compound has a larger bond angle than the second compound. • The second compound is more polar than the first compound. A CO2, BCl3 B SF6, H2O C HCN, SO3 D CO2, NH3 Ans: D molecules bp lp shape angle Polar? CO2 2 0 Linear 180o Non polar BCl3 3 0 Trigonal planar 120 o Non polar SF6 6 0 Octahedral 90o Non-polar H2O 2 2 Bent 105o Polar HCN 2 0 Linear 180o Polar SO3 3 0 Trigonal Planar 120o Non polar NH3 3 1 Trigonal pyramidal 107.5o Polar

7 NJC/H1 Chem Preliminary Examination/01/2024 [Turn over 8 Consider the following four compounds. 1 (CH3)3CH 2 CH3CH2CH2CH3 3 CH3CH2CH2OH 4 CH3CH2Cl What is the order of increasing boiling point of the compounds? A 1 2 4 3 B 2 1 4 3 C 3 4 2 1 D 4 3 2 1 Ans : A 1. (CH3)3CH: branched(spherical) → weaker idid than 2 → lowest b pt. 2. CH3CH2CH2CH3: straight chain → stronger idid than 1. 3. CH3CH2CH2OH: H–bonding → highest b pt. 4. CH3CH2Cl : pd–pd 9 The diagram below represents the energy changes associated with NaHCO3 and H2SO4. ∆H / kJ mol─1 NaHCO3(s) + aq → NaHCO3(aq) + 15.0 2NaHCO3(s) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g) + 37.0 Determine the value of ∆H1. A + 7.0 kJ mol−1 B + 22.0 kJ mol−1 C + 37.0 kJ mol−1 D +52.0 kJ mol−1 Ans : A ∆H1 = −2  15 + 37 = +7.0 kJ mol−1 ∆H1

8 NJC/H1 Chem Preliminary Examination/01/2024 10 In order to determine the enthalpy of neutralisation of a strong acid and a strong alkali, 25.0 cm 3 of 2.00 mol dm −3 sodium hydroxide is added to 25.0 cm 3 of 2.00 mol dm −3 hydrochloric acid. The increase in temperature is 12°C. In a second experiment, the same method is used, but 50.0 cm 3 of 2.00 mol dm −3 sodium hydroxide is added to 50.0 cm3 of 2.00 mol dm−3 hydrochloric acid. What is the increase in temperature in the second experiment? A 6°C B 12°C C 24°C D 48°C Ans