NJC 2025 H1 Chemistry Prelim P1 Ans

NJC/H1 Chem Preliminary Examination/01/2025 [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 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: 2305648 35648 This document consists of 11 printed pages and 1 blank page.

2 NJC/H1 Chem Preliminary Examination/01/2025 Suggestion solution for P1 (MCQ) 1 A 11 C 21 B 2 D 12 D 22 B 3 C 13 C 23 B 4 C 14 D 24 D 5 B 15 A 25 B 6 C 16 B 26 C 7 C 17 C 27 D 8 A 18 D 28 B 9 D 19 D 29 B 10 B 20 C 30 C

3 NJC/H1 Chem Preliminary Examination/01/2025 [Turn over 1  decay occurs when an atom’s nucleus emits an alpha particle, which is a helium nucleus. The radioactive isotope, Radium 226, undergoes  decay. 88226𝑅𝑎 → 24𝐻𝑒 + X Which row in the table correctly describes the nuclear make-up of X? number of protons number of neutrons A 86 136 B 88 136 C 86 138 D 88 138 Ans: A No. of neutrons of Ra = 226 – 88 = 138 No of protons of X = 88 – 2 = 86 No. of neutrons of X = 138 – 2 = 136 2 Which of the elements have the most number of unpaired electrons? A F B O C Al D P Ans: D Electronic Configurations F: 1s2 2s2 2p5 O: 1s2 2s2 2p4 Al: 1s2 2s2 2p6 3s2 3p1 P: 1s2 2s2 2p6 3s2 3p3

4 NJC/H1 Chem Preliminary Examination/01/2025 3 The successive ionisation energies of element A and B are shown below. ionisation energies / kJ mol‒1 1st 2nd 3rd 4th 5th 6th 7th 8th A 1011 1907 2914 4964 6274 21267 25431 29872 B 1251 2298 3822 5159 6542 9362 11018 33604 What is the formula of the compound formed when A reacts with B? A AB B A2B C AB3 D AB4 Ans: C For A, the largest increase in I.E is from the 5th to 6th I.E => Group 15 For B, the largest increase in I.E is from the 7th to 8th I.E=> Group 17 Hence, AB3 is the answer. 4 Metal chlorates can be prepared by adding chlorine to hot metal hydroxides like KOH: 3 Cl2 + 6 KOH → 5 KCl + KClOx + 3 H2O From the above equation, determine the number x of the O in KClOx. A 1 B 2 C 3 D 4 Ans: C From the equation, 5 C l atoms are reduced from an oxidation number of 0 to −1. The last remaining Cl atom will hence oxidise from 0 to +5. Hence, there are 3 O on KClOx to balance the charge.

5 NJC/H1 Chem Preliminary Examination/01/2025 [Turn over 5 Boron Nitride (BN) has three main crystalline structures, of which the most common is the hexagonal type, featuring a layered structure similar to graphite. Which of the sentences describing the structure is incorrect? A A giant covalent structure with weak intermolecular forces of attraction between layers B A simple covalent structure with weak intermolecular forces of attraction C The B is covalently bonded to 3 other N and vice versa. D The BN bond is polar Ans : B 1. BN has a hexagonal structure similar to graphite and is giant covalent. Hence it has weak IMF between layers 2. As it is structurally similar to graphite, it cannot be simple covalent 3. In graphite, C is covalently bonded to 3 other C. 4. N is more electronegative than B and hence the bond is polar. 6 What is the total number of σ and π bonds in the structure below? σ π A 14 2 B 14 3 C 30 2 D 30 3 Ans: C

6 NJC/H1 Chem Preliminary Examination/01/2025 7 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. Ans: C Decreasing volatility means increasing boiling point / stronger intermolecular forces of attraction. The difference in electronegativity between the H and the halogen decreases from HCl to HI, i.e. HI is the least polar and hence the pd-pd between HI is the weakest. This does not help to explain the trend. Instead, the size of electron cloud increases from HCl to HI, resulting in stronger instantaneous dipole-induced dipole interactions (id-id) which help to explain the trend. The covalent H-X bonds are not broken during boiling, so option D is irrelevant. 8 Which of the species contains the largest bond angle? A ICl2− B SO2 C CH4 D SF6 Ans : A A: 2 bond pair and 3 lone pairs. Hence linear in shape and 180o. B: 2 bond pair and one lone pair. Hence, bent in shape and >120o. C: 4 bond pairs. Hence tetrahedral in shape and 109.5o. D: 6 bond pairs. Hence, octahedral in share and 90o.

7 NJC/H1 Chem Preliminary Examination/01/2025 [Turn over 9 Which of the following does the first compound have a higher melting point than the second compound. 1 Na2O, HCl 2 AlCl3, CaCl2 3 CH3CH2OH, CH2(OH)CH2(OH) A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Ans: D 1. Na2O has a giant ionic lattice while HCl has a simple covalent structure. 2. AlCl3 is simple covalent structure while is giant ionic lattice lattice. 3. CH2(OH)CH2(OH) has more extensive hydrogen bonding than CH3CH2OH 10 Which of the reactions is the first reactant acting as a Bronsted-Lowry Acid? 1 H2O + NH3 ⇌ OH− + NH4+ 2 HCl + CH3NH2 → CH3NH3+Cl− 3 CH3CHOOH + HCl → CH3CHOOH2+Cl− A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 1 only Ans: B 1. H2O donates a H+ to NH3 and behaves as a Bronsted-Lowry Acid 2. HCl donates a H+ to CH3NH2 and behaves as a Bronsted-Lowry Acid 3. CH3CHOOH accepts a H+ from HCl and behaves as a Bronsted-Lowry Base 11 The ionic product of water is the product of the concentration of H + and OH − from the dissociation of water, of which is represented by the equation below: H2O H+ + OH– H=+ve The Kw of water is 1.0 x 10−14 mol2 dm 6 at 25oC. Which of the statements correctly describes what happens when the temperature is raised? 1 pH of water decreases 2 [H+] > [OH−] 3 Kw value increases A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 1 only

8 NJC/H1 Chem Preliminary Examination/01/2025 Ans: C 1. [H+] increases as POE shifts right to produce more H+ when temperature is raised. 2. [H+] = [OH−] for pure water 3. As Kw = [H+][OH−], the value increases as more H+ and OH− are dissociated. 12 Which of the following mixtures will form a buffer solution? All the reagents have the same concentration. A 20 cm3 of HNO3 mixed with 20 cm3 of NH3 B 10 cm3 of CH3COOH mixed with 20 cm3 of NaOH C 20 cm3 of HCl mixed with 20 cm3 of NH3 D 5 cm3 of H2SO4 mixed with 15 cm3 of NH3 Ans : D A. Only the sal