2024 TJC Prelims H1 P1 QP & Ans

1 8873 / TJC Prelims / 2024 TEMASEK JUNIOR COLLEGE 2024 JC2 PRELIMINARY EXAMINATION Higher 1 CHEMISTRY 8873/01 Paper 1 Multiple Choice 12 September 2024 1 hour Additional Materials: Multiple Choice Answer Sheet (OMS) Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. There are thirty questions In this paper. Answer all questions. For each question there are four possible answers A, B, C, 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. Write your name & Civics Group on the Answer sheet. Shade your index number in the appropriate boxes. 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. This document consists of 12 printed pages. Write your name and Civics Group Index number (refer to entry proof)

2 8873 / TJC Prelims / 2024 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 (OMS). 1 Which statement about the electrons in a ground state nitrogen atom is correct? A There are more electrons in s orbitals than there are in p orbitals. B Electrons are present in two different energy levels. C There is a pair of electrons in one of the p orbitals. D The occupied orbital of highest energy is spherical. Answer: A The electronic configuration of N is 1s22s22p3. A: Correct statement. There are 4 electrons in s orbitals and 3 electrons in p orbitals. B: Electrons are present in three different energy levels (1s, 2s and 2p). C: All the electrons in p orbitals are unpaired. D: The occupied orbital of highest energy level is 2p, which has a dumb-bell shape. 2 In an experiment, protons are deflected by an angle of +10°. In another experiment under identical conditions, particle X is deflected by an angle of –2.5°. What could be the composition of particle X? protons neutrons electrons A 4 4 5 B 2 2 3 C 2 2 1 D 1 2 2 Answer: B The angle of deflection is  charge/ mass. Since X is deflection in the opposite direction as proton, it has a negative charge, with charge/mass = ¼. charge mass Charge/ mass A -1 8 -1/8 B -1 4 -1/4 C +1 4 +1/4 D -1 3 -1/3

3 8873 / TJC Prelims / 2024 [Turn over 3 Which compound is composed of cation and anion that has the same number of electrons as each other? 1 Na2O 2 NaN3 3 NH4F 4 NaCl A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4 Answer: A Cation Number of e- Anion Number of e- 1 Na+ 11 – 1 = 10 O2- 8 + 2 = 10 2 Na+ 10 N3- 3(7) + 1 = 22 3 NH4+ 7 + 4 – 1 = 10 F- 9 + 1 = 10 4 Na+ 10 Cl- 17 + 1 = 18 4 Use of the Data Booklet is relevant to this question. The sixth ionisation energies of four different elements are shown below. The elements are arsenic, selenium, antimony and tellurium (though not necessarily in that order) from Groups 15 and 16. Which of the following shows the sixth ionisation energy of antimony? A 12300 B 10400 C 7880 D 6820 Answer: B Arsenic (As) and Antimony (Sb) are in Group 15 and have 5 valence electrons in their valence shell. The sixth ionisation energies of As and Sb involve the removal of electron from an inner electron shell, hence the values are large → options A and B. Sb is in a Period below As, the electron to be removed from Sb is further from the nucleus and hence less strongly attracted. Hence, the sixth ionisation energy indicated in B is for Sb.

4 8873 / TJC Prelims / 2024 5 Which feature is present in each of the ions CO32– and SO32–? A All bond angles are 120° B One dative covalent bond C Three sigma bonds D Eight lone pairs of electrons Answer: C , 6 Beryllium chloride, BeCl2, fully reacts with ammonia, NH3 to form a compound. Which of the statements is incorrect? A The compound is formed from 1 mole of BeCl2 and 2 moles of NH3. B The Be-N bond formed is chemically similar to a covalent bond. C The beryllium atom in beryllium chloride is electron deficient. D The compound is capable of forming only two hydrogen bonds per molecule. Answer: D A & C Only 4 e around Be on BeCl 2, hence electron deficient. It can accommodate another 2 pairs of e from N to achieve octet. B A dative bond is the same as a single covalent bond (strength and length) D The compound formed has no more lone pairs of e on N available for hydrogen bonding. 7 In which of the following pairs of compounds would the first compound have a higher melting point than the second compound? 1 Na2O, K2O 2 AlF3, AlCl3 3 MgO, MgCl2

5 8873 / TJC Prelims / 2024 [Turn over A 1, 2 and 3 B 1 and 2 C 2 and 3 D 1 only Answer: A Option 1: Correct. 2 2 MO MO LE qq rr +− +−  + . As K Narr++ , Na2O has a higher melting point. Option 2: Correct: AlF3 is ionic while A lCl3 is simple covalent  AlF3 has a higher melting point. Option 3: Correct: +− +−  + 22 22 MO MO LE qq rr & +− +−  + 2 2 M M LE Cl Cl qq rr . As −−2O Clqq & −− 2Cl Orr , MgO has a higher melting point than MgCl2. 8 Trimethoprim (TMP) is used for the treatment of urinary tract infections. It has the following structure: Which are the correct bond angles w, x, y and z? w x y z A 90 180 120 90 B 90 105 118 107 C 109.5 105 120 107 D 109.5 180 118 120 Answer: C w: 4 bond pairs 0 lone pair (tetrahedral) x: 2 bond pairs 2 lone pairs (bent) y: 3 bond pairs 0 lone pair (trigonal planar) z: 3 bond pairs 1 lone pair (trigonal pyramidal

6 8873 / TJC Prelims / 2024 9 Use of the Data Booklet is relevant to this question. A solution containing 25 cm3 of 0.1 mol dm-3 VO2+ reacts completely with 0.245 g of zinc. Which of the following can be the vanadium-containing species in the product? A VO3– B VO2+ C V3+ D V2+ Answer: D Number of moles of VO2+ = 325 0.1 2.5 10 mol1000 − =  Number of moles of Zn = 30.245 3.75 10 mol65.4 −= Zn → Zn2+ + 2e 2VO2+  3Zn  6 e– VO2+  3 e– Oxidation state of V in product = +2, hence V2+ is formed. 10 Which oxide does not react with dilute sodium hydroxide to produce a salt? A Al2O3 B P4O10 C SO2 D SiO2 Answer: D oxide nature of oxide reacts with dil. NaOH remarks Al2O3 amphoteric yes – P4O10 acidic yes – SO2 acidic yes – SiO2 acidic no only reacts with hot and concentrated strong alkalis to form silicates 11 When phosphoryl chloride, POCl3, dissolves in water, it gives a mixture of phosphoric acid and hydrochloric acid. How many moles of sodium hydroxide would be needed to neutralise the solution formed by adding one mole of POCl3 to excess water? A 3 B 4 C 5 D 6

7 8873 / TJC Prelims / 2024 [Turn over Answer: D POCl3 + 3H2O → H3PO4 + 3HCl H3PO4 is a tribasic acid and 3 mol of NaOH is needed to neutralise 1 mol of H3PO4. 1 mol of NaOH is needed to neutralise 1 mol of HCl. Hence, in total, 6 mol of NaOH is needed. 12 The graph below shows the variation in the second ionisation energies for the consecutive elements Q to Z in the Periodic Table, all with proton number below 20 What can be deduced from the above? 1 T has a smaller atomic radius than U. 2 Effervescence is observed when a magnesium strip is dipped into the aqueous solution containing the chloride of element W. 3 When the oxide of U is mixed with water, an alkaline solution is formed. A 1, 2 and 3 B 1 and 2 C 2 and 3 D 3 only Answer: C 2nd I.E. means that the 2 nd electron is removed. The big drop in 2 nd I.E. from T to U means that 2nd electron in T is removed from an inner electron shell. T has 1 v