2024 Prelims NJC H2 Chem P1 (QP)

NJC/H2 Chem Preliminary Examination/01/2024 [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 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 13 printed pages and 3 blank page.

2 NJC/H2 Chem Preliminary Examination/01/2024 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 2 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 3 When iodine is oxidized by nitric acid, a white crystalline solid oxide can be isolated from the mixture. 0.001 mole of this oxide reacts with 0.01 mole of acidified potassium iodide to give 0.006 mole of iodine, I2. What is the oxidation number of iodine in the oxide? A +1 B +5 C +6 D +10 4 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 IF3, H2O C HCN, SO3 D CO2, NCl3

3 NJC/H2 Chem Preliminary Examination/01/2024 [Turn over 5 Hydrogen peroxide solution decomposes. The equation for this reaction is shown. 2H2O2(aq) 2H2O(l) + O2(g) A 300 cm3 sample of hydrogen peroxide solution is warmed. After 150 minutes, 10.00 dm 3 of oxygen gas, measured at r.t.p., is collected. Under these conditions, the reaction has a constant half-life of 50 minutes. What is the initial concentration of the hydrogen peroxide solution? A 0.79 mol dm−3 B 1.6 mol dm−3 C 2.8 mol dm−3 D 3.2 mol dm−3 6 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 7 X and Y react together to form Z in a reversible reaction. The equilibrium yield of Z at different conditions are shown in the following table. Conditions Equilibrium yield of Z High Temperature Decreased High Pressure Increased Which equation could represent this reaction? A X(g) + Y(g) ⇌ Z(g) ∆H = –100 kJ mol-1 B X(g) + Y(g) ⇌ Z(g) ∆H = +100 kJ mol-1 C X(s) + Y(g) ⇌ 2Z(g) ∆H = –100 kJ mol-1 D X(s) + Y(g) ⇌ 2Z(g) ∆H = +100 kJ mol-1

4 NJC/H2 Chem Preliminary Examination/01/2024 8 PCl5 decomposes as shown. PCl5(g) PCl3(g) + Cl2(g) 1.0 mole of PCl5(g), 1.0 mole of PCl3(g) and 1.0 mole of Cl2(g) are placed in a container of volume 2 dm3 at 250 °C and allowed to reach equilibrium. At this temperature, the equilibrium mixture contains 1.8 moles of PCl3. What is the value of Kc at 250 oC? A 0.12 B 1.8 C 8.1 D 16.2 9 Ammonium carbonate is a crystalline solid. On gentle warming a reaction occurs, forming ammonia as one product. How are the carbonate ions behaving during this reaction? A Brønsted-Lowry acid B Brønsted-Lowry base C oxidising agent D reducing agent 10 The dissociation constant, Kw, for the ionisation of water, H 2O H+ + OH –, at different temperatures is given below. Temperature / oC Kw / mol2 dm-6 0 25 50 1.15 x 10–15 1.00 x 10–14 5.50 x 10–14 Which statement is correct? A Only at 25 oC are [H+] and [OH–] equal. B The equilibrium lies furthest to the right at 0 oC. C The forward reaction is exothermic. D The pH of water decreases with temperature.

5 NJC/H2 Chem Preliminary Examination/01/2024 [Turn over 11 The indicator bromophenol blue, HIn, changes colour from yellow to blue over a pH range of 3.0 to 4.6. Which statements are correct? 1 When bromophenol blue is added to water at 25 oC, [HIn] < [In–]. 2 Bromophenol blue would be a suitable indicator for the titration of a strong base and a weak acid. 3 The In– ions are yellow. A 1,2 and 3 B 1 and 3 only C 1 only D 2 and 3 only 12 Phosphoric acid is a tribasic acid. H3PO4 H2PO4− + H+ H2PO4− HPO42− + H+ HPO42− PO43− + H+ The graph shows the fraction of each species at different pH. What is the numerical value of Ka2? A 2.0  10−10 B 7.9  10−8 C 2.0  10−5 D 6.3  10−3 0.0 0.2 0.4 0.6 0.8 1.0 0 2 4 6 8 10 12 14 Ka1 Ka2 Ka3 3 pH H2PO4− H3PO4 HPO42− PO43− Fraction of species 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

6 NJC/H2 Chem Preliminary Examination/01/2024 13 An acidified solution contains 0.10 mol dm –3 of ZnSO 4 and 0.10 mol dm –3 of CuSO 4. Hydrogen sulfide gas, H 2S, is bubbled through the solution until it is saturated with H 2S at 15 oC. The concentration of S2–(aq) in the solution reaches 1×10–35 mol dm–3. The solubility product of ZnS at 15 oC is 1×10 –24 mol2 dm–6 and that of CuS is 1×10–40 mol2 dm–6. Which statement is correct? A No precipitate is formed. B ZnS only is precipitated. C CuS only is precipitated. D Both ZnS and CuS are precipitated. 14 In this question the symbol ‘<’ means ‘less positive than’ or ‘more negative than’. Silver chloride dissolves in dilute NH3(aq) whereas silver bromide is only soluble in concentrated NH3. The following equations represent the equilibria involved. AgCl(s) AgCl (aq) ∆G1 AgCl(aq) + 2NH3(aq) Ag(NH3)2Cl(aq) ∆G2 AgBr(s) AgBr(aq) ∆G3 AgBr(aq) + 2NH3(aq) Ag(NH3)2Br(aq) ∆G4 Some relationship between the free energies of these four reactions are as follows. 1 (∆G1 + ∆G2) < (∆G3 + ∆G4) 2 ∆G2 = ∆G4 3 ∆G2 < ∆G4 4 ∆G1 < ∆G3 Which relationships are correct?