NJC 2024 H1 Chem Prelim P2 QP

1 NJC/H1 Chem Preliminary Examination/02/2024 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 17 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your name, registration number and subject class on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer one question. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. A1 /7 A2 /12 A3 /20 A4 /11 A5 /10 Weightage B6 / B7 /20 Paper 1 (33%) /33 Paper 2 /80 Paper 2 (67%) /67 Paper 1 /30 Overall This document consists of 23 printed pages and 1 blank page.

2 NJC/H1 Chem Preliminary Examination/02/2024 Section A Answer all the questions in this section in the spaces provided. 1 The structure of the atom was the subject of much discussion by scientists in the 19th and 20th centuries. The model that is agreed upon today was largely developed by Bohr, Rutherford, Moseley and Chadwick and describes atoms as consisting of smaller particles called protons, neutrons and electrons. (a) (i) Complete the Table 1.1 to show the relative charge, relative mass and behaviour in an electric field of each of these three sub-atomic particles. Table 1.1 proton neutron electron relative charge relative mass Direction of deflection of particle in an electric field [2] (ii) Which particle will be deflected the most in an electric field? ………………………………………………………………………………………… [1] (b) An element has a proton number of 16 and a nucleon number of 33. Draw a detailed diagram to represent the arrangement of protons, neutrons and electrons in an atom of this element. [2]

3 NJC/H1 Chem Preliminary Examination/02/2024 [Turn over (c) The element sulfur has four naturally occurring isotopes as shown in Table 1.2. Table 1.2 isotope relative abundance / % 32S 94.93 33S 0.76 34S 4.29 36S 0.02 Use the relative abundance data to calculate the relative atomic mass of sulfur to 4 significant figures. Show your working. [2] [Total : 7]

4 NJC/H1 Chem Preliminary Examination/02/2024 2 (a) With reference to the Data Booklet, state and explain the trend in the thermal stability of hydrogen halides down the group. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [2] (b) Element A is from Period 4 of the Periodic Table. The first eight ionisation energies of element A, in kJ mol-1, are 947 1798 2735 4837 6043 12310 14300 16800 (i) Identify element A and explain your answer. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [2] (ii) Explain the difference between the first ionisation energy of element A compared to the element to its right on the Periodic Table. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [2]

5 NJC/H1 Chem Preliminary Examination/02/2024 [Turn over (c) A student mixed up the labels of a few bottles in the laboratory. The following are the labels that were mixed up: AlCl3 Al2O3 SiO2 PCl5 The following tests were then conducted to identify the bottles and the observations are recorded: X and Y are insoluble in water while W and Z dissolve readily in water. When tested, the pH of the solution of W is lower than that of Z. Y can react with both HC l (aq) and NaOH (aq), but X can only react with concentrated NaOH. Determine the identities and provide relevant equations to support the answer. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [6] [Total : 12]

6 NJC/H1 Chem Preliminary Examination/02/2024 3 (a) Sulfur dioxide SO2 and sulfites, SO32─, are used as a food preservative to prevent spoilage. (i) Draw the dot and cross diagram of SO2 and SO32─. [2] (ii) Using the Valence Shell Electron Pair Repulsion theory, state and explain the O−S−O bond angle in SO2 and SO32─. ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… [3] (b) The maximum permissible level of sulfite in wine is 250 mg per dm3 of wine. The amount of sulfite can be determined via titration with an oxidising agent. SO32− + H2O → SO42− + 2H+ + 2e− A 25.0 cm3 sample of a wine was acidified, warmed and titrated against KMnO4 to determine its concentration. 19.00 cm 3 of 0.020 mol dm −3 KMnO4 was needed to reach the end point. (i) Write the overall equation for the reaction between SO32− and MnO4−. ……...………………………………………………………………………………… [1]

7 NJC/H1 Chem Preliminary Examination/02/2024 [Turn over (ii) Suggest why the wine sample need to be warmed before the titration? ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… ……...………………………………………………………………………………… [1] (iii) Determine the concentration in mol dm─3, of SO32− in the wine sample. [2] (iv) Hence, determine whether the wine is safe for consumption. [2]

8 NJC/H1 Chem Preliminary Examination/02/2024 (c) Sulfur trioxide is formed from the reaction between SO2 and O2 as shown below: 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) (i) With reference from the Data Booklet, determine the enthalpy change of the reaction. [2] (ii) Write an expression for the equilibrium constant, Kc, for the reaction above, stating its units. [1] (iii) 3 mol dm─3 of SO2 and 2.3 mol dm─3 of O2 were mixed in a closed vessel and allowed to reach equilibrium. The equilibrium concentration of SO2 is found to be 2.4 mol dm−3. Calculate the Kc value. [2]

9 NJC/H1 Chem Preliminary Examination/02/2024 [Turn over The concentrations of the sp