2023 NJC H2 Chemistry Prelim Paper 3 QP

1 NJC SH2 Preliminary Examination 9729/03/23 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/03 14 September 2023 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 /20 2 /16 3 /24 Section B 4 /20 5 /20 Paper 3 Total /80 This document consists of 32 printed pages.

2 NJC SH2 Preliminary Examination 9729/03/23 Section A Answer all the questions in this section. 1 (a) Table 1.1 list physical properties of some Period 4 elements. Table 1.1 property K Ca Fe As Se relative atomic mass 39.1 40.1 55.8 74.9 79.0 atomic radius (metallic) / nm 0.197 0.126 melting point / K 1112 1808 density / g cm−3 1.54 7.86 1st I.E. / kJ mol−1 944 941 2nd I.E. / kJ mol−1 3070 1150 (i) Explain why the atomic radius of Fe is less than that of Ca. [2] (ii) Use relevant data from Table 1.1 to explain why the density of Fe is significantly greater than that of Ca. (no calculations are required) [2] (iii) Suggest why the melting point of Fe is significantly higher than the melting point of Ca. [2] (iv) With reference to the electronic configuration of K and Ca, explain why the 2nd I.E. of Ca is lower than that of K. [2] (v) With reference to the electronic configurations of As and Se, explain why the 1st I.E. of Se is lower than that of As. [2] …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ……………………………………………………………………………………………..

3 NJC SH2 Preliminary Examination 9729/03/23 [Turn over …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ……………………………………………………………………………………………..

4 NJC SH2 Preliminary Examination 9729/03/23 (b) The Fischer-Tropsch process involves converting a mixture of carbon monoxide and hydrogen, known as syngas, into hydrocarbons, in the presence of catalysts. One such reaction is shown below: CO(g) + 3H2(g) CH4(g) + H2O(g) ∆H < 0 (i) Write an expression for the equilibrium constant, Kp, for this reaction, and state its units. [2] (ii) A mixture of CO and H 2 was introduced into a sealed vessel and heated to 1200 K. At equilibrium, it was found that the total pressure was 32 atm, and the mole fractions of CO and CH4 were 0.5 and 0.12 respectively. Calculate the equilibrium partial pressures of all gases, and hence calculate the value of Kp. [3] (iii) Higher temperatures and higher pressures can lead to faster reactions. However, in commercial facilities that use the Fischer-Tropsch process, this was avoided. Explain why. [2] Transition m etals such as iron or cobalt, are commonly used as catalysts in the Fischer-Tropsch process. (iv) State the type of catalysis in the Fischer-Tropsch process. [1] (v) Outline the mode of action of the catalyst in the Fischer-Tropsch process. [2] …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. ……………………………………………………………………………………………. …………………………………………………………………………………………….

5 NJC SH2 Preliminary Examination 9729/03/23 [Turn over …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. …………………………………………………………………………………………….. [Total: 20]

6 NJC SH2 Preliminary Examination 9729/03/23 2 Iodine is found naturally in compounds in many different oxidation states. (a) Iodide ions, I−, react with acidified H2O2(aq) to form iodine, I2, and water. The resultant mixture is then shaken with cyclohexane, C6H12, to extract the I2. Cyclohexane is immiscible with water. (i) Identify the role of H2O2(aq) in its reaction with I− ions in acidic conditions. Write an ionic equation for the reaction.