2023 SAJC H2 Chem Prelim P2 (QP)

ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 2 S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 30 August 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work that you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. This document consists of 28 printed pages (including this cover page). For Examiner’s Use Q1 9 Q2 21 Q3 17 Q4 9 Q5 19 Total 75

2 1 (a) Table 1.1 lists the number of protons, neutrons and electrons in five different particles. Each particle may be an atom, an anion or a cation. Table 1.1 particle number of protons number of neutrons number of electrons A 17 18 17 B 17 20 17 C 17 20 18 D 18 22 18 E 18 22 17 F 19 20 19 G 19 20 18 (i) Use the information in Table 1.1 to identify • the two particles which are a pair of isotopes of the same element __________________________________________________________ • the uncharged particle with no unpaired electrons __________________________________________________________ [2] (ii) Deduce which particle, F or G is smaller. Explain your answer. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………………

3 (b) Phosphorus pentachloride, PC l5, is a useful reagent in organic synthesis. It exists in equilibrium with PCl3 and chlorine gas as shown below: PCl5 (g) PCl3 (g) + Cl2 (g) ΔH = +124 kJ mol‒1 At equilibrium, at 200 °C and a total pressure of 5 atm, 40% of PC l5 is dissociated. (i) Write an expression for Kp for the above equilibrium. [1] ………………………………………………………………………………………… …. (ii) Calculate a value for Kp at 200 °C and state its units. [2] (iii) Predict and explain the effect of increasing the temperature on the value of Kp. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [Total: 9]

4 2 (a) Table 2.1 gives data about some physical properties of the elements potassium, calcium and iron. Table 2.1 Property potassium calcium iron relative atomic mass 39.1 40.1 55.8 atomic radius (metallic) / nm 0.243 0.197 0.126 ionic radius (charge) / nm 0.138 (1+) 0.099 (2+) 0.061 (2+) melting point / K 337 1112 1811 density / g cm−3 0.89 1.54 7.87 electrical conductivity / 106 S m−1 0.14 0.298 1.00 (i) Explain why the atomic radius of calcium is less than that of potassium. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… (ii) Use relevant data from Table 2.1 to suggest why the density of calcium is greater than that of potassium. You may assume that both elements have the same packing arrangement of atoms. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………………

5 (iii) Describe the structure and bonding in calcium with the aid of a labelled diagram. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… (b) The high conductivity of iron is a consequence of its electronic configuration. (i) Complete the electronic configuration of an iron atom and Fe2+ ion. [1] Fe 1s2 2s22p6 ________________ Fe 2+ 1s2 2s22p6 ________________ (ii) Despite its high electrical conductivity, iron is rarely used in electrical wires, unlike copper. Apart from its physical properties, suggest a reason why iron is less preferred than copper in electrical wiring. [1] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………………

6 (iii) Iron can form octahedral complexes. In an octahedral complex, the d subshell of a transtion metal ion is split into two energy levels. On the Cartesian axes in Fig. 2.1, draw a fully-labelled diagram of one d orbital at the lower energy level in an octahedral complex. [1] Fig. 2.1 (iv) Describe two ways in which compounds containing Fe2+ ions are different from those containing Ca2+ ions in terms of their chemical behaviour. [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………………

7 (c) Iron(II) compounds are generally only stable in neutral, non -oxidising conditions. It is difficult to determine the lattice energy of FeO experimentally. (i) Use data from the Data Booklet and relevant data in Table 2.2 to construct a labelled Born-Haber cycle to determine the enthalpy change of lattice energy of FeO(s). Table 2.2 ΔH/kJ mol−1 Enthalpy change of atomisation of Fe(s) +416 Sum of first and second electron affinity of O(g) +657 Enthalpy change of formation of FeO(s) -272 [3] 0 energy

8 (ii) State and explain how the lattice energy of FeO(s) compares to the lattice energy of CaO(s). [2] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… (iii) Most naturally occurring samples of iron( II) oxide are found as the mineral wüstite. Wüstite has formula Fe20Ox. It contains both Fe2+ and Fe3+ ions. 90% of the iron is present as Fe2+ and 10% is present as Fe3+. Deduce the value of x. [1]

9 (d) Heating of FeO results in the formation of Fe3O4, as shown. 4FeO → Fe + Fe3O4 ------------------------reaction 1 Each formula unit of Fe3O4 contains one Fe2+ and two Fe3+ ions. (i) Deduce the type of reaction in reaction 1. Explain your answer. [1] ………………………………………………………………………………………… ………………………………………………………………………………………… (ii) Molten Fe3O4 can be electrolysed using inert electrodes to form Fe. Calculate the maximum mass of iron metal formed when molten Fe 3O4 is electrolysed for six hours using a current of 50 A. Assume the one Fe2+ and two Fe3+ ions are discharged at the same rate. [3] [Total: 21]

10 3 (a) Sucrose can be hydrolysed in the presence of dilute acids. This reaction can be represented by: sucrose + water → glucose + fructose In an investigation of the kinetics of this reaction, sucrose was reacted in two separate experiments with different concentrations of HCl. The following graph was obtained with the initial concentration of sucrose in the reaction mixture = 0.05 mol dm –3. The concentrations cited in the graph indicate the initial concentrations of each reagent in the reaction mixture. 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 [HCl]= 0.5 mol dm–3 [HCl]= 1.0 mol dm–3 time / s [sucrose] / mol dm–3