2025 SAJC H1 Chem Prelim P2 Questions

1 ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME CLASS 2 4 S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 02 September 2025 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. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. 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. This document consists of 26 printed pages (including this cover page). For Examiner’s Use Section A Q1 25 Q2 12 Q3 12 Q4 11 Section B Q5 20 Q6 20 Total 80

2 1 (a) Aluminium oxide , Al2O3, is a white, crystalline solid with high thermal stability and hardness. (i) Complete the electronic configuration of an aluminium atom. 1s2 …………………………………… [1] (ii) Explain why the first ionisation energy of Al is lower than the first ionisation energy of Mg. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (iii) Draw the ‘dot-and-cross’ diagram of Al2O3. [1] (iv) The ionic radius of Al3+ is 0.050 nm and Ga3+ is 0.062 nm. Explain the difference in ionic radii between Al3+ and Ga3+. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… ……………………………………………………………………………………

3 (a) (v) The melting point of Al2O3 is 2072 °C while the melting point of Ga 2O3 is 1720 °C. Explain the difference in melting points of these two oxides. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (b) (i) Aluminium oxide , Al2O3 and silicon dioxide , SiO2, are both solid ceramic materials with high melting points and are electrical insulators. Explain how differences in their structure and bonding account for their high melting points and poor electrical conductivity. [3] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (ii) Al2O3 and SiO2 have different acid -base behaviour . With the aid of equations, explain the difference in the acid and base behaviour of these two oxides. [4] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [TURN OVER

4 (b) (ii) …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (c) The pH values of two Period 3 chloride solutions are given below. Compound pH of 1.0 mol dm-3 solution AlCl3 3.0 SiCl4 2.0 [4] Suggest explanations for the pH values of the two chloride solutions. Include appropriate equation(s) in your answer. ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. ……………………………………………………………………………………………..… ………………………………………………………………………………………………..

5 (d) Name the shapes and state the bond angles of SiCl4 and PCl3. Explain your answer s using the Valence Shell Electronic Pair Repulsion (VSEPR) Theory. Draw diagrams to illustrate your answers. SiCl4 PCl3 Diagram Shape bond angle [6] ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. ……………………………………………………………………………………………..… ……………………………………………………………………………………………….. [Total: 25] [TURN OVER

6 2 Manganese can form ions that are bonded to oxygen atoms in different oxidation states. Two examples are MnO42– and MnO4–. (a) Both ions of manganese differ in their oxidation number. State the oxidation of each ion. [2] Oxidation state of Mn in MnO42– : ……. Oxidation state of Mn in MnO4– : ……. (b) To standardise Na2S2O3 solution, 25.0 cm3 of 0.025 mol dm–3 KMnO4 was added to an excess of acidified KI solution. The iodine liberated required 22.40 cm3 of Na2S2O3 for reduction. (i) Use the Data Booklet to write an equation for 1. the reaction between and MnO4– ions and I– 2. the reaction between and I– and S2O32– [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (ii) Calculate the concentration of Na2S2O3, in mol dm–3. [2]

7 (c) When K2MnO4 is dissolved in water, the solution appears green. Upon acidification, the green solution , MnO42–, slowly turns into purple MnO4–. This equilibrium is represented by the following equation: 3MnO42– (aq) + 4H+ (aq) 2MnO4– (aq) + MnO2 (s) + 2H2O (l) The equilibrium concentrations are shown in Table 2.1. Table 2.1 Temperature/ °C [MnO42–]/ mol dm–3 [H+]/ mol dm–3 [MnO4–]/ mol dm–3 25 0.010 0.020 0.005 (i) Write the expression for Kc and give its units. [2] (ii) Calculate the value of Kc at 25°C. [1] (iii) Explain the colour change upon acidification of aqueous K2MnO4. [1] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [TURN OVER

8 (c) (iv) When the equilibrium is established at a lower temperature, the value of Kc increases. Deduce whether the reaction is exothermic or endothermic. Explain your answer. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… [Total: 12] 3 Ozone, O3, plays a crucial role in the Earth’s atmosphere by absorbing harmful ultraviolet radiation. It is also widely used for its oxidising and disinfecting properties. For example, ozone can be dissolved in ground water or drinking water for disinfection and water quality enhancement. (a) By considering the number of bonding and non –bonding electron pairs, draw a diagram to show the shape of ozone. In your diagram, clearly state a value of the bond angle. [2]

9 (b) The overall reaction for the decomposition of ozone can be represented as follows: 2O3 → 3O2 The rate of decomposition of ozone in ground water, at pH 8, was investigated and the following results were obtained as shown in Fig. 3.1. The reaction is first order with respect to ozone. Fig. 3.1 Time x 103 / s Concentration of ozone x 10−4 / mol dm−3 0.5 1.0 1.5 2.0 2.5 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 [TURN OVER

10 (b) (i) Define the term order of reaction. [1] …………………………………………………………………………………… …………………………………………………………………………………… (ii) Use the grap