MSHS Chem Prelim P2

Class/ Index Number / Centre Number/ ‘O’ Level Index Number / Name MARIS STELLA HIGH SCHOOL PRELIMINARY EXAMINATION SECONDARY FOUR CHEMISTRY 6092/02 Paper 2 22 August 2025 1 hour 45 minutes Candidates answer on the Question Paper. No additional materials are required. READ THESE INSTRUCTIONS FIRST Write your class, index number, Centre number, O level index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer one question. Write your answers in the spaces provided. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 22. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A Section B Total This document consists of 22 printed pages. 70 10 80

2 Section A Answer all questions in this section in the spaces provided. 1 The structures of some carbon-containing substances, A, B, C, D, E and F are shown in Fig 1.1. Fig. 1.1 (a) Use the letters A, B, C, D, E and F to answer the following questions. Each letter may be used once, more than once or not at all. (i) Which substance is a saturated hydrocarbon? ……………………………………………………………………………………………...[1] (ii) Which substance has a giant molecular structure? ……………………………………………………………………………………………...[1] (iii) Which substance is a product of respiration? ……………………………………………………………………………………………...[1] (iv) Which substance is in the same homologous series as ethene? ……………………………………………………………………………………………...[1] (v) Which substance is found in limestone? ……………………………………………………………………………………………...[1] A B C D E F

3 (b) Explain why substance B in the atmosphere is increasing and why planting more trees is not a long-term solution to the increase in the amount of B. ……………………………………………………………………………………………................ ……………………………………………………………………………………………................. …………………………………………………………………………………………….............[2] [Total: 7]

4 2 Lithium is a metal and lithium chloride is a compound. The structure and properties of these substances are very different. (a) Explain using ideas about bonding and structure , how the particles in lithium and lithium chloride are held together. ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………....[2] (b) Table 2.1 below shows the melting and boiling points of lithium and lithium chloride. Table 2.1 melting point / oC boiling point / oC lithium 180.5 1342 lithium chloride 605.0 1382 Using the information from Table 2.1, explain what can be deduced about the forces of attraction holding the particles together in lithium and lithium chloride. ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………....[2] (c) Two students, A and B, are comparing the properties of lithium and lithium chloride at room temperature . Student A states that both lithium and lithium chloride can conduct electricity, but Student B states that only lithium can conduct electricity. State whether Student A, Student B, or neither student is correct. Explain your answer. ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………....[3]

5 (d) Students A and B then went on to discuss the bonding in another substance, calcium fluoride. Explain, in terms of electrons, how the bonds in calcium fluoride are formed. ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ……………………………………………………………………………………………........ ………………………………………………………………………………………………[2] [Total: 9]

6 3 Chlorine dioxide, ClO2, was the first oxide of chlorine to be discovered. Although unstable as a liquid or gas, it is now produced on a very large scale for the bleaching of wood pulp and water treatment. Chlorine dioxide has a complex bonding structure. The chlorine atom in the molecule has an unpaired electron, which is not involved in bonding, contributing to its reactivity. The structure of a chlorine dioxide molecule can be represented as shown. O = Cl = O (a) Draw a ‘dot & cross’ diagram to show the bonding in a chlorine dioxide molecule . Show outer shell electrons only. [2] (b) Chlorine dioxide was first obtained by scientist and inventor, Humphry Davy. It was formed by the hazardous disproportionation reaction of chloric acid, HClO3. 3HClO3 → 2ClO2 + HClO4 + H2O Disproportionation is a type of redox reaction in which the same element is both oxidised and reduced. Which element in the reaction has undergone disproportionation? Explain your answer using oxidation states. ……………………………………………………………………………………………………….. ……………………………………………………………………………………………………….. ……………………………………………………………………………………………………..[2] (c) Chlorine dioxide can also be produced by reacting sodium chlorate( III), NaC lO2 with chlorine. The other product is sodium chloride. (i) Write an equation for the reaction. ………………………………………………………………………………………………[1] (ii) Which is the oxidising agent? Explain your answer. ………………………………………………………………………………………………… ………………………………………………………………………………………………[2] [Total: 7]

7 4 Sulfuric acid and malonic acid are both dibasic acids. Malonic acid is a white crystalline solid which is soluble in water. It melts at 135 °C. The structural formula of malonic acid is given below. HOOC–CH2–COOH (a) (i) Write the molecular formula of malonic acid. ………………………………………………………………………………………..[1] (ii) When malonic acid is thermally decomposed, carbon dioxide and a simpler carboxylic acid are formed. Deduce the name and formula of this acid. ………………………………………………………………………………………..[2] (iii) (iv) Name the product when the carboxylic acid in (a)(ii) is mixed with ethanol and heated in the presence of concentrated sulfuric acid. ………………………………………………………………………………………..[1] Draw the structural formula of the product formed in (a)(iii). [1] (b) Suggest why a solution of malonic acid, of concentration 0.2 mol/dm3, has a higher pH than sulfuric acid of the same concentration. ……………………………………………………………………………………………….[1] [Total: 6]

8 5 Aqueous hydrogen peroxide is often used in households as a bleaching agent as well as a disinfectant among other uses. At room temperature, aqueous hydrogen peroxide decomposes very slowly to form water and oxygen. The decomposition of hydrogen peroxide can be represented by the equation below. (a) Explain in terms of bond making and bond breaking why this reaction is exothermic. ………………………………………………………………………………………………… ………………………………………………………………………………………………[2] (b) The decomposition of hydrogen peroxide is speeded up by adding powdered manganese(IV) oxide. An experiment was carried out with three samples of hydrogen peroxide placed in conical flasks labelled P, Q and R. An equal mass of powdered manganese(IV) oxide was added to each conical flask. The mass of the conical flasks and their contents were measured at regular time intervals, and a graph of mass was plotted aga inst time. The results are shown in Fig. 5.1. Fig. 5.1