SAJC_H1 Prelims Paper 2 Questions

Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Chemistry Higher 1 8872/02 Paper 2 9th September 2008 2 hours Candidates answer Section A on the question Paper Additional Materials: Answer Paper, Data Booklet READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen on both sides of the paper You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions Section B Answer two questions on separate answer paper At the end of the examination, fasten all your work securely. The number of marks is given in brackets [ ] at the end of each question or part question. For examiner’s use Section A Section B Total This document consists of 16 printed pages including this page.

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3 Section A Answer all questions in this section in the spaces provided. 1 (a) An organic acid has the following composition by mass: C, 26.64%; H, 2.22%; O, 71.14%. Analysis shows that it is a dibasic acid. 4.5 g of the acid requires 50.00 cm3 of 2.00 mol dm-3 sodium hydroxide for complete neutralisation. (i) Calculate the empirical formula of the acid. (ii) Calculate the relative molecular mass of the acid. (iii) Determine the molecular formula of the acid. [4] [Turn Over

4 1 (b) Ethanedioic acid is able to act as a reducing agent. In a reaction, 25.0 cm3 of potassium manganate(VII) solution is required to react completely with a 6.75 g sample of the acid. The acid is oxidised to carbon dioxide, and manganate(VII) ions is reduced to manganese(II) ions. (i) Write a balanced half equation for the oxidation of the acid. ……………………………………………………………………………………………… (ii) Calculate the number of moles of acid used in the reaction. (iii) Calculate the concentration of the manganate(VII) solution used. [4] [Total: 8] [Turn Over

5 2 (a) Draw dot-cross diagrams of the following molecules in the spaces provided. Hence, predict shapes and the bond angles in these molecules. (i) Cl2O Shape of molecule: …………………….. Bond angle: …………… (ii) SO 3 Shape of molecule: …………………….. Bond angle: …………… [4] [Turn Over

6 2 (b) Explain each of the following observations as fully as you can: (i) Silicon oxide melts at 1830°C but silicon chloride melts at 58°C. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… (ii) The bond angles in the H2O, H2S and H2Se decreases as shown: Molecule H 2O H 2S H 2Se Bond angle 109° 92° 83° ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………