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° ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [4] [Total: 8] 3 (a) Cracking is a chemical process carried out to break down longer chain alkanes that predominate in crude oil into shorter chain alkanes and alkenes. (i) Give a reason on why cracking is important in the petroleum industry? ……………………………………………………………………………………………… [Turn Over

7 3 (a) (ii) Oil refineries carry out cataly tic reforming to convert straight chain hydrocarbon, in the presence of a catalyst, to an aromatic molecule such as benzene. Describe a laboratory test which will distinguish benzene from benzaldehyde. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [3] (b) In a motor car engine, petrol vapour and air are ignited by an electric spark, producing an explosive reaction which drives the pistons of the engine. Why are products of incomplete combustion formed in the car engine from the combustion of the petrol vapour? ……………………………………………………………………………………………… [1] (c) Cracking produces pentene with production exceeding one million tonnes annually in the United States. Pentene is able to display structural isomerism. Draw all possible isomers of pentene. [4] [Total: 8] [Turn Over

4 In an analytical chemistry laboratory, samples of unknown elements Q to Z were passed through a plasma torch. Their first ionisation energies were recorded and plotted as shown below. Elements Q to Z are consecutive elements in the Periodic Table and have atomic numbers below 20. 0 2000 4000 6000 8000 QRSTUVW XYZ Elements 1st IE / kJ mol -1 (a) Identify the Group to which element W belong to in the Periodic Table and hence state the identity of element W. Element W belongs to Group …………….. Identity of element W: ………………………… [2] (b) (i) State the electronic configurations of the ions, W+ and X+. W+ : ………………………………………………………………………………… X+ : …………………………………………………………………………………. [Turn Over 8

4 (b) (ii) Predict, with reasons, how the second ionisation energy of X differ from that of W. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [4] (c) Explain the decrease in first ionisation energy between elements Y and Z. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [2] [Total: 8] 5 (a) The following diagram shows a reaction scheme of sodium. Sodium excess O 2 E H2O F NaCl Reagent X Reagent Y (i) Identify the molecular formulae for the following compounds: E: …………………………………………. F: …………………………………………. Reagent X: ………………………………. Reagent Y: ………………………………. [Turn Over 9

10 5 (a) (ii) Write an equation for the reaction between F and aluminium oxide. State the type of reaction. Equation: ……………………………………………………………………………………… Type of reaction: ………………………………………………….. [4] (b) The melting points of three chlorides are given below. Compound Formula Melting Point /°C Sodium chloride NaCl 801 Potassium chloride KCl 772 Aluminium chloride AlCl3 180 Explain the difference in the melting points between: (i) NaCl and KCl ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (ii) NaCl and AlCl3 ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [4] [Total: 8] [Turn Over