AJC_Prelims H2 Chem Paper 2_Question paper

NAME:______________________________ PDG:__________ Register No: _____ ANDERSON JUNIOR COLLEGE Preliminary Examination 2008 CHEMISTRY 9746/02 Higher 2 15 September 2008 Paper 2 Structured 1 hour 30 minutes Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, PDG and register number on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer ALL the questions. 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. For Examiner’s Use Q1 Q2 Q3 Q4 Q5 Total This document consists of 12 printed pages. AJC/H2 Chemistry/Prelims2008 [Turn over

2 AJC/H2 Chemistry/Prelims2008 [Turn over 1 (a) (i) Define, by means of an equation, what is meant by the first ionisation energy of an element, M. (ii) Phosphorus and iodine are two elements found in Period 3 and Period 5 of the Periodic Table respectively. Suggest a reason why they have similar first ionisation energies. [3] (b) When iodine is added to a solution of white phosphorus, P 4, in carbon disulphide at room temperature, phosphorus triiodide is formed. (i) Write an equation for the formation of phosphorus triiodide from white phosphorus. (ii) Draw a ‘dot-and-cross’ diagram of the phosphorus triiodide molecule and name its shape. Shape of molecule (iii) Unlike phosphorus triiodide, phosphorus pentaiodide, PI5, is highly unstable and cannot be prepared under room temperature. Suggest a reason for this. [4]

3 (c) Phosphorus triiodide is widely used in organic chemistry for converting alcohols to alkyl iodides. Phosphorus acid, H3PO3, is formed as a by-product. PI3 + 3ROH → 3RI + H3PO3 Phosphorus acid has the following structure. P O H O O H H It is a dibasic acid and the two corresponding acid dissociation values are: Ka (1) = 1.0 × 10−2 mol dm−3 Ka (2) = 2.5 × 10−7 mol dm−3 (i) Circle the acidic proton(s) present in the structure of phosphorus acid shown above. (ii) Write equations to illustrate the dissociation corresponding to each of the Ka values. Ka (1) Ka (2) (iii) Why is the second acid dissociation value smaller than the first? (iv) Briefly explain why H3PO3 is not tribasic. [4] [Total: 11] AJC/H2 Chemistry/Prelims2008 [Turn over

4 2 (a) (i) Hydrogen chloride can be prepared by heating sodium chloride with concentrated sulphuric acid. Write an equation for the formation