RI Prelim H1 P2

1 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over CANDIDATE NAME CLASS INDEX NUMBER RAFFLES INSTITUTION (JC) PRELIMINARY EXAMINATION 2009 HIGHER 1 CHEMISTRY 8872/02 Paper 2 23 September 2009 2 hours Candidates answer Section A on the Question Paper Additional Materials: Answer Booklet/ Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided on the cover page. 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 paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions on separate answer paper. 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 Section A B6 B7 B8 Total This document consists of 15 printed pages. Raffles Institution Junior College

2 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over Section A (40 marks) This section consists of 5 questions. Answer all questions in the spaces provided. 1. Hydrazine is a hydride of nitrogen with the formula N 2H4. It is a colourless liquid with an ammonia-like odour and is derived from the same ind ustrial chemistry processes that manufacture ammonia. However, hydrazine has physical properties that are more similar to water. It can behave as a weak monoacidic base, forming salts with the more common mineral acids, like sulfuric acids. Hydrazine is a strong reducing agent. Warming hydr azine with nitric acid results in the reduction of nitric acid to nitrogen monoxide, NO w hile hydrazine is oxidised to nitrogen, N 2. A variant of hydrazine, methylhydrazine CH 3NHNH 2, when mixed with dinitrogen tetraoxide, N 2O4, is used as a rocket fuel as this gives a highly exothermic reaction. (a) Draw a dot-and-cross diagram for hydrazine. State t he shape for the hydrazine molecule around the nitrogen atom and the bond angle of H − N− H. [3] (b) Hydrazine can react with sulfuric acid to give a sa lt, hydrazine sulfate, (N 2H5 +)(HSO 4 − ). Explain, with the aid of an equation, if an aque ous solution of hydrazine sulfate is acidic, neutral or basic. [2] For Examiner’s Use

3 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (c) Write a balanced equation for the reaction of nitric acid with hydrazine. [1] (d) The equation between methylhydrazine and dinitrogen tetraoxide may be represented by: 4CH 3NHNH 2(l) + 5N 2O4(l) → 4CO 2(g) + 9N 2(g) + 12H 2O( l) By using the enthalpy changes of formation given be low, calculate the enthalpy change of the reaction. ∆ H f / kJ mol − 1 CH 3NHNH 2(l) +53 N2O4(l) − 20 CO 2(g) − 394 H2O(g) − 242 [2] For Examiner’s Use

4 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (e) Diphosphine, P 2H4, is the phosphorus analogue of hydrazine. Explain why diphosphine is predicted to have a lower boiling point as compared to hydrazine. [2] (f) Hydrazine is used in Wolff-Kishner reduction, a red uction that transforms the carbonyl group of a ketone or aldehyde into a methy lene ( − CH 2) group via a hydrazone intermediate. A reaction scheme is shown below: C O R1 R2 C N R1 R2 NH 2 R1 C R2 H H With reference to the reaction scheme given in the Wolff-Kishner reduction, draw the structure of the carbonyl compound which can gi ve the alkane product as shown: CH 2CH 3 State the type of reaction in Step I. [2] [Total: 12] For Examiner’s Use KOH Step II N2H4 Step I

5 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over 2. The graph shows the logarithm, lg, of the ionizatio n energies for the outermost seventeen electrons in an atom of an element X in Period 4. (a) (i) From the graph above, deduce the group in the Perio dic Table to which X is likely to belong to. Explain your reasoning and sug gest an identity for element X. (ii) Suggest, with the aid of an equation, the pH of the resulting solution of the reaction of the oxide of X with water. [5] For Examiner’s Use 0 5 10 15 Number of electrons removed 0 1 2 3 4 5 lg I.E.

6 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (b) Complete the sketches for elements of the third per iod (sodium to chlorine) to show how each property changes along the period [2] [Total: 7] 3. (a) Define the term ‘ standard enthalpy change of neutralisation ’. [1] (b) When 30.0 cm 3 of 0.40 mol dm − 3 of barium hydroxide were mixed with 40.0 cm 3 of 0.80 mol dm − 3 hydrochloric acid in a polystyrene cup, the temper ature of the solution rose by 4.0 °C. Assume that 4.3 J are required to raise the temp erature of 1 cm 3 of solution by 1.0 °C. (i) Calculate the enthalpy change of neutralisation for the above reaction. Electrical Conductivity Na Mg A l Si P S Cl Ionic radius Na Mg A l Si P S Cl For Examiner’s Use 0

7 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (ii) Suggest why the value in (b)(i) deviates from the theoretical value of − 57.3 kJ mol − 1. [5] (c) The decomposition of hydrogen peroxide is a first order reaction. H2O2 → H 2O + ½O2 ∆Ho = − 98 kJ mol − 1 The uncatalysed reaction has an activation energy of +79 kJ mol − 1. (i) Sketch and label an energy profile diagram for the uncatalysed reaction, showing all relevant energy changes. For Examiner’s Use

8 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (ii) The enzyme, catalase, can be used to speed up the r eaction. Define the term enzyme and explain briefly how it can speed up the reaction. [4] [Total: 10] 4. (a) Phenyl-4-methoxycinnamate, A, is used in various sun-tan creams to absorb excessive ultraviolet radiation. H3CO CH CH C O O CH 2(CH 2)3CH 3 A Explain why A is able to exhibit geometric isomerism. [2] For Examiner’s Use

9 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P02/09 [Turn Over (b) Compound B can be synthesised from the naturally occurring am ino acid phenylalanine by the following route: CH 2CHCO 2H NH 2 CH 2CHCHO NH 2 Compound C CH 2CHCHCO 2H NH 2 OH (i) Suggest the type of reaction in step I. (ii) Draw the structure of the intermediate compound C. (iii) State why a trace amount of base is required to spe ed up the reaction in step II . [3] [Total: 5] Step I Step II HCN Step III Compound B For Examiner’s Use

10 © RAFFLES INSTITUTION (JUNIOR COLLEGE) 2009 8872/P0