IJC 2008 H2 Chemistry Prelim II Paper2

INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS 2 in preparation for General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured Candidates answer on the Question Paper Additional Materials: Data Booklet 9746/02 15 September 2008 1 hour 30 min READ THESE INSTRUCTIONS FIRST Write your index number, name and civics group on all the work you hand in. Write in dark blue or black pen. You may use pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. For Examiner’s Use Section A 1 13 2 11 3 8 4 12 5 16 Significant Figures Handwriting Total 60 Answer all questions in the space provided. A Data Booklet is provided. You are advised to show all working in calculations. You are reminded of the need for good English and clear presentation in your answers. You are reminded of the need for good handwriting. Your final answers should be in 3 significant figures. You may use a calculator. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This document consists of 15 printed pages and 1 blank page. [Turn overInnova Junior College

2 © INNOVA 2008 9746/02 [Turn over For Examiner’s Use Answer ALL questions on the space provided 1 Aspirin, or acetylsalicylic acid is used as an anti-inflammatory medication. It has been established that low doses of aspirin may be given immediately after a heart attack to reduce the risk of another heart attack or of the death of cardiac tissue. Aspirin has the structural formula: (a) Paracetamol and aspirin are commonly used for the relief of fever, headaches, and other minor aches and pains. Median lethal dose, LD50 of a toxic substance or radiation is the dose required to kill half the members of a tested population. LD 50 figures are frequently used as a general indicator of a substance's acute toxicity. The LD 50 of Aspirin is 1100 mg kg –1 of body mass and of paracetamol is 338 mg kg–1of body mass. (i) Suggest and explain whether aspirin or paracetamol is more toxic. ……………………………………………………………………………....……….... ……………………………………………………………………………....……….... (ii) Calculate the minimum number of 325 mg aspirin tablets that will be toxic to a 50 kg person. [2]

3 © INNOVA 2008 9746/02 [Turn over For Examiner’s Use (b) The synthesis of aspirin is classified as an esterification reaction, where the alcohol group from the salicylic acid reacts with an acid derivative (acetic anhydride), yielding aspirin and acetic acid as a by-product. Small amounts of sulphuric acid are often used as a catalyst. (i) Why is aspirin kept in dry conditions? …………………………………………………………………………….………….... ………………………………………………………………………………………..... [1] (ii) Suggest a method (include all reagents and conditions) to re-form salicylic acid from aspirin. Write an equation for this conversion. Method: …………………………………………………………………… Reagent(s) and condition(s): …………………………………………… Equation: [2] (iii) Suggest a simple chemical test to differentiate salicylic acid from aspirin. Reagent(s) and condition(s): ………………………………………………………… Observations for salicylic acid: …………………………………………………………………….….... aspirin:……………………… …………………………………………………….….... [2]

4 © INNOVA 2008 9746/02 [Turn over For Examiner’s Use (iv) Predict, with reasons, whether aspirin is a stronger or weaker acid than acetic acid. …………………………………………………………………………………….….... …………………………………………………………………………………….….... …………………………………………………………………………………….….... …………………………………………………………………………………….….... …………………………………………………………………………………….….... [2] (c) A large shipment of salicylic acid is contaminated with boric oxide, B(OH) 3. It looks like salicylic acid which is a white powder. The heat of combustion of salicylic acid at constant volume is known to be –3.00 x 103 kJ mol–1. Boric oxide does not burn because it is fully oxidized. When a 3.56 g sample of contaminated salicylic acid is burned in a bomb calorimeter, the temperature increases by 2.5 oC. From previous measurements, the heat capacity of the calorimeter is known to be 13.62 kJ K–1. (i) Define standard enthalpy change of combustion of salicylic acid. …………………………………………………………………………………….….... ………………………………………………………………………………….…….... ……………………………………………………………………………….………….. [1] (ii) Calculate the percentage by mass of boric oxide in the sample of contaminated salicylic acid. [3] [Total: 13]

5 © INNOVA 2008 9746/02 [Turn over For Examiner’s Use 2 Hydrazine is a chemical compound with the formula N 2H4. It has an ammonia-like odour, and is derived from the same industrial chemistry processes that manufacture ammonia. However, hydrazine has physical properties that are more similar to those of water. Hydrazine is used as rocket fuel and to prepare the gas precursors used in air bags. (a) Draw the Lewis structure for the hydrazine molecule. State its shape and indicate the H–N–H bond angle. Shape: ………………………. [2] (b) (i) Calculate the volume occupied by 1 mole of ideal gas at a pressure of 1.5 atm and 300 K. [1] (ii) At a pressure of 1.5 atm and 300K, 1 mole of gaseous hydrazine occupies a volume 20.0 dm 3. Explain the difference in the volume occupied by hydrazine and the volume calculated in (i). ……………………………………………………………………………………….... ……………………………………………………………………………………….... ……………………………………………………………………………………….... [1] (iii) Under what conditions of temperature and pressure would you expect gaseous hydrazine to occupy the same volume as that calculated in (i)? ……………………………………………………………………………………….... [1]

6 © INNOVA 2008 9746/02 [Turn over For Examiner’s Use (iv) Assuming that gaseous hydrazine is placed under the conditions specified in (iii), sketch the graph of pressure against the reciprocal of volume for a given amount of hydrazine at constant temperature. Pressure 1 Volume 1 Volume [1] (c) Liquid hydrazine has alkaline properties comparable to those of ammonia but ammonia is fifteen times stronger. N2H4 + H2O N2H5 + + OH– (i) What feature of the hydrazine molecule enables it to act as a base? ……………………………………………………………………………………….... ……………………………………………………………………………………….... [1] (ii) Write an expression for the base dissoci