JJC H1 Chemistry 8872 H1 Prelim Paper 2

JURONG JUNIOR COLLEGE PRELIMINARY EXAMINATION 2008 H1 CHEMISTRY PAPER 2 8872 / 2 Monday 18 August 2008 2 hour Name: _______________________ (Index no.:____) Class: 07_____ INSTRUCTIONS TO CANDIDATES Do not open this booklet until you are told to do so. Write your name and index number and class in the spaces at the top of this page. Write in dark blue or black pen in the spaces provided on the Question Paper. You may use a pencil for any diagrams, graphs, or rough working. Do not use highlighters or correction fluid. Answer all questions. FOR EXAMINER’S USE Section A 1 2 3 4 Section B INFORMATION FOR CANDIDATES A Data Booklet is provided. Do not write anything on the Data Booklet. The number of marks is giv en in brackets [ ] at the end of each question or part question. You are advised to sh ow all workings in calculations. You may use a calculator. TOTAL / 80 This question paper consists of 12 printed pages, including this page. [Turn over Page 1 of 12

SECTION A (40 MARKS) Answer all questions in the space provided. 1. World War I is sometimes known as 'the Chemists' War'. Knowledge of chemistry was applied towards developing high expl osives and new methods of warfare such as the large scale use of poison gas. Fritz Haber, a German chemist, worked on t he use of chlorine as a poison gas. The first successful use of chlorine was at Ypres, Belgium, on 22 April 1915. 170 tonnes of chlorine cont ained in 5730 cylinders was released forming a grey- green cloud which drifted across French troops. Chlorine can damage the eyes, nose, throat and lungs and is fatal at concentrations of 1000 ppm and above (1 ppm = 1 mg dm −3). Early counter-measures to chlorine included instructing troops to cover their mouths with gauze pads soaked in sodium hydrogen carbonate solution. Occasionally urine was used instead of the sodium hydrogen carbonate solution. Eventually, more effective counter-measures to chlorine were developed and thus other poison gases were introduced. Victor Grignard, a Nobel Prize-winning chemist, worked on the manufacture of phosgene for France. Phosgene was deadlie r than chlorine but some of the symptoms of exposure only showed up after 24 hours. Thus victims were initially still capable of continuing fighting. The most effective gas used in World War was mustard gas, a blistering agent. Mustard gas did not have to be inhaled but attacked any exposed area of skin. Mustard gas often did not kill outright but it caused horri fic injuries which strained medical resources. (a) (i) Calculate the maximum amount of chlorine gas that could have released from one of the cylinders t hat was used at Ypres on 22 April 1915. (1 tonne = 1000 kg) (ii) Determine the concentration of chlorine gas, in mol dm −3, at 1000 ppm. Page 2 of 12

1. (a) (iii) In an accident, the chlorine gas from one such cylinder was released into a factory room of volume 25.0 m3. Determine if the concentration of ch lorine gas was above the lethal concentration. Assume that the gas was released at room temperature and pressure. [4] (b) (i) The formula of phosgene is COC l 2. Draw the displayed formula for phosgene showing the bond angles clearly. (ii) State the type of hybridisation for carbon in phosgene. ………………………………………………………………………………… (iii) Phosgene contains both σ bonds and π bonds. Explain the terms in italics, drawing diagrams to show these bonds clearly. State the number of σ bonds and π bonds in phosgene. (iv) The boiling point of chlorine is −34.4°C. Predict, with reasons, if phosgene would have a higher or lower boiling than chlorine. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [7] [Total: 11] Page 3 of 12

2. The use of the Data Booklet is relevant to this question. The elements of Period 2 form some of the most common compounds that we come across. (a) Define what is meant by the first ionisation energy of an element E. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [1] (b) Sketch how the first ionisation energies of the elements change from lithium to neon. [1] (c) Explain the difference between the first ionisation energy of (i) carbon and nitrogen ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… (ii) nitrogen and oxygen ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [2] [Total: 4] First ionisation energy (kJ mol −1) proton number 5 0 10 Page 4 of 12

3. (a) The terms strong and weak are used to describe t he strength of an acid. The active ingredient in aspirin is a monobasic acid called acetylsalicylic acid. A 25.0 cm 3 sample of aqueous acetylsalicylic acid was placed in a conical flask. The pH of this solution wa s 2.8. When a titration was performed, 20.00 cm 3 of 0.200 mol dm −3 aqueous sodium hydroxide was required to neutralize the acid. [The formula of acetylsalicylic acid may be simplified as RCOOH for the rest of (a)(i) to (a)(iii).] (i) Calculate the initial concentration of acetylsalicylic acid in the conical flask. (ii) Use your answer in (a)(i) and the above data to show that acetylsalicylic acid is a weak acid. Fully explain your answer. (iii) Write an expression for the acid dissociation constant, K a, for acetylsalicylic acid. Hence determine its Ka value. [5] acetylsalicylic acid : COOH COOCH3 Page 5 of 12

3. (b) The following table shows Ka values for three organic acids. Acid Ka / mol dm−3 CH3COOH 1.75 x 10−5 CH2ClCOOH 1.36 x 10−3 CHCl2COOH 5.53 x 10−2 (i) State and explain the trend in Ka values for the three acids. (ii) How would you expect the acidity of benzoic acid to compare with that of the ethanoic acid? Explain. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [4] [Total: 9] Page 6 of 12

4. A reaction scheme involving cinnamyl chloride is shown below. A B NaOH (aq) heat under reflux CH=CHCH2Cl Stage II Acidified K2Cr2O7 COCH2COOH 2,4-dinitrophenylhydrazine C Stage III CCH2CH2OH CH2NH2 O H Stage IV Cinnamyl chloride Stage I CCH2COOH CN O H heat under reflux Page 7 of 12

4. (a) (i) Draw the structures of compounds A to C in the boxes provided. (ii) State the type of reaction and r eagents and conditions required for Stages II to IV. Stage Reagents and conditions Type of Reaction II III IV (iii) Write a balanced equation for the reaction in Stage IV. ………………………………………………………………………………… [10] Page 8 of 12

4. (b) Describe a laboratory test which will distinguish the following pairs of compounds from each other. You should include the reagents and conditions needed and the expected observations for each compound in your answer. (i) and W X (ii) and Y Z [6] [Total : 16] COOCH2CH3 COOC(CH3)3 CH3 CH3 Page 9 of 12

SECTION B (40 MARKS) Answer two of the three questions in this section on separate paper. 5. (a) Ethane is a major component in nat ural gas which an important petrochemical feedstock. An experiment was carried out as follows to determine the enthalpy change of combus tion of ethane, contained in the gas cylinder of a gas stove. A large beaker of wate r was placed on the gas stove and heated. The temperature rise of the water was recorded. The gas cylinder was also weighed before and after heating to det ermine the