P.M. MONDAY, 11 May minutes

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1 Candidate Name Centre Number 2 Candidate Number GCE AS/A level 333/01 CHEMISTRY CH3a P.M. MONDAY, 11 May minutes FOR EXAMINER S USE ONLY Question Mark ADDITIONAL MATERIALS In addition to this examination paper, you will need a: calculator; copy of the Periodic Table supplied by WJEC. Refer to it for any relative atomic masses you require. INSTRUCTIONS TO CANDIDATES Write your name, centre number and candidate number in the spaces at the top of this page. Answer all questions in the spaces provided. INFORMATION FOR CANDIDATES The number of marks is given in brackets at the end of each question or part-question. The maximum mark for this paper is 30. Your answers must be relevant and must make full use of the information given to be awarded full marks for a question. You are reminded that marking will take into account the Quality of Written Communication used in all written answers. Page 9 may be used for rough work TOTAL MARK JD*(S )

2 2 Examiner Candidates are advised that answers to all questions should be brief and concise; lengthy extended responses are not required. 1. A student measured the rate of the reaction of 1-bromobutane with sodium hydroxide. The equation for the reaction is C 4 H 9 Br + NaOH C 4 H 9 OH + NaBr The experiment was carried out by measuring the decrease in concentration of the NaOH as outlined below. 1. Equal volumes of 1-bromobutane and sodium hydroxide of the same concentration were placed in separate flasks in a water bath at 25 C and allowed to reach the bath temperature. 2. The two solutions were rapidly mixed as a stopwatch was started. 3. After exactly five minutes, a 10 cm 3 sample of the mixture was removed by pipette, rapidly transferred to a flask containing 50 cm 3 of iced water and the remaining unreacted NaOH titrated with standard HCl from a burette to an endpoint using phenolphthalein indicator. 4. Step 3 was repeated at several further five minute intervals and the results obtained are tabulated below. Time / minutes Volume HCl / cm (a) (i) Plot the results above on the graph grid provided opposite and draw the curve. (The first point is already plotted.) [3] (ii) Use your plot to calculate the initial rate of reaction. [2]

3 3 Examiner volume HCl / cm time / minutes 30 (b) Answer the following questions about the procedure used in the experiment. (i) Suggest why the pipetted samples were added rapidly to excess iced water. [1] (ii) Explain why the rate decreases as the reaction proceeds. [1] (iii) Suggest one method of measuring the rate of a reaction which does not require samples to be taken at timed intervals. [1] Turn over.

4 4 Examiner 2. The graph below was obtained from a student experiment to determine the enthalpy change (ΔH) of solution of solid ammonium nitrate in water which used 50 0 g of water and mol of ammonium nitrate temperature / C time / minutes 12 time of mixing

5 5 Examiner (a) (i) Use the graph to estimate the maximum temperature change (ΔT). [2] (ii) Then calculate ΔH, using the equation ΔH = 4 18mΔT n Jmol 1, where m is the mass of water in grams and n is the number of moles of ammonium nitrate. [2] (b) State two common sources of error in this experimental procedure to determine enthalpy changes (ΔH) in solution. [2] Total [6] Turn over.

6 6 Examiner 3. A student determined the concentration of a solution of sulphuric acid by titrating it against a standard solution made by dissolving 10 6 g of sodium carbonate (M r = 106) in distilled water to give 1 dm 3 of solution. A burette was rinsed twice with small volumes of acid and filled to above the zero mark using a small funnel. The funnel was removed and the acid level brought exactly to the 0 00 cm 3 mark cm 3 of the sodium carbonate solution was placed in a conical flask with a suitable indicator and the acid added while swirling the flask contents. When the indicator gave signs of change, the titration was halted, the flask walls washed with water and the titration continued, drop by drop, to the end-point. Three titrations gave readings of 20 75, and cm 3, respectively. (a) Answer the following questions on the procedure used. (i) State why the burette was rinsed with the acid before filling. [1] (ii) State why the funnel was removed. [1] (iii) State and explain whether there was any need for the acid level to be set exactly on zero. [1] (iv) State why the flask contents were swirled during the titration. [1]

7 7 Examiner (b) (i) State, giving a reason, whether you would include the reading of cm 3 in calculating the mean titration. [1] (ii) The equation for the acid/carbonate reaction is given below. H 2 SO 4 + Na 2 CO 3 Na 2 SO 4 + CO 2 + H 2 O Use the data and results above to calculate the concentration of the acid solution. [3] Turn over for question 4 Turn over.

8 8 Examiner 4. A sequence of organic reactions is shown below. elimination hydrolysis CH 3 CH 2 Cl CH 2 = CH 2 CH 3 CH 2 OH A B C oxidation CH 3 COOH D Each of these organic compounds may be identified by one of the tests in the table below. Complete the table by inserting the letter for the correct compound and stating what is observed. [8] Test Heat with NaOH(aq), acidify with HNO 3 and then add AgNO 3 (aq) Add NaHCO 3 (aq) and test the product Compound Observation Add bromine water Warm with acidified dichromate(vi) solution [30]

9 9 Examiner Rough Work

10 CH3a 1. (a) (i) Points correctly plotted (2) lose ½ for each error Curve quality (1) [3] (ii) 0.60 ± 0.06 (2); ± 0.10 (1) [2] (b) (i) To stop or freeze the reaction at the time of sampling [1] (ii) Concentration of reactants is decreasing / there are fewer collisions between reactants [1] (iii) Measure ph of solution over time, will decrease as NaOH used up [1] 2. (a) (i) minus 10 C ± 0.5 C (2); ±1.0 C (1) [2] (ii) lose ½ for incorrect sign, consequential on value in (i) [2] (b) Any two from: heat loss to / gain from surroundings poor mixing / temperature not steady before start of reaction extrapolation errors etc. [2] 12 Total [6] 3. (a) (i) To remove water or impurities / to ensure that acid at the correct concentration was present [1] (ii) To avoid error in burette reading / drips from funnel etc. [1] (iii) No, since a difference is being measured [1] (iv) To ensure rapid and complete mixing of reactants [1] (b) (i) Would not, too far out from other readings [1] (ii) Concentration of carbonate = 10.6 = (1) Stoichiometry of reaction is 1:1 (1) cm 3 of acid is equivalent to cm 3 of carbonate therefore concentration acid = = mol dm (1) [3]

11 4. Letter or formula 1 mark each for A-D A (1) white precipitate (1) D (1) gas evolved (½) turns limewater milky (½) - no credit for CO 2 evolved B (1) bromine water decolorised (1) C (1) colour change from orange to green (1) goes green (½) Paper Total [30] 13

Advanced Subsidiary Unit 3: Chemistry Laboratory Skills I. Wednesday 14 January 2015 Morning Time: 1 hour 15 minutes

Write your name here Surname Other names Pearson Edexcel International Advanced Level Centre Number Chemistry Advanced Subsidiary Unit 3: Chemistry Laboratory Skills I Candidate Number Wednesday 14 January