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GCE MAY 2007 : (AS 3) Practical Examination 2

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Centre Number 71 Candidate Number ADVANCED SUBSIDIARY (AS) General Certificate of Education 2007 Chemistry assessing Module 3: Practical Examination 2 ASC32 Assessment Unit AS 3 [ASC32] FRIDAY 18 MAY, MORNING TIME 2 hours 30 minutes. INSTRUCTIONS TO CANDIDATES Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all four questions. Write your answers in the spaces provided. INFORMATION FOR CANDIDATES The total mark for this paper is 90. Questions 1 and 2 are practical exercises each worth 25 marks. Question 3 is a planning exercise worth 20 marks. Question 4 is a written question testing aspects of experimental chemistry worth 20 marks. You may have access to notes, textbooks and other material to assist you. A Periodic Table of Elements (including some data) is provided. For Examiner s use only Question Number 1 2 3 4 Total Marks ASC3aS7 2927 Marks 1 Observation/deduction Safety goggles must be worn at all times and care should be exercised during this practical examination. (a) You are provided with a mixture of two salts, labelled A, which have a common cation. Carry out the following experiments on the mixture. Record your observations and deductions in the spaces below and identify the two salts. Experiment Observations Deductions 1 (a) Make a solution of A by dissolving a half-spatula measure of A in a test tube half-full of dilute nitric acid. (b) Place one cm3 of the solution of A in a test tube with one cm3 of silver nitrate solution. (c) Place one cm3 of the solution of A in a test tube and add one cm3 of barium chloride solution. 2 (a) Using a fume cupboard, place a spatula measure of A in a test tube and add ten drops of concentrated sulphuric acid. (b) Test the gas given off with damp Universal Indicator paper. (c) Repeat part (a) in the fume cupboard, and test the gas given off using the stopper from a bottle of concentrated ammonia solution. 3 Place a half-spatula measure of A on a watch-glass and add three drops of concentrated hydrochloric acid. Use a clean loop of nichrome wire to place this acidified sample of A in a blue Bunsen flame. Name the two salts in A ____________________________________________ ASC3aS7 ASC3aS7 2465 2927 ____________________________________________ 2 [Turn over (b) B is an organic substance. Carry out the following experiments. Record your observations and deductions in the spaces provided. Identify the functional group present in B. Experiment Observations Deductions 1 (i) Add two cm3 of B to two cm3 of water in a test tube. (ii) Test the mixture with Universal Indicator paper. 2 Place 10 drops of B on a watch-glass placed on a heatproof mat and ignite using a burning splint. 3 Add one cm3 of dilute sulphuric acid to two cm3 of potassium dichromate solution. Add 10 drops of B and warm gently. Functional group present in B ___________________________________________ [25] ASC3aS7 2927 3 [Turn over 2 Titration The aim of the experiment is to determine the molarity of concentrated hydrochloric acid and its concentration in g dm 3 by titrating a diluted sample of the acid with sodium hydroxide solution. The diluted hydrochloric acid was made by adding 2.3 cm3 of concentrated hydrochloric acid to distilled water and making the solution up to 250 cm3. (a) You are provided with: diluted hydrochloric acid of unknown concentration, sodium hydroxide solution of concentration 0.1 mol dm 3, phenolphthalein indicator. You are required to: (i) titrate the sodium hydroxide against the diluted hydrochloric acid using phenolphthalein as indicator. (ii) use your results to determine the molarity of concentrated hydrochloric acid and consequently the mass of hydrochloric acid per litre. Procedure hydroxide solution diluted hydrochloric acid + phenolphthalein indicator ASC3aS7 2927 Rinse out the burette with 0.1 mol dm 3 sodium hydroxide solution. Fill the burette with 0.1 mol dm 3 sodium hydroxide solution. Rinse out the pipette with the diluted hydrochloric acid solution. Using the pipette and pipette filler, place 25.0 cm3 of the diluted hydrochloric acid solution in the conical flask. Add three drops of the phenolphthalein indicator to the conical flask and titrate with 0.1 mol dm 3 sodium hydroxide solution until the end point is reached. Record the results of one rough and two accurate titrations in the table. 4 [Turn over Results Examiner Only Marks Initial burette reading/cm3 Final burette reading/cm3 Remark Titre/cm3 Rough 1st accurate 2nd accurate Average titre ___________ cm3 [15] (b) State the colour change at the end point. From __________________ to __________________ [1] (c) (i) Write the equation for the reaction of hydrochloric acid with sodium hydroxide. ____________________________________________________ [2] (ii) Using the average titre, calculate the number of moles of sodium hydroxide used. ____________________________________________________ [1] (iii) Use the ratio in which hydrochloric acid reacts with sodium hydroxide to calculate the number of moles of hydrochloric acid present in 25.0 cm3 of the diluted acid. ____________________________________________________ [1] (iv) Calculate the number of moles of hydrochloric acid present in 2.3 cm3 of the concentrated acid. ____________________________________________________ [1] (v) Calculate the number of moles of hydrochloric acid present in 1 cm3 of the concentrated acid. ____________________________________________________ [1] ASC3aS7 2927 5 [Turn over (vi) Calculate the molarity of concentrated hydrochloric acid. Examiner Only Marks Remark ____________________________________________________ [1] (vii) Calculate the relative formula mass of hydrochloric acid. ____________________________________________________ [1] (viii) Calculate the number of grams of hydrochloric acid in 1 dm3 of concentrated hydrochloric acid. ____________________________________________________ [1] ASC3aS7 2927 6 [Turn over 3 Planning Examiner Only Marks Remark You are required to plan an experiment to identify a Group II metal, M. A suitable amount of the metal is approximately 0.3 g. If this amount of metal is added to 50 cm3 of 0.1 mol dm 3 hydrochloric acid and the volume of hydrogen collected and measured, the identity of M can be determined. The equation for the reaction is: M + 2HCl MCl2 + H2 (a) (i) Draw a labelled diagram of the apparatus which could be used to react the metal with the hydrochloric acid and to measure and collect the hydrogen produced using a syringe. [3] (ii) The metal needs to be added quickly to the apparatus without gas being lost. Suggest how this may be carried out. ____________________________________________________ [1] (iii) State two observations that could be made to show that the reaction has finished. ______________________________________________________ ____________________________________________________ [2] (iv) Suggest another way of collecting the hydrogen rather than in a syringe. ____________________________________________________ [1] (v) Explain why the hydrogen collected in the syringe is not pure. ____________________________________________________ [1] ASC3aS7 2927 7 [Turn over (b) The metal is weighed using a suitable container. State the weighings which should be made. Examiner Only Marks Remark __________________________________________________________ _______________________________________________________ [2] (c) Suppose that 0.25 g of M gave 44 cm3 of hydrogen at 20 C and one atmosphere pressure. (i) Calculate the number of grams of M that produce 1 dm3 of hydrogen. ____________________________________________________ [1] (ii) Calculate the number of grams of M that produce 24 dm3 of hydrogen. ____________________________________________________ [1] (iii) What is the relative atomic mass of M? ____________________________________________________ [1] (iv) Identify M. ____________________________________________________ [1] (d) An alternative way to determine the relative atomic mass of M would be to heat the metal hydroxide. (i) Write the equation for the reaction including state symbols. ____________________________________________________ [2] (ii) How would you determine when this reaction was complete? ______________________________________________________ ____________________________________________________ [2] (iii) State the mass measurements that should be taken to determine the value of the relative atomic mass of M using this method. ______________________________________________________ ____________________________________________________ [2] ASC3aS7 2927 8 [Turn over 4 Structured Examiner Only Marks Remark The preparation of 1-bromobutane, C4H9Br, from butan-1-ol using sodium bromide and sulphuric acid is described below. Apart from the haloalkane, sulphur dioxide and bromine are also produced. Place 30 cm3 of water, 40 g of powdered sodium bromide and 25 cm3 (21.8 g) of butan-1-ol in a 250 cm3 round-bottomed flask and fit a tap funnel to the flask. Place 25 cm3 of concentrated sulphuric acid in the funnel and slowly allow the acid to drop into the flask keeping the contents well shaken and cool occasionally in an ice-water bath. When the addition is complete replace the funnel with a reflux condenser and gently boil the mixture over a sand-bath for 45 minutes. Rearrange the apparatus for distillation and distil off the crude 1-bromobutane. Purify the distillate by first washing with water, then wash with concentrated sulphuric acid. Run off the acid layer and treat the upper layer of 1-bromobutane with sodium carbonate solution. Remove the 1-bromobutane, dry with anhydrous calcium chloride and distil through a fractionating column. Pure 1-bromobutane passes over at 99 102 C. The yield is 30.0 g. (a) Write the equation for the formation of 1-bromobutane from butan-l-ol. _______________________________________________________ [1] (b) (i) Write an equation for the formation of hydrogen bromide from sodium bromide and sulphuric acid. ____________________________________________________ [2] (ii) Explain how bromine and sulphur dioxide are formed during the preparation. ______________________________________________________ ____________________________________________________ [2] ASC3aS7 2927 9 [Turn over (c) The production of sulphur dioxide can be confirmed by a suitable chemical test. Examiner Only Marks Remark (i) Describe how you could obtain a sample of the gas. ____________________________________________________ [1] (ii) Describe a positive test for sulphur dioxide. ______________________________________________________ ____________________________________________________ [2] (d) Suggest why the concentrated sulphuric acid is added slowly and not all at once. _______________________________________________________ [1] (e) The distilled 1-bromobutane is washed with water followed by sulphuric acid and then treated with sodium carbonate solution. (i) Explain how the process of washing is carried out using a separating funnel. ______________________________________________________ ______________________________________________________ ____________________________________________________ [3] (ii) Suggest what is removed by the water. ____________________________________________________ [1] (iii)Suggest what is removed by the sodium carbonate solution. ____________________________________________________ [1] ASC3aS7 2927 10 [Turn over (f) Calculate the percentage yield using the following headings. Examiner Only Marks Remark (i) Relative formula mass of butan-1-ol. ____________________________________________________ [1] (ii) Moles of butan-1-ol used. ____________________________________________________ [1] (iii) Relative formula mass of sodium bromide. ____________________________________________________ [1] (iv) Moles of sodium bromide. ____________________________________________________ [1] (v) Relative formula mass of 1-bromobutane. ____________________________________________________ [1] (vi) Percentage yield. ____________________________________________________ [1] THIS IS THE END OF THE QUESTION PAPER ASC3aS7 2927 11 [Turn over S 1/07 7-156-1 [Turn over

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Additional Info : Gce Chemistry May 2007 Assessment Unit AS 3 Module 3: Practical Examination 2
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