9647-Chemistry-JC-Prelims-Planning-Questionsn-With-Ans

9647-Chemistry-JC-Prelims-Planning-Questionsn-With-Ans -...

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Prelims 2010 Planning Question Compilation Contents ACJC PRELIMS/P2/1 ......................................................................................................................... 3 AJC PRELIMS2010/P2/1 ................................................................................................................... 7 CJC PRELIM2010/P2/1 ................................................................................................................... 10 DHS/PRELIM2010/P2/1 ................................................................................................................. 15 HCI/PRELIM2010/P2/1 .................................................................................................................. 18 IJC/PRELIM2010/P2/1 ................................................................................................................... 24 MJC/PRELIM2010/P2/1 ................................................................................................................. 26 NJC/PRELIM2010/P2/1 .................................................................................................................. 29 PJC/PRELIM2010/P2/5 .................................................................................................................. 32 RJC/PRELIM2010/P2/1 .................................................................................................................. 34 RVHS/PRELIM2010/P2/6 ............................................................................................................... 38 SRJC/PRELIM2010/P2/6 ................................................................................................................ 41 TJC/PRELIM2010/P2/1 ................................................................................................................... 44 VJC/PRELIM2010/P2/1 .................................................................................................................. 48 YJC/PRELIM2010/P2/1 ................................................................................................................... 50 A-PDF Merger DEMO : Purchase from www.A-PDF.com to remove the watermark
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3 ACJC PRELIMS/P2/1 Weak organic acids such as tartaric acid, malic acid, lactic acid, acetic acid and citric acid, are significant constituents in determining the sensory properties of wines and beverages. Soft drinks often contain varying quantities of several acids, which give sodas their tart flavour. Acids can be classified as monobasic, dibasic, or tribasic, depending on how many protons donated to the base during neutralization. (a) A standard aqueous NaOH solution may be prepared using solid NaOH so that it can be titrated with citric acid. Suggest an appropriate concentration of the standard aqueous NaOH solution to be prepared. Show your working. [You are to assume that the pipette provided has a capacity of 25.0 cm 3 and that 10.00 cm 3 titre values 35.00 cm 3 ] In sodas such as Sprite and 7-Up, the acids are carbonic acid (from carbonated water) and citric acid. Citric acid, C 6 H 8 O 7 , reacts with NaOH(aq) in one of the following ways: C 6 H 8 O 7 (aq) + NaOH(aq) NaC 6 H 7 O 7 (aq) + H 2 O( l ) C 6 H 8 O 7 (aq) + 2NaOH(aq) Na 2 C 6 H 6 O 7 (aq) + 2H 2 O( l ) C 6 H 8 O 7 (aq) + 3NaOH(aq) Na 3 C 6 H 5 O 7 (aq) + 3H 2 O( l ) You are to plan a titration to determine which of the above equations correctly represents the neutralisation between citric acid and NaOH.
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4 [2] (b) Outline, step by step, how you would prepare, in a graduated flask, 250 cm 3 of an aqueous solution of NaOH with exactly the concentration you have given in (a) . [A r : Na,23.0; H,1.0; O,16.0]
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5 [4] (c) Draw a labelled diagram of the apparatus you would use to titrate the citric acid in 7-Up with the standard aqueous NaOH solution which you have prepared. The following details should be included in your labels: the volume of citric acid used name and capacity of apparatus used. [1] (d) Suggest a suitable indicator to be used during this titration and state the colour change observed at end-point of the titration. [1] (e) Draw up tables with appropriate headings to show the data you would record in (b) and (c) .
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6 [1] (f) Assuming that the average titre of NaOH used is y.00 cm 3 , show how you would process the results to find the correct equation for the neutralisation reaction between citric acid and NaOH. [1] (g) If the result shows that citric acid is tribasic and given the following informations: citric acid is a tertiary alcohol, citric acid is optically inactive, draw a possible structural formula of citric acid.
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