TJC_H2_CHEM_P2_QN Prelim

1 9647/02/TJC Prelim 2014 [Turn Over For Examiner’s Use s CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9647/02 Paper 2 Structured Questions 29th August 2014 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 22 printed pages. For Examiner’s Use 1 /12 2 / 8 3 /10 4 /16 5 /10 6 /16 Total PRELIMINARY EXAMINATIONS HIGHER 2

2 9647/02/TJC Prelim 2014 [Turn Over For Examiner’s Use 1 Planning (P) Chromatography is used to separate mixtures of substances into their components. The components move at different speeds when they ar e carried by a liquid or a gas called the “mobile phase” over an adsorbent material, called the “stationary phase”. (a) A quick and convenient method of chromatographic a nalysis for organic compounds is thin- layer chromatography (TLC). The stationary phase is silica gel which is coated onto sheets of glass, and the sheets are cut into thin strips. A solution of a mixture of two organic compounds to be analysed is spotted near the bottom of the plate. The plate is then stood in a closed jar which is saturated with an appropriate solvent as the mobile phase. The reason for covering the jar is to make sure that the atmosphere in the beaker is saturated with solvent vapour. As the solvent travels up the plate by capillary action, the components of the mixture travel upwards at different rates and thus separate. The solvent is allowed to rise until it almost reaches the top of the plate (indicated by the solvent front), giving a maximum separation of the mixture components. The TLC plate is then removed from the jar for further analysis. Figure 1: TLC analysing a solution of a mixture of two organic compounds (i) A pencil line is drawn near the bottom of the TLC plate. Suggest a reason why any labeling on the TLC plate has to be drawn in pencil and not in ink. Cover Solvent front Solvent (0.