RVHS Prelim P2_Student_ANS

River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION (II) CANDIDATE NAME Suggested Solutions CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 14 September 2015 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of 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 in the space provided. A Data Booklet is provided. Do NOT write anything on it. 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. For Examiner’s Use Paper 2 Question Number 1 2 3 4 5 6 Total Marks 12 14 14 8 9 15 72 Paper 1 40 Paper 3 80 Total 192 This document consists of 20 printed pages.

2 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II 1 (a) (i) Pb2+(aq) + 2Cl (aq) PbCl2(s) [1] (ii) Q: silver(I) ion Explanation: Ag+ (aq) forms a white, insoluble/sparingly soluble salt, AgCl, with Cl(aq). AgCl (s)  Ag+(aq) +Cl (aq) ----(1) [Ag+] decreases as Ag+ reacts with NH3(aq) forming a colourless complex, [Ag(NH3)2]+(aq). Equilibrium position of (1) shifts to the right and thus AgCl dissolves [2] (ii) Chemical Test: To 1 cm 3 of sample in a test -tube, NaOH(aq), dropwise follow by excess. Expected observation: White ppt formed is soluble in excess NaOH(aq) to give a colourless solution. Reject: Aq NH3 because it is one of the reagents used in a(i) [2] (b) 1. Place the 10 cm 3 of aqueous sample provided in a clean 100 cm3 beaker. 2. Using a 10 cm 3 measuring cylinder , add 10 cm 3 of 0.10 mol dm -3 potassium chloride solution . Stir well to ensure complete precipitation. 3. Using a 10 cm 3 measuring cylinder, add 10 cm3 (accept 2 cm3, i.e. 20 times of nCl - used, to 10 cm 3 ) of 1.0 mol dm -3 aqueous ammonia. Stir well to ensure any AgC l precipitated will dissolve. 4. Filter the mixture into a clean 100 cm3 conical flask, and collect the insoluble white precipitate of PbCl2 as residue. 5. To the filtrate in the conical flask, add a dropper full of aqueous potassium chloride to check if there is Pb 2+ remaining in the solution. If white ppt is formed, repeat steps 2 to 4. 6. With the ppt still on the filtration setup, use deionized water to wash the ppt and discard the washings. 7. Weigh a clean crucible/boiling tube/small beaker. Transfer quantitatively all the ppt into this crucible/boiling tube/small beaker. 8. Dry the ppt by using infrared lamp/ov