RVHS Prelim P2 QP

River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION (II) CANDIDATE NAME 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.

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3 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II 1 Heavy metals, in the form of soluble ions, are common contaminants of industrial wastewaters. Due to their toxicity, they are typically removed prior to wastewater discharge. The heavy metal contents of wastewaters can be effectively removed to acceptable levels by precipitating the metal in an insoluble form. (a) Each of the sample solution s, P and Q, contains a type o f heavy metal ion. The ion is either silver(I) or zinc. The following shows the results of a chemical test on lead( II) ions and the two unknown samples. Test P Q Lead(II) ion To 1 cm3 of sample in a test-tube, add potassium chloride solution, followed by excess aqueous ammonia. No precipitate formed. White ppt formed is soluble in excess aqueous ammonia. White ppt formed is insoluble in excess aqueous ammonia. (i) Write an equation, with state symbols, for the reaction involving lead(II) ion. ……………………………………………………………………………... [1] (ii) Deduce the identity of ion Q and explain the observations reported. Q: ………………………………………………….. Explanation: ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ……………………………………………………………………………... [2]

4 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II (ii) Suggest a chemical test to confirm the identity of P. Describe the expected observation. Chemical Test: ………………………………………………………………………………… ………………………………………………………………………………… …………………………………………………………………………………. Observation: ………………………………………………………………………………… ………………………………………………………………………………… ……………………………………………………………………………... [2] (b) The wastewater from a metal smelter contains high level of lead( II) ions. It is also likely to contain some silver(I) ion and zinc ions. The concentration of lead( II) ion in the wastewater can be determined using precipitation gravimetric method. Prior to the experiment, pre-concentration is carried out on the wastewater to increase the concentration of lead( II) ions in the sample. Then, suitable reagents are selected to selectively precipitate lead(II) ions from the concentrated sample solution. The concentra tion of lead(II) ions in the original sample can be calculated from the mass of this precipitate. Using all the information provided, plan a precipitation gravimetric experiment to determine the concentration of lead(II) ions in untreated waste sample. You are given the use of common laboratory apparatus and the following chemicals. Chemicals:  10 cm 3 of aqueous sample obtained by pre -concentrating 5 dm 3 of wastewater.  0.10 mol dm3 aqueous potassium chloride  Any other common reagents in the laboratory at 1.0 mol dm3 A preliminary calculation shows that about 9 cm3 of potassium chloride solution is required for precipitation. Your plan should include details of:  how an accurate mass of the precipitate containing lead(II) can be obtained;  how you would check that all lead(II) ions are precipitated.

5 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………………... [5] (c) (i) Given that the mass of PbC l2 obtained is 0.102 g. Calculate the concentration of lead(II) ions in untreated wastewater. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………………... [2] [Total: 12]

6 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II 2 Compounds with a giant ionic structure usually have high melting points. However, scientists have developed low melting point ionic compounds which are liquids at room temperature. An example of this would be: 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM+ PF6 ) [ ][PF6] (a) Draw a suitable diagram to illustrate the shape of the hexafluorophosphate anion. Suggest a value for the bond angle. [2] (b) BMIM+PF6  has a melting point of 8 C. In comparision, NaCl has a melting point of 801 C. In terms of structure and bonding, explain the difference in melting points between both compounds. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………................................................... ........................................................................................................................... ........................................................................................................................... ...................................................................................................................... [2]

7 River Valley High School 9647/02/PRELIM/15 2015 Preliminary Examination II (c) Imidazole is used in the manufacture of the ionic liquid BMIM+PF6 . Imidazole can be considered as a monoprotic weak base with pKb value of 6.95. (i) Explain what is meant by the term pKb as applied to a weak base B. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ……………………………………………………………………………... [2] (ii) Calculate the pH of a solution when 25 cm 3 of 0.100 mol dm 3 of imidazole is mixed with 20 cm3 of 0.125 of mol dm3 HNO3. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ……………………………………………………………………………........ ................................................................................................................ ................................................................................................................ ................................................................................................................ ................................................................................................................ ................................