NJC_2022_H2_Chemistry_Prelim_P2_QP

NJC/H2 Chem Preliminary Examination/02/2022 1 [Turn over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on Question Paper. Additional Materials: Data Booklet 9729/02 29 August 2022 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number 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 paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /15 2 /22 3 /15 4 /11 5 /12 Paper 2 Total /75 Marks Weightings Paper 1 /30 15% Paper 2 /75 30% Overall Percentage Paper 3 /80 35% Paper 4 /55 20% Grade This document consists of 19 printed pages and 1 blank page.

NJC/H2 Chem Preliminary Examination/02/2022 2 Answer all the questions in the spaces provided. 1 (a) Chemists have recently established that four molecules of water are required for the dissociation of a single molecule of HCl (reported in Science, 2009). Given that 1.00 dm 3 of water contains 55.6 mol of H 2O, calculate the number of molecules of hydrogen chloride, HC l, that should therefore dissociate in 1.00 dm 3 of water. [1] (b) Commercial concentrated hydrochloric acid, HCl, fumes strongly on exposure to moist air and thus is known as ‘fuming hydrochloric acid’. 1.00 cm 3 of fuming hydrochloric acid was transferred with a graduated pipette to a 100 cm3 volumetric flask. The volume wa s made up to 100 cm 3 with deionised water and the solution was labelled F. 10.0 cm 3 of solution F was neutralised by 24.75 cm 3 of 0.0500 mol dm−3 of aqueous sodium hydroxide. Calculate the concentration of HCl in the fuming hydrochloric acid in mol dm−3. [2]

NJC/H2 Chem Preliminary Examination/02/2022 3 [Turn over (c) (i) The halide ions, X – (where X = Cl, Br, I), show clear trends in their physical and chemical properties. State and explain the relative thermal stabilities of the hydrogen halides, HX. ………………………………………………………………………………………...…... …………………………………………………………………………………..………... [2] The bar chart below shows the boiling points of HC l, HBr and H I. The boiling point of HF is not shown. (ii) Explain why HI has a higher boiling point than HCl and HBr. ……………………………………………………...…………………………………….. ……………………………………………………...……………………………………... …………………………………………………………………………………………….. [1] (iii) Complete the bar chart above to show the boiling point of HF. Explain your answer. ……………………………………………………...……………………………………... .……………………………………………………...…………