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. ……………………………………………………...……………………………………... .……………………………………………………...…………………………………….. …………………………………………………………………………………………….. [2]

NJC/H2 Chem Preliminary Examination/02/2022 4 (d) Indium and aluminium are elements in Group 13 of the Periodic Table. Indium has very similar chemical properties to aluminium. ● Indium reacts vigorously with hydrochloric acid to form a colourless gas and a soluble salt. ● Indium oxide, In2O3, is amphoteric. In2O3 is a white solid which dissolves in excess aqueous NaOH. ● Gaseous indium bromide, In2Br6, contains coordinate bonds. (i) Identify the formula of the salt formed when indium reacts with hydrochloric acid. ………………………………………… [1] (ii) Construct an equation for the reaction of In2O3 with excess aqueous NaOH. ………………………………………………………………………..…………………… [1] (iii) Draw a diagram that clearly shows the types of bonds in a molecule of In2Br6 (g). [1]

NJC/H2 Chem Preliminary Examination/02/2022 5 [Turn over (e) In the periodic table, e lement Y is above element Z in the same group. Elements Y and Z are subjected to a series of reactions in the flowchart below. (i) Calculate the value of n in ZCln. [1] (ii) Suggest the identities of elements Y and Z and explain why YCln and ZCln react differently with water. ………………………………………………………………………..…………………… ………………………………………………………………………..…………………… ………………………………………………………………………..…………………… ………………………………………………………………………..…………………… [2] (iii) Write a balanced equation for the reaction of ZCln with water. ………………………………………………………………………..…………………… [1] [Total:15] Y 0.020 mol excess Cl2 AgCl (s) 11.54 g excess AgNO3(aq) YCln (l) 0.020 mol water two immiscible layers of water and YCln Z 0.020 mol excess Cl2 ZCln (l) 0.020 mol water filter filtrate white residue +

NJC/H2 Chem Preliminary Examination/02/2022 6 2 (a) Oil spills are hazardous as it affects the marine ecosystem, and the marine life-forms existence gets threatened. It becomes increasingly important to employ various clean up methods for tackling the menace that oil spills pose to the marine ecosystem. (i) Oil consists mainly of hydrocarbons. Sheets of sorbents , usually made of materials like polypropene, can be used to absorb oil. The structure of polypropene is given below. Structure of polypropene Sorbent sheets Suggest how sorbents are able to absorb and effectively remove oil from water. ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... [2]

NJC/H2 Chem Preliminary Examination/02/2022 7 [Turn over (ii) Another method of removing oil floating on the sea surface is to ignite and burn it off. Such burning of oil will cause an increase in temperature of the sea. One of the major components of oil is decane, C 10H22. A simulation was done where 500 g of decane floating over 200 dm3 of water was burnt off. Given that the enthalpy change of combustion of decane is −300.9 kJ mol −1, determine the rise in temperature of the body of water. [3] (iii) The actual temperature rise differs from the calculated value in (a) (ii). Suggest a reason for the discrepancy. ……………………………………………………………………………………... [1]

NJC/H2 Chem Preliminary Examination/02/2022 8 (b) Propene is the second most important starting material in the petrochemical industry. It is involved in a two -step synthesis to make a class of compounds known as epoxides. Step 1: Propene is reacted with HOCl to give two possible products, G or F. CH2 CH3 + HOCl CH3 Cl OH CH3 OH Cl or G F Step 2: The mixture of G and F is treated with Na to give the epoxide. CH3 Cl OH CH3 OH Cl or Na CH3 O + H2 G F (i) State the type of isomerism between G and F. ……………………………………………………………………………………... [1] (ii) Determine the type of reaction that occurs in each step. Step 1: …………………………..…………… Step 2: ……………………………………….. [2]

NJC/H2 Chem Preliminary Examination/02/2022 9 [Turn over (iii) Outline the mechanism for formation of F in step 1. In your answer, show any relevant charges, lone pairs of electrons and movement of electrons. [2] (iv) Hence explain why F is the major product in step 1. ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... ……………………………………………………………………………………... [2] (v) Suggest the importance of Na in t