SRJC H1 CHEM P2 QP

1 SRJC 8872 / 02 / JC2 Prelims/ 2015 SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME CLASS CHEMISTRY 8872/02 JC 2 Preliminary examination 20 August 2015 Paper 2 2 hours Additional Materials: Data Booklet Writing paper READ THESE INSTRUCTIONS FIRST Candidates answer on the question paper. Write your name and class on all the work you hand in. Write in dark or blue pen. Do not use paper clips, glue or correction fluid. The number of marks is given in bracket [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This document consists of 13 printed pages and 3 blank page. FOR EXAMINER’S USE P1 (MCQ) 30 P2 A1 8 A2 9 A3 16 A4 7 B5 20 B6 20 B7 20 Total 110

2 SRJC 8872 / 02 / JC2 Prelims/ 2015 Section A Answer all the questions in the spaces provided. 1 Elements A, B, C, D and E are five consecutive elements from Period 3 and 4 of the Periodic Table. The following shows the successive ionisation energies of element C. No. of electrons removed 1 2 3 4 5 6 7 8 Ionisation energy / kJ mol–1 1260 2300 3850 5150 6542 9362 11018 33604 (a) (i) Deduce and explain which group element C belongs to. ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………......................... ………………………………………………………………………………......................... (ii) Hence, state the identity of element C and write down its electronic configuration. ………………………………………………………………………………………………… ………………………………………………………………………………………………… [4] (b) Explain the following observations, giving equations where appropriate. (i) The first ionisation energy of element B is lower than the first ionisation energy of element A. ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… For Examiner’s use

3 SRJC 8872 / 02 / JC2 Prelims/ 2015 (ii) A strongly acidic solution is formed when the chloride of A reacts with water. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… [4] [Total: 8] For Examiner’s use For Examiner’s use

4 SRJC 8872 / 02 / JC2 Prelims/ 2015 2 A sequence of reactions is shown below. v (a) In the appropriate boxes draw the structures of compound F, G, H, J and K. (b) For the reaction in the scheme shown above state (i) the reagents and conditions for reactions II and III, Reaction II: ……………………………………………….. Reaction III: ……………………………………..……….. (ii) the type of reaction for reactions I and III. Reaction I: ………………………………………………..... Reaction III: ……………………………………………….. [Total: 9] F J KMnO4, H+, heat II I2(aq) + NaOH(aq) heat I HCN + NaCN, cold III For Examiner’s use G, C6H10O2 H K

5 SRJC 8872 / 02 / JC2 Prelims/ 2015 3 Aldehydes are commonly used to produce resins to make plastics and adhesives. It exists in equilibrium with its isomer, enol through a process called enolization. The reaction involves the transfer of one proton and the shift of the double bond. An example of enolization of acetaldehyde is shown below. ∆H ɵ rxn > 0 acetylacetaldehyde enol (a) (i) Write an expression for the equilibrium constant, Kc, for this reaction. (ii) It was found that 76% of acetylacetaldehyde exist as an enol when dissolved in water. Calculate the equilibrium constant, Kc, for this reaction. (iii) Explain the significance of this value on the equilibrium position and the relative concentrations of the two species present at equilibrium. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… For Examiner’s use

6 SRJC 8872 / 02 / JC2 Prelims/ 2015 (iv) Suggest what will happen to the composition of the equilibrium mixture when the system is heated. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... [6] (b) Acetylacetaldehyde can undergo oxidation with potassium dichromate (VI) under heat to form a carboxylic acid. (i) Write two redox half-equations to represent the reaction between acetylacetaldehyde and Cr2O7 2– ions and prove that the overall equation is as follows: 3CH3COCH2CHO + Cr2O7 2– + 8H+  3CH3COCH2COOH + 4H2O + 2Cr3+ (ii) 8 cm 3 of liquid acetylacetaldehyde was dissolved in water and made up to 250 cm 3. 25.0 cm 3 of this solution was titrated with 0.10 mol dm –3 acidified potassium dichromate(VI). Given that the density of acetylacetaldehyde is 0.956 g cm –3, calculate the volume of potassium dichromate(VI) required to complete the titration. For Examiner’s use

7 SRJC 8872 / 02 / JC2 Prelims/ 2015 (iii) Propose a simple chemical test that allows you to confir m the presence of acetylacetaldehyde and state any observations clearly. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… [6] (c) (i) Deduce which of the two acids, CH 3COCH2COOH or CH 3COCHClCOOH, has a higher pKa value. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………......................... (ii) Propose a simple test -tube test which can be achieved in the school laboratory to differentiate CH3COCH2COOH from CH3COCHClCOOH. ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………......................... ………………………………………………………………………………………………… [4] [Total: 16] For Examiner’s use

8 SRJC 8872 / 02 / JC2 Prelims/ 2015 4 Aluminium reacts with fluorine, chlorine and oxygen to for m aluminium fluoride, aluminium chloride and aluminium oxide respectively. (a) Using chemical equations only, explain