EJC 2026 Prelim P3 Ans

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2026 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 5 – INDEX NUMBER CHEMISTRY Paper 3 Structured Questions 9476/03 14 September 2026 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Section A: answer all questions. Section B: answer one question. Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. Write and shade your index number in the box provided at the top of the page. Write your answer to each question in the space provided. Do not use an erasable pen. Do not use correction fluid or tape. The use of an approved scientific calculator is expected, where appropriate. The total mark for this paper is 75. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 3 A1 / 19 A2 / 19 A3 / 17 B4 or 5 / 20 Total / 75 This document consists of 25 printed pages and 3 blank pages.

2 © EJC 9476/03/J2PRELIM/26 Section A Answer all the questions from this section in the spaces provided. 1 Copper is a transition element that forms a rich variety of compounds with varying oxidation states. Fehling’s solution comprises Cu2+ complexed with tartrate ligands in an alkaline medium, forming a dark blue complex. (a) (i) Explain what is meant by the term transition element. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [1] (ii) Describe the appearance of a positive result of a test using Fehling’s solution. ................................ ................................ ................................ ................................ . [1] (b) Poly(2-hydroxyethyl methacrylate), or pHEMA, is a highly absorbent polymer used to manufacture soft contact lenses. The polymerisation process used to form pHEMA from its monomers is often catalysed by a Cu+ complex. A section of the pHEMA polymer chain is shown. (i) Draw the structure of the monomer used to form pHEMA. [1] (ii) With reference to the structure of pHEMA and your answer in (b)(i), state the type of polymerisation involved in its formation and explain your reasoning. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [2] A transition element (or transition metal) is a d block element whose atom has an incomplete d subshell or which can give rise to stable cations with an incomplete d subshell. Addition polymerization. The polymer chain consists of a continuous carbon-carbon single bond backbone / The polymer chain is formed by the breaking of C=C  bonds in the monomers / The polymer chain is formed without the elimination of any small molecules / The molecular mass of the polymer is a multiple of its monomer. Appearance of reddish brown/ brick-red / red ppt of Cu2O.

3 © EJC 9476/03/J2PRELIM/26 [Turn over (iii) Explain why the Cu2+ complex in Fehling’s solution is coloured , whereas the Cu+ complex used as the catalyst is colourless. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [4] (c) Cu2+(aq) and Cu+(aq) are catalysts involved in the oxidation of ascorbic acid, C6H8O6. C6H8O6(aq) + ½O2(aq) ⎯⎯⎯⎯⎯⎯⎯⎯ → 2+ +Cu / Cu (aq) C6H6O6(aq) + H2O(l) The uncatalysed reaction is very slow due to its high activation energy. (i) State and explain the type of catalysis in the reaction. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [1] (ii) Propose a two-step process to show how Cu2+(aq) catalyses the reaction. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [2] Homogeneous catalysis. The reactants and the catalyst are in the same phase/ state. 2+ + + 6 8 6 6 6 6 + + 2+ 22 Step 1: C H O (aq) + 2Cu (aq) C H O (aq) + 2Cu (a q)+ 2H (aq) Step 2: ½O (aq) + 2Cu + 2H (aq) H O(l) + 2Cu (aq) ⎯⎯→ ⎯⎯→ Cu2+ has a partially-filled 3d subshell . In the presence of tartrate ligands, the 3d orbitals of Cu2+ splits into two different energy levels. A 3d electron in the lower energy d orbital absorbs light energy from the visible spectrum, and is promoted to a higher energy d orbital. The remaining wavelengths are transmitted and the complementary dark blue colour is observed. Cu+ has a fully filled 3d subshell, meaning no d-d transition can occur. Hence the complexes appear colourless.

4 © EJC 9476/03/J2PRELIM/26 (d) Ascorbic acid does not contain a carboxylic acid functional group. Instead, it is classified as a weak acid because of a unique structural arrangement known as an ene -diol group adjacent to a carbonyl group. The ene-diol group consists of C=C where both carbon atoms are directly attached to –OH groups. In an aqueous medium, one of these specific ene -diol –OH groups can readily donate a proton, H+, to a water molecule, acting as a Brønsted-Lowry acid. Figure 1.1 (i) Using the resonance structures of the conjugate bases shown in Figure 1.1, explain why Ha is more acidic than Hb. ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ ..... ................................ ................................ ................................ ................................ . [1] (ii)