H1 Chemistry Prelim P2 QP ACJC

This document consists of 19 printed pages and 1 blank page. Anglo-Chinese Junior College JC2 Preliminary Examination Higher 1 CANDIDATE NAME FORM CLASS TUTORIAL CLASS 2CHX _ _ INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 27 Aug 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name and index number in the spaces on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer one question. The use of approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners’ use only Section A 1 / 13 2 / 7 3 / 10 4 / 7 5 / 13 6 / 10 Section B 7 or 8 / 20 Total / 80

2 ACJC 2025 8873/02/2025 Section A Answer all questions in this section in the spaces provided. 1 In the presence of an acid catalyst, ethanal reacts with methanol to form 1,1-dimethoxyethane. CH3CHO(l) + 2CH3OH(l) ⇌ CH3CH(OCH3)2(l) + H2O(l) ethanal methanol 1,1-dimethoxyethane (a) 0.20 mol dm−3 of ethanal and 0.1 mol dm−3 of methanol were placed in a reaction vessel. Strong acid was then added as a catalyst. It was found that the equilibrium mixture contained 0.025 mol dm−3 of 1,1-dimethoxyethane. Calculate the equilibrium concentrations of the other reactants and products. [3] (b) Write the expression for the equilibrium constant for this reaction, Kc, stating its units. [2] (c) Use your answers in (a) to calculate the value of Kc. [1] H+

3 ACJC 2025 8873/02/2025 [Turn over (d) 2-methylprop-2-enoic acid can be obtained from 2-methylprop-2-en-1-ol. (i) To prevent the C=C bond from reacting in other reactions, reaction 1 is first carried out. Draw the structure of A. [1] (ii) Suggest the reagent used in reaction 1. ……………………………………………………………………………………...….[1] (iii) Name the type of reaction in reactions 2 and 3. reaction 2: …………………… reaction 3: …………………… [2] (iv) Draw the displayed formula of 2-methylprop-2-enoic acid. [1] (v) Suggest a chemical test to distinguish between 2-methylprop-2-en-1-ol and B. State the observations. ……………………………………………………………………………………………. ……………………………………………………………………………………….…[2] [Total: 13] 2-methylprop-2-enoic acid reaction 1 C4H9BrO reaction 2 reaction 3 2-methylprop-2-en-1-ol A A B

4 ACJC 2025 8873/02/2025 2 (a) Sodium polyacrylate is a superabsorbent polymer that can absorb and retain large amounts of water relative to its own mass. It is widely used in diapers. (i) Draw the monomer used to make sodium polyacrylate. [1] (ii) Explain why this polymer is an addition polymer. …………………………………………………………………………………….……… ………………………………………………………………………………………….[2] (iii) Using the information provided above, explain, in terms of structure and bonding, the property of this hydrogel. …………………………………………………………………………………………… …………………………………………………………………………………………[1] (iv) In an experiment, 4.0 × 10−6 mol of polymer absorbed 150 g of water. This mass of water is 300 times the mass of polymer used. Calculate the relative molecular mass of the polymer. [1]

5 ACJC 2025 8873/02/2025 [Turn over (v) After polymerisation, sodium polyacrylate is further processed to form crosslinked sodium polyacrylate found in commercial products. The following diagram shows the structure of crosslinked sodium polyacrylate. Explain how crosslinking of sodium polyacrylate allows it to remain as a solid mass in wet diapers. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ………………………………………………………………………………………….[2] [Total: 7]

6 ACJC 2025 8873/02/2025 3 (a) The noble gas xenon was once thought to be inert. It has since been discovered that xenon will react with strong oxidants. For example, xenon reacts with fluorine gas, forming a series of fluorides, XeF2, XeF4 and XeF6. (i) Draw dot-and-cross diagram of xenon difluoride and state its bond angle. [2] (ii) Name the shape of xenon difluoride. ………………………………………………………………………………………….………………….[1] (iii) Explain the three-dimensional arrangement using the principles of the VSEPR theory. ………………………………………………………………………………...………….. ………………………………………………………………………………...………….. ……………………………………………………………………………………...….[2] (b) The boiling points of some fluoride compounds are shown in Table 3.1. Table 3.1 Explain the difference in boiling points using structure and bonding. compound Mr boiling point/ oC CF4 88 −127.8 ClF3 92.5 11.8 PF3 88 −101.8 …………………………………………………...…………………………………...………….. …………………………………………………...…………………………………...………….. ……………………………………………………………………………………………...….[3] (c) Explain why the ionic bond in lithium iodide, LiI, has greater covalent character than that of lithium fluoride, LiF. …………………………………………………...…………………………………...………….. …………………………………………………...…………………………………...………….. ……………………………………………………………………………………………...….[2] [Total: 10]

7 ACJC 2025 8873/02/2025 [Turn over 4 The first ionisation energy of some consecutive elements in periods 2 and 3 are plotted. (a) Explain why the first ionisation energy of element A is much higher than that of element B. …………………………………………………...…………………………………...………….. …………………………………………………...…………………………………...………….. ……………………………………………………………………………………………...….[1] (b) Write an equation to represent the second ionisation energy of element A. ……………………………………………………………………………………………...….[1] (c) Explain the increasing trend of the first ionisation energies from element B to G. …………………………………………………...…………………………………...………….. …………………………………………………...…………………………………...………….. ……………………………………………………………………………………………...….[2] (d) State which element is sulfur and explain your answer. …………………………………………………………………………………………………… ……………………………………………………………………………………………...….[2] (e) State the number of occupied principal quantum shells in one atom of sulfur in its ground state. ……………………………………………………………………………………………...….[1] [Total: 7] first I.E. / kJ mol-1 A B C D E F G

8 ACJC 2025 8873/02/2025 5 (a) A student determine d the concentration of ethanoic acid, CH 3COOH in a bottle of kitchen vinegar. He add ed 10 cm 3 of vinegar to a volumetric flask and followed by deionised water to make up the solution to 250 cm3. The diluted vinegar was then poured into the burette. On titration, 25 cm3 of 0.0450 mol dm−3 Ba(OH)2 was exactly neutralised by 25.45 cm3 of the diluted vinegar. (i) Write the balanced equation between CH3COOH and Ba(OH)2. ………………………………………………………………………………………….[1] (ii) Calculate the amount of CH3COOH neutralised.