Prelim Paper 2 - Question Paper ACJC H2 Chem

1 ACJC2025 9729/02/Prelim/2025 [Turn over Anglo-Chinese Junior College JC2 Preliminary Examinations Higher 2 CANDIDATE NAME FORM CLASS TUTORIAL CLASS INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 27 August 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your index number and name in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners’ use only 1 / 7 2 / 12 3 / 10 4 / 11 5 / 11 6 / 16 7 / 8 Total / 75 This document consists of 24 printed pages.

2 ACJC2025 9729/02/Prelim/2025 [Turn over Answer all questions in the spaces provided. 1 When ammonium dichromate( VI) is added gradually to molten ammonium thiocyanate, Reinecke’s salt is formed. It has the formula NH 4[Cr(SCN)x(NH3)y] and the following composition by mass: Cr 15.5 %; S 38.15 %; N 29.2 %. (a) Calculate the values of x and y in the above formula. [2] (b) Suggest a shape for the complex anion. …………………………………………………………………………………………………...[1] (c) Draw two possible structures for the anion and state the type of isomerism it exhibits. …………………………………………………………………………………………………...[2]

3 ACJC2025 9729/02/Prelim/2025 [Turn over (d) Linkage isomerism is a form of constitutional isomerism in which certain coordination compounds have the same composition but differ in which atom of the ligand is bonded to the metal. Examples of linkage isomers are violet-colored [(NH3)5Co-SCN]2+ (S being the donor atom) and the orange [(NH3)5Co-NCS]2+ (N being the donor atom). Draw the dot -and-cross diagrams of NCS ˉ and SCNˉ. In each diagram, underline the donor atom. [2] [Total: 7]

4 ACJC2025 9729/02/Prelim/2025 [Turn over 2 (a) X can be converted to Y via three steps as shown in the reaction scheme below. (i) There are two isomers possible for P. Draw the structure of P that will eventually lead on to Y. [1] (ii) Explain if your answer in (a)(i) is the major product. ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ………………………………………………………………………………………….. [2] (iii) Draw the structure of Q. State the reagents and conditions to synthesise Q from P. reagents & conditions …………………………………………………………….…..[2] A A Q P

5 ACJC2025 9729/02/Prelim/2025 [Turn over (b) (i) G has the molecular formula, C8H14. Treating G with hydrogen in the presence of Ni, yields H, with the molecular formula, C 8H16. Upon mild oxidation, G gives a tertiary diol, J. Upon vigorous oxidation G gives a diketone, K, which reacts with aqueous alkaline iodine to produce hexanedioic acid upon acidification. Draw the structures of G, H, J and K. [4] A AA AA AA G H J K

6 ACJC2025 9729/02/Prelim/2025 [Turn over (ii) L is an isomer of G. Treating L with hydrogen in the presence of Ni, yields W, with the molecular formula, C 8H18. It undergoes vigorous oxidation to give propanone as the only organic product in addition to CO2. Deduce the structure of L with reasoning. ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... …………………………………………………………………………………………..[3] [Total: 12] L

7 ACJC2025 9729/02/Prelim/2025 [Turn over 3 (a) At the time of its discovery by Scottish chemist Sir William Ramsay, the noble gas xenon was considered 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) The structure of xenon tetrafluoride has six electron pairs on xenon and therefore the structure is based on an octahedral configuration as shown below. On Fig. 3.1, draw the two possible three-dimensional arrangements of the electron pairs on xenon in xenon tetrafluoride and tick the one observed, that gives the molecule its shape, explaining your choice with appropriate reasoning based on the principles of the VSEPR theory. Fig. 3.1 ……………………………………………………………………………………………... ……………………………………………………………………………………………... ……………………………………………………………………………………………... …………………………………………………………………………………………..[2]

8 ACJC2025 9729/02/Prelim/2025 [Turn over (ii) The structure of xenon difluoride has five electron pairs on xenon and therefore the structure is based on a trigonal bipyramidal configuration as shown below. On Fig. 3.2, draw the three possible three-dimensional arrangements of the five electron pairs on xenon in xenon difluoride and tick the one observed, that gives the molecule its shape, explaining your choice with appropriate reasoning based on the principles of the VSEPR theory. Fig. 3.2 …………………………………………………………………………………………...... …………………………………………………………………………………………...... ……………………………………………………………………………………………... ………………………………………………………………………………………….. [3]

9 ACJC2025 9729/02/Prelim/2025 [Turn over (b) The kinetics of the formation of xenon difluoride from xenon and fluorine has been studied under various conditions. At 120 °C, the rate equation for the formation of XeF 2 is found to be first order with respect to Xe and zero order with respect to F2. (i) Write the rate equation for the formation of XeF2 and suggest the units for the rate constant. [2] (ii) The Arrhenius equation describes the relationship between the rate constant and temperature. e aE RTkA − = The uncatalysed reaction between xenon and fluorine to form XeF 2 at a temperature T has a rate constant k, with collision frequency factor A and activation energy, Ea. When a nickel difluoride catalyst is added to the reaction mixture, the rate constant changes to kcat, with a different collision frequency Acat and a different activation energy, Ecat. It is found that the catalysed reaction is 13 times faster at 120 °C and 23 times faster at 100 °C. The change in activation energy, ΔE = Ea − Ecat. Assuming that the collision frequency factors do not depend on temperature, write an expression for the ratio kcat/k in terms of T, ΔE and any