2023 CJC H2 Chem Prelims P2 QP

[Turn over 9729/2 CJC JC2 Preliminary Examination 2023 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/02 Paper 2 Structured Questions 28 August 2023 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. 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. This document consists of 19 printed pages and 1 blank page. For Examiner’s Use Paper 1 30 Paper 2 Q1 /13 Q2 /12 Q3 /14 Q4 /14 Q5 /10 Q6 /12 75 Paper 3 80 Paper 4 55 OVERALL (100%) GRADE Catholic Junior College JC2 Preliminary Examination Higher 2

2 9729/2 CJC JC2 Preliminary Examination 2023 1 (a) Nitrogen and phosphorus are elements of Group 15 in the Periodic Table. (i) Explain why phosphorus has a larger atomic radius than nitrogen. ……………………………………………………………………………………….....……… ……………………………………………………………………………………….....……… ……………………………………………………………………………………….....……… ……………………………………………………………………………………….....……… ……………………………………………………………………………………………......[2] (ii) Nitrogen exists naturally as gaseous diatomic N≡N molecules whereas phosphorus is a solid and exists as P4 molecules comprising P–P single bonds. Suggest why phosphorus does not occur naturally as P≡P molecules. …….…………………………………………………………………………………………… ….……………………………………………………………………………………………... ………………………………………………………………………………………………[1] (b) Nitrate, NO 3–, and phosphate, PO 43–, are oxoanions of nitrogen and phosphorous respectively. (i) Draw dot–and–cross diagrams to show the bonding in NO 3– and PO43– ions. Hence, suggest the shape of each of these ions. [4] (ii) The 2s and 2p orbitals of nitrogen atoms can hybridise in the same way as the 2s and 2p orbitals of carbon atoms. With reference to your answer in (b)(i), state the hybridisation state of nitrogen in NO3–. ……………………………………………………………………………………………......[1] ion NO3– PO43– dot-and-cross diagram shape

3 9729/02/CJC JC2 Preliminary Examination 2023 [Turn over (iii) Table 1.1 shows the bond lengths of two nitrogen–oxygen bonds. Table 1.1 bond N–O N=O bond length (pm) 136 115 The experimental bond length of each nitrogen–oxygen bond in the nitrate ion, NO3–, is 128 pm. With reference to your answers in (b)(i) and (b)(ii), explain this observed bond length in NO3–. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… …………………………………………………………………………………………… [1] (c) A nuclear reaction is a reaction in which there is a change to an atomic nucleus. A scientist attempts to produce P15 32 synthetically using a nuclear reaction where a neutron collides with an isotope E of another element as shown in the equation below (n represents a neutron). isotope E + n → P15 32 + H1 3 Identify isotope E, showing clearly its mass number. ………………………………………………………………………………………………......[1]

4 9729/2 CJC JC2 Preliminary Examination 2023 (d) Another type of nuclear reaction is radioactive decay, which occurs spontaneously in elements with an unstable atomic nucleus. Uranium–234 is used in nuclear power generation, and emit s a constant stream of  particles, which are equivalent to Helium–4 nuclei. Iodine–131 is used in treatment for thyroid cancer. On decaying, it emits  particles, which can be considered as electrons. A small amount of Uranium –234 and Iodine–131 are separately placed in an ionisation chamber to emit a constant st ream of radiation, and the emitted particles are passed through an electric field. (i) On the diagram below, sketch the deflection path for the emitted particles in an electric field. You may label the emitted particles as  particles and  particles respectively. + – [1] (ii) A deflection of +16° was observed when a beam of  particles was passed through an electric field. In another experiment, a beam of doubly charged X particles was passed through the electric field under the same experimental conditions. The angle of deflection was found to be –4°. Suggest the identity of ion X. Show your working. [2] [Total: 13] Ionisation Chamber Emitted particles from 234U and 131I

5 9729/02/CJC JC2 Preliminary Examination 2023 [Turn over 2 (a) Sulfanilamide is an antibiotic used to treat streptococcal infections. (i) Explain why sulfanilamide is soluble in dilute HCl. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… ….………………………………………………………………………………………[2] (ii) In sulfanilamide, the carbon atoms are sp 2 hybridised. Draw a labelled diagram to show the orbitals overlapping between any two carbon atoms in sulfanilamide. [2]

6 9729/2 CJC JC2 Preliminary Examination 2023 (iii) A 0.3 g sample containing sulfanilamide (Mr of 172.1) was dissolved and diluted to 100 cm3. A 20 cm3 aliquot was used to react with 1.33 x 10–3 mol Br2 (which was in excess) to form Y. KI was then added to react with any remaining unreacted Br2. The liberated iodine was subsequently titrated with 15.70 cm3 of 0.1 mol dm –3 sodium thiosulfate as shown in the equations below. Br2 + 2I– → 2Br – + I2 I2 + 2S2O3 2– → 2S4O6 2– + 2I– Calculate the percentage by mass of sulfanilamide in the sample. [4]

7 9729/02/CJC JC2 Preliminary Examination 2023 [Turn over (b) (i) Describe the reaction of SO3 with water. Include the approximate pH value of any resulting solution, and write an equation for any reaction that occurs. …………………………………………………………………………………………… ..………………………………………………………………………………………….. ….………………………………………………………………………………………[2] (ii) Write the electronic configuration of sulfur. ….………………………………………………………………………………………[1] (iii) Explain why sulfur has a lower first ionisation energy than phosphorus. …………………………………………………………………………………………… ..………………………………………………………………………………………….. ….………………………………………………………………………………………[1] [Total: 12]

8 9729/2 CJC JC2 Preliminary Examination 2023 3 Wine contains varying concentrations of different acids , and the amount of acids is influenced by factors such as climate and the fermentation process of grapes that make the wine. The principal acid present in grapes is tartaric acid, which gives wine the tart taste. (a) In an experiment to determine the tartaric acid content of a 750 cm 3 bottle of white wine, a titration was carried out and 17.60 cm 3 of 0.01 mol dm -3 N