CJC 2022 JC2 H2 Chem Prelim P2 QP 0909

[Turn over 9729/2 CJC JC2 Preliminary Examination 2022 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/02 Paper 2 Structured Questions 26 August 2022 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 calculation 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 /11 Q3 /15 Q4 /12 Q5 /11 Q6 /13 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 2022 1 (a) Fehling’s solution is used in Qualitative Analysis of organic compounds. It is prepared fresh by mixing a solution of CuSO4 (Fehling’s A solution) with a mixture of tartrate ions and NaOH (Fehling’s B solution). When the two solutions are mixed, the tartrate ions act as ligands to form a complex ion with the Cu2+ ions. (i) Another reagent with similar action to Fehling’s solution is Benedict’s solution, which is also an alkaline solution of Cu2+, but the ligand forming the complex ion is citrate ion instead of tartrate ion. Suggest why the presence of the ligand is necessary in Fehling’s (and Benedict’s) solution. …………………………………………………………………………………………… …………………………………………………………………………………………… ….………………………………………………………………………………………[1] Fehling’s solution was used to distinguish between three unknown compounds, A, B and C: Compound Observation with Fehling’s solution A blue solution B red ppt C blue solution It is known that compounds A, B, and C are the following (not necessarily in order): C6H5COCH3 C6H5CHO C6H5CH2CHO (ii) Based on the above observations, state the identity of compound B. ….………………………………………………………………………………………[1] (iii) Give a simple chemical test to distinguish compounds A and C. In your answer, the observations for each compound must be stated. …………………………………………………………………………………………… ..………………………………………………………………………………………….. ……………………………………………………………………………………………. ….………………………………………………………………………………………[2]

3 9729/02/CJC JC2 Preliminary Examination 2022 [Turn over 2sp 2p 1 (a) Compounds A, B and C are all able to form hydroxynitriles when subject to the same reagents and conditions. (iv) State the reagents and conditions required for the above transformation. ….………………………………………………………………………………………[1] (v) The N atom of the nitrile group is sp hybridi sed. Complete the energy level diagram to show how the electrons are arranged in the second quantum shell of the N atom so that the bonding in the nitrile can occur. [1] (vi) Hence, suggest why nitriles are weaker bases than amines, given that N atom in amine is sp3 hybridised. …………………………………………………………………………………………… ..………………………………………………………………………………………….. …………………………………………………………………………………………… ….………………………………………………………………………………………[1] (b) Most of the world’s copper comes from the mining of copper -containing minerals. Copper ions exist as either one of the two oxidation states, +1 or +2. Two examples of such minerals are bornite and chalcopyrite. (i) Bornite has the chemical formula Cu5FeS4. Given that the oxidation state of S is ‒2 in bornite, write down the oxidation states of Cu and Fe in bornite. Oxidation state of Cu: ….…… Oxidation state of Fe: ………. [2] Energy

4 9729/2 CJC JC2 Preliminary Examination 2022 1 (b) (ii) Complete the diagram to show the arrangement of electrons in the third and fourth principal quantum shells of the ion of Fe in bornite. [1] Chalcopyrite is also composed of the elements Cu, Fe and S. Let the chemical formula of chalcopyrite be CuxFeSy. Both bornite and chalcopyrite react with HNO3 to give sulfur precipitate and NO2 gas. (iii) The balanced equation for the reaction of bornite and chalcopyrite with HNO3 are as follows. Cu5FeS4 + 26HNO3 → Fe(NO3)3 + 5Cu(NO3)2 + 4S + 13NO2 + 13H2O CuxFeSy + (6 + 4x)HNO3 → Fe(NO3)3 + xCu(NO3)2 + yS + (3 + 2x)NO2 + (3 + 2x)H2O When 1 mole each of bornite and chalcopyrite were fully reacted with HNO 3, bornite produced 64.2 g more sulfur precipitate and 1.92  105 cm3 more nitrogen dioxide than chalcopyrite, at room temperature and pressure. Determine the values of x and y. [3] [Total: 13] 3s 3p 3d 4s 4p

5 9729/02/CJC JC2 Preliminary Examination 2022 [Turn over 2 A sodium -vapor lamp is a gas -discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 5.89 x 10‒7 m. Low-pressure sodium lamps are highly efficient electrical light sources but due to their yellow light, they are widely used as street lamps. The yellow light is produced by an excited electron in a sodium atom falling from a 3p orbital to the 3s orbital. The wavelength for this transition is 5.898 x 10‒7 m. The energy, E (in joules), corresponding to the light of wavelength,  (in metre), is given by the following equation: λ hcE = where h is Planck’s constant = 6.63 x 10‒34 J s c is the speed of light = 3.00 x 108 m s‒1 (a) State the electronic configuration of a sodium atom in the ground state. Na: 1s2………………………………………………… [1] (b) Draw an energy level diagram to show the electron configuration of a sodium atom in an excited state that produces yellow light. [1] (c) Calculate the energy of the yellow light in (i) J (per atom) (ii) kJ mol‒1 [2]

6 9729/2 CJC JC2 Preliminary Examination 2022 2 (d) Sodium can react with water to form aqueous sodium hydroxide. Na(s) + H2O(l) → Na+(aq) + OH‒(aq) + ½ H2(g) The following data will be useful in this question. Enthalpy change of atomisation of Na(s) = +107 kJ mol‒1 Enthalpy change of neutralisation = ‒58 kJ mol‒1 Enthalpy change of hydration of Na+(g) = ‒405 kJ mol‒1 Enthalpy change of 2H+(aq) → H2(g) = ‒796 kJ mol‒1 Construct a fully labelled energy level diagram to determine the enthalpy change for the above reaction using relevant data from the above list, together with relevant data from the Data Booklet. [5] Na(s) + H2O(l) Energy/ kJ mol‒1 Na+(aq) + OH‒(aq) + ½ H2(g) ∆Hrxn

7 9729/02/CJC JC2 Preliminary Examination 2022 [Turn over 2 (e) The melting point of Na is 98 oC, whereas that of NaOH is 318 oC. Explain, in terms of structure and bonding, the differences in melting point between them. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ..………………………………………………………………………………………………… ………………………………………………………………………………………………….. ..………………………………………………………………………………………………… ………………………………………………………………………………………………….. ….…………………………………………………………………………………………….[2] [Total: 11]

8 9729/2 CJC JC2 Preliminary Examination 2022 3 (a) Liquid ammonia, like aqueous ammonia is a conductor of