2022 RVHS JC2 H2 CM Prelim P2 (QP)

River Valley High School 9729/02/PRELIM/22 [Turn over 2022 Preliminary Examination RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 2 1 J CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 14 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, class and name on all the work that 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. DO NOT WRITE IN ANY BARCODES. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. 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 Examiner’s Use Question Number 1 2 3 4 5 Marks 9 17 14 14 21 significant figures units Total 75 This document consists of 20 printed pages.

2 River Valley High School 9729/02/PRELIM/22 2022 Preliminary Examination 1 Ammonium salts are typically used in instant cold packs. The cold pack contains water and an inner pouch containing an ammonium salt. A crushing action causes the inner pouch to break and release the salt, which quickly dissolves to lower the pack’s temperature. To determine whether ammonium nitrate or ammonium chloride is more effective as the cold pack ingredient, a student decided to conduct an experiment to find out the enthalpy changes of solution of the two salts. He first added ammonium nitrate to water and determined the tempe rature change by plotting a suitable graph to correct for heat transfer. In a preliminary investigation, the enthalpy change of solution of ammonium nitrate was found to be approximately +26.0 kJ mol–1. (a) Define the term enthalpy change of solution. ……………………..…………………………………………………........…….. ……………………..…………………………………………………................. ……………………..…………………………………………………........…….. [1] (b) (i) The student was told to use 50.0 cm3 of water to conduct the experiment. Suggest a minimum mass of ammonium nitrate that could be used to effect a temperature change of 5.0 °C. Justify your choice with relevant calculations. You should assume that 4.18 J of heat energy changes the temperature of 1.0 cm3 of solution by 1.0 °C. [1]

3 River Valley High School 9729/02/PRELIM/22 [Turn over 2022 Preliminary Examination (ii) The student carried out the following procedure to find the enthalpy change of solution of ammonium nitrate. 1. Weigh accurately about 4.00 g of ammonium nitrate in a weighing bottle. 2. Using a 50 cm3 measuring cylinder, add 50.0 cm3 of deionised water into a polystyrene cup. 3. Stir the content s in the polystyrene cup gently with the thermometer and record the temperature every 0.5 minute. 4. At exactly 3.0 minutes, add the ammonium nitrate into the water. Do not read the temperature at this time. 5. Stir the mixture thoroughly and continue to record the temperature every 0.5 minute from 3.5 minutes to 9.0 minutes until constant temperature is reached. 6. Reweigh the weighing bottle with the residual ammonium nitrate. Sketch t he graph of temperature against time that you expect to obtain from the experiment. Indicate clearly on the graph how the temperature change, T, can be determined. [2]

4 River Valley High School 9729/02/PRELIM/22 2022 Preliminary Examination (c) Given the following data, d raw an energy level diagram to determine the standard enthalpy change of solution of ammonium chloride. Lattice energy of ammonium chloride = –705 kJ mol–1 Enthalpy change of hydration of NH4+ = –307 kJ mol–1 Enthalpy change of hydration of Cl– = –381 kJ mol–1 [3] (d) Explain how the magnitude of enthalpy change of hydration of chloride ions differs from that of bromide ions. ……………………..………………………………………………….................. ………………………..…………………………………………………….......... ……………………..………………………………………………….................. ………………………..…………………………………………………………… ……………………..………………………………………………….................. ………………………..…………………………………………………………… [2] [Total: 9]

5 River Valley High School 9729/02/PRELIM/22 [Turn over 2022 Preliminary Examination 2 Use of the Data Booklet is relevant to this question. Cobalt is a transition element that is used in the manufacture of magnetic alloys and catalysts. (a) Define the term transition element. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. [1] (b) The melting point of cobalt is 1495 °C while the melting point of calcium is 843 °C. Explain this in terms of structure and bonding of both elements. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. ……………………..…………………………………………………................. [2] (c) Aqueous cobalt( II) chloride, CoC l2, is a pink solution which gives the following reactions: (i) State the electronic configuration of the cobalt species in compound A. ……………………..…………………………………………………........ [1]

6 River Valley High School 9729/02/PRELIM/22 2022 Preliminary Examination (ii) Given the following information: [Co(NH3)6]3+ + e– = [Co(NH3)6]2+ E = +0.11 V By using relevant E values, account for the observation when solution B is left to stand in air. ……………………..…………………………………………………........ ……………………..…………………………………………………........ ……………………..…………………………………………………........ ……………………..…………………………………………………........ ……………………..…………………………………………………........ ……………………..…………………………………………………........ [2] (iii) Construct a labelled diagram to describe how the E value of the equation [Co(NH3)6]3+ + e– = [Co(NH3)6]2+ can be measured. [3] (iv) Indicate the direction of electron flow in your diagram above. [1]

7 River Valley High School 9729/02/PRELIM/22 [Turn over 2022 Preliminary Examination (d) D is a cobalt(III) complex with the formula Co(NH3)aCl3. In a ligand exchange reaction , 3.501 g of D is dissolved in 500 cm 3 of water. 25.0 cm3 of this solution requires 18.75 cm 3 of 0.0400 mol dm–3 of EDTA(aq) for complete reaction. In another experiment, when excess AgNO3(aq) is added to 23.340 g of D, 14.340 g of solid AgCl is formed. (i) Given that 1 mol e of D reacts with 1 mol e of EDTA, show that the molar mass of D is 233.4 g mol–1. [2] (ii) Show that 1 mol e of D will form 1 mole of AgCl when reacted with excess AgNO3. [1] (iii) Deduce the value of a. Hence, state the formula of the cation in D. [2]

8 River Valley High School 9729/02/PRELIM/22 2022 Preliminary Examination (iv) When D undergoes reduction, followed by exposure to excess carbon monoxide gas, an octahedral complex E, Co(CO)4Cl2, is formed. Given that E has no net dipole moment, Draw the s hape of E, showing the arrangement of the ligands. [2] [Total: 17] 3 (a) Hydration of alkenes can be car