ACSI 2022 P2 Final (QP)

Anglo-Chinese School (Independent) Year 6 Preliminary Examination 2022 INTERNATIONAL BACCALAUREATE DIPLOMA PROGRAMME CHEMISTRY HIGHER LEVEL PAPER 2 Monday 12th September 2022 2 hours 15 minutes INSTRUCTIONS TO CANDIDATES • Write your candidate number in the box above. • Do not open this examination paper until instructed to do so. • Answer all questions. • A calculator is required for this paper. • A copy of the Chemistry Data Booklet is required for this paper. • Write your answers in the boxes provided. • The maximum marks for this examination paper is 90 marks. Candidate Number Candidate Full Name Class 6. This question paper consists of 23 printed pages, including the cover page. For examiner’s use Qn 1 /7 Qn 2 /13 Qn 3 /19 Qn 4 /12 Qn 5 /9 Qn 6 /12 Qn 7 /18 Wrong s.f. /units Total /90

2 Answer all questions. Write your answers in the boxes provided. 1. Copper is one of the most commonly used metal and exists in two oxidation states, +1 and +2. Mass spectroscopic analysis of a sample of copper gave the following results: % abundance 63Cu+ 69.17 65Cu+ 30.83 (a) Calculate the relative atomic mass of copper to two decimal places. [2] (b) State the number of protons, neutrons and electrons in the 65Cu2+ ion. [1] Number of protons: Number of neutrons: Number of electrons: (c) State the full electron configuration of the Cu+ ion. [1] (This question continues on the following page)

3 (d) Explain why, when ligands bond to the copper(II) ion causing the d–orbitals to split, the complex is coloured. [2] (e) If it takes 1.24  10−18 J of energy to eject an electron from the surface of copper metal, calculate the longest possible wavelength, in nm, of light that can ionize the metal. [1]

4 2. (a) Elements show trends in their physical properties across the Periodic Table. (i) Explain why the first ionization energy of oxygen is lower than the first ionization energy of nitrogen. [2] (ii) Explain why the atomic radius decreases across period 3, from sodium to chlorine. [2] (b) Dinitrogen monoxide, N 2O, causes depletion of ozone in the stratosphere. The Lewis (electron dot) structure of dinitrogen monoxide molecule can be represented as: Lewis structure I (i) Draw two other possible Lewis (electron dot) structures of dinitrogen monoxide with central atom N. [2] Lewis structure II Lewis structure III (This question continues on the following page) •• •• •• ••

5 (ii) Using formal charge, predict which Lewis structure I, II or III is preferred. Give a reason for your answer. [2] (iii) State and explain the shape of the dinitrogen monoxide molecule. [1] (This question continues on the following page)

6 (c) At the stratosphere, dinitrogen monoxide, N2O, is converted to nitrogen monoxide, NO, which is a free radical. NO catalyses the depletion of ozone. (i) Using a Lewis (electron dot) structure, explain why NO is highly reactive. [2] (ii) Write two equations to show how NO catalyses the depletion of ozone to form oxygen. [2]

7 3. Ascorbic acid, C6H8O6 is a potent antioxidant and a reducing agent that functions in fighting bacteria l infections and is commonly found in fruits such as oranges. Ascorbic acid is assumed to be a monobasic acid. The following equation illustrates the dissociation of ascorbic acid: ascorbic acid conjugate base of ascorbic acid C6H8O6 C6H7O6– The acid dissociation constant, Ka, for ascorbic acid is 6.82 x 10–5 mol dm–3. (a) A 25.0 cm3 of 0.500 mol dm–3 of the salt of the conjugate base of ascorbic acid, NaC6H7O6 was pipetted into a conical flask for titration with hydrochloric acid, HCl. (i) A pH meter was inserted into the conical flask containing NaC6H7O6. It gave a pH reading of more than 7. Explain, using a relevant equation, why a pH reading of more than 7 was obtained. [2] (This question continues on the following page)

8 (ii) Calculate the pH of the 25.0 cm3 of 0.500 mol dm–3 of NaC6H7O6 solution. [2] (iii) It was found that 1 3.30 cm 3 of HCl was required to reach the end –point of the titration . Calculate the concentration of HCl used. [1] (This question continues on the following page)

9 (b) A titration curve for the neutralization reaction between NaC6H7O6 and HCl is shown below: (i) Identify the chemical formula of the species present at the end–point of the titration. [1] (ii) State if the pH of the solution present at the end–point of the titration is • lesser than 7, • greater than 7, or • equal to 7 [1] (iii) With the aid of a suitable equation, explain how the solution present in region A can resist pH change upon addition of small amounts of acid. [2] (This question continues on the following page) A pH volume of HCl / cm3 13.30

10 (c) In another neutralization reaction, HCl of an identical concentration used in (a)(iii) was completely neutralized with 0.500 mol dm –3 of NaOH. The highest temperature reached was found to be higher compared to the neutralization of NaC6H7O6 with HCl. Explain the difference in the highest temperature reached. [2] (d) The standard enthalpy of formation of the NaCl formed from the neutralization between HCl and NaOH is −411 kJ mol−1. It was also found that the enthalpy change of atomization of sodium metal is +108 kJ mol−1. (i) With reference to the salt formed, define , with the aid of an equation, the term lattice enthalpy. [2] (This question continues on the following page)