Mock Paper 2

CHEMISTRY 9729/02 Paper 2 Structured Questions 2 hours READ THESE INSTRUCTIONS FIRST 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 provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question, or part question. Question 1 2 3 4 5 6 Total Marks scored Maximum Marks 12 11 11 12 8 21 75 This document consists a total of 18 printed pages, including this cover page.

Paper by @ijustloveh2chem 2 1 (a) In 1967, scientists around the world met up to determine the standard of the second. Prior to that, the second was not properly standardised across the world. 133Cs atomic clocks were used to determine the standard of the second. When an atom is placed under an electromagnetic field, its valence electrons oscillate at a fixed rate. The rate of oscillation was used to determine the standard of the second. It’s estimated that the margin of error is at 1 second per 1.4 million Earth years. (i) Cs is vaporised to ensure more accurate measurements. The interactions in Cs at room temperature may interfere with the measurements taken. Describe these ‘interactions’ in Cs at room temperature. Refer to the structure and bonding in Cs. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (ii) As there were many atomic clocks at that time, much of the discussion centred around what element was to be used. 2 of the criteria are listed below: • low number of active electrons • easy to vapourise A student proposed 2 other elements that can be used: Pb and Li. Suggest why these elements are poorer candidates compared to Cs. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (b) (i) State how the reducing power of the Group 1 metals varies down the group with reference to relevant standard electrode potential values. ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [1]

Paper by @ijustloveh2chem 3 (ii) Explain the variation of the first ionisation energy of the Group 1 metals down the group. ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [1] (c) (i) A student attempted to measure the standard electrode potential of the reduction of the aqueous Cs+ ion to Cs metal directly against a standard hydrogen electrode. Explain why his method would not work. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (ii) Molten CsF was electrolysed. A constant current of 2.00 A was passed through the setup for 48 hours. Calculate the mass of molten Cs that is extracted. [2] (d) Group 1 metals form peroxides (general formula: M2O2) after long exposure to oxygen. Under heating, these peroxides decompose to their respective oxides, and oxygen gas is produced as a byproduct. Suggest an explanation for the variation of the decomposition temperatures of the peroxides Na2O2, K2O2, Rb2O2 and Cs2O2. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ………………………………………………………………………………………………………… [2] [Total: 12]

Paper by @ijustloveh2chem 4 2 But-3-en-2-one may be reduced by NaBH4 to form a racemic mixture of butan-2-ol. (a) (i) This reaction occurs through an intermediate. The intermediate is either A or B. By considering which intermediate can react with NaBH4, suggest which intermediate is produced in this reaction. Explain your answer. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (ii) State 2 tests which may distinguish A from B. State the accompanying observations. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (iii) Explain why a racemic mixture of butan-2-ol is produced. ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [1] O OHNaBH4 O OH A B

Paper by @ijustloveh2chem 5 (iv) State another set of reagent(s) and conditions which converts but-3-en-2-one to butan-2-ol. …………………………………………………………………………………………………… [1] (b) Equal amounts of aqueous Br2 were added to 2 separate test tubes X and Y containing equal amounts but-3-en-2-one and B respectively. In test tube Y, 2 products were formed. One product contains a 3-membered ring. (i) Describe the mechanism in test tube Y where the product containing the 3-membered ring is formed. [3] (ii) Explain whether the solution in test tube X or Y will decolourise faster after aqueous bromine is added to it. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] [Total: 11]

Paper by @ijustloveh2chem 6 3 (a) State the electronic configuration of the Ni2+ ion. ………………………………………………………………………………………………………… [1] (b) An aqueous solution of NiCl2 is green. This is due to the colour of the ion [Ni(H2O)6]2+. Explain why the [Ni(H2O)6]2+ ion is green in colour. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ………………………………………………………………………………………………………… [3] (c) State Le Chatelier’s principle. …………………………………………………………………………………………………………… ………………………………………………………………………………………………………… [1] (d) Equilibrium 1 and 2 are 2 reactions that the [Ni(H2O)6]2+ ion may undergo. equilibrium 1 [Ni(H2O)6]2+ + 2 OH- ⇌ Ni(OH)2 + 6 H2O equilibrium 2 [Ni(H2O)6]2+ + 6 NH3 ⇌ [Ni(NH3)6]2+ + 6 H2O A student recorded the following observation: When aqueous ammonia was added dropwise, a green precipitate formed. The green precipitate subsequently dissolved to form a blue solution after addition of more aqueous ammonia. Use Le Chatelier’s principle to explain the observation. …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ………………………………………………………………………………………………………… [2]

Paper by @ijustloveh2chem 7 (e) When 4 ligands are bonded to a metal centre, the geometry of the metal centre may be either square planar or tetrahedral. The complex ion [Ni(Br)2(CN)2]2- exhibits stereoisomerism. Draw the 3-dimensional structures of the 2 stereoisomers of [Ni(Br)2(CN)2]2- and assign a stereochemical descriptor for the isomers. [2] (f) The Mond process is used to purify nickel from nickel ores that contain trace amounts of iron and cobalt. The process may be described as: 1. Impure nickel reacts with gaseous carbon monoxide (CO) to form Ni(CO)4. 2. The liquid Ni(CO)4 collected is then heated to reform pure nickel metal. (i) Draw the dot-and-cross diagram of CO. [1] (ii) Briefly explain why this process has fallen out of use. ……………………………………………………………………………………………………… …………………………………………………………………………………………………… [1] [Total: 11]

Paper by @ijustloveh2chem 8 4 (a) Phenolphthalein (Mr = 318.3) is a common indicator used in acid-base titrations. (i) Phenolphthalein can be synthesised from phenol. State the type of reaction occurring above. …………………………………………………………………………………………………… [1] (ii) Complete the skeletal structure of the resultant organic product(s) formed when phenolphthalein is subjected to the follow