2022 DHS Y6 H2 Prelim Paper 2 QP

© DHS 2022 9729/02 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 13 September 2022 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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. You may lose marks if you do not show your working or if you do not use appropriate units. 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 1 12 2 12 3 14 4 16 5 21 Total 75 This document consists of 21 printed pages and 3 blank pages.

2 © DHS 2022 9729/02 Answer all the questions in the spaces provided. 1 (a) Describe the thermal decomposition of the hydrogen halides HC l, HBr and H I and explain any variation in their thermal stabilities. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………... [3] (b) Tert-butyl alcohol reacts with hydrogen chloride according to the equation shown. (CH3)3COH + HCl → (CH3)3CCl + H2O This reaction occurs in three steps. step 1 protonation of –OH group in (CH3)3COH to produce (CH3)3COH2+ cation step 2 loss of H2O molecule from (CH3)3COH2+ to produce a carbocation step 3 chloride ion reacts with carbocation to produce (CH3)3CCl (i) Describe the mechanisms which occur in steps 2 and 3. Use curly arrows to show the movement of electrons and label the slow step. [3]

3 © DHS 2022 9729/02 [Turn over (ii) An enantiomerically pure alcohol, where the carbon atom bonded to the –OH group is chiral, was used for the reaction in (b). Use your answer in (b)(i) to deduce the stereochemical outcome of this reaction. Explain your reasoning. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………................. [2] Tert-butyl alcohol also reacts with solid phosphorus pentachloride, PC l5, to produce (CH3)3CCl. (iii) With the aid of a suitable equation, explain why the reaction is not carried out in aqueous medium. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………................. [2]

4 © DHS 2022 9729/02 (c) (CH3)3CCl is one of the two monochlorinated products of the reaction between an alkane, X, and chlorine gas in the presence of UV light. (i) Draw the structure of the alkane, X, and state the IUPAC name of the other monochlorinated product. IUPAC name ………………………….……..……………….……………………… [1] (ii) The rate of formation of (CH3)3CCl is faster than that of the other monochlorinated product. Suggest an explanation for the different rates of reaction. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………….................. [1] [Total: 12]

5 © DHS 2022 9729/02 [Turn over 2 (a) The following equilibrium occurs when ethanal is mixed with water. G = −0.282 kJ mol–1 Use relevant data from the Data Booklet to calculate the equilibrium constant, K, for the reaction. [2] (b) The aldol reaction is a useful reaction that forms a carbon–carbon bond between two carbonyl compounds. For example, t wo ethanal molecules can be combined using the aldol reaction. The carbonyl carbon, a, of one ethanal molecule forms a covalent bond with a carbon atom, b, of another ethanal molecule. Carbon atom, b, must be adjacent to carbonyl carbon, c. (i) When different carbonyl compounds are used in an aldol reaction, a mixture of structural isomers is formed. Suggest two possible structural isomers that can be formed if propanone, CH3COCH3, and propanal, CH3CH2CHO, are mixed. structural isomers [2]

6 © DHS 2022 9729/02 (ii) Both propanal and propanoic acid can be formed from propan –1–ol in the same reaction. Describe the reagents and conditions needed to ensure that the reaction yields propanal as the major product. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………….................. [2] (c) Some tin reagents are useful in organic chemistry. Tin forms two chlorides, SnCl2 and SnCl4. (i) A mixture of these chlorides was found to contain 50.0% by mass of tin. Calculate the percentage by mass of SnCl2 in the mixture. [3]

7 © DHS 2022 9729/02 [Turn over (ii) Tin exists in +2 or +4 oxidation states in many of its compounds. Great care must be taken to ensure the correct oxidation state of tin is formed. A student proposed the following preparation methods to prepare the two chlorides, SnCl2 and SnCl4. Preparation method for SnCl2 Heating tin with hydrochloric acid produces hydrogen gas. Careful evaporation of the water and dehydration produces white solid SnCl2. Preparation method for SnCl4 Passing chlorine gas over heated tin produces colourless liquid SnCl4 as the only product. Explain if the preparation methods proposed above are feasible without reference to any calculation. Use relevant standard electrode potentials from the Data Booklet. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………….................. [3] [Total: 12]

8 © DHS 2022 9729/02 3 (a) Compound N, C3H4O3, liberates a gas when treated with aqueous sodium carbonate. (i) Identify the gas and state the functional group that is present in compound N. …………………………………………………………………………………………. ………………………………………………………………………….................. [1] When 0.10 cm3 of liquid compound N was dissolved in an inert solvent and an excess of sodium metal added, 15 cm3 of gas was produced at 303 K and 1 atm. [Density of compound N = 1.093 g cm−3] (ii) Calculate the ratio of the amount of compound N reacted to the amount of gas that is produced. [1] (iii) Use your answers in (a)(i) and (a)(ii) to suggest two possible structures of compound N. Explain your reasoning. possible structures of compound N …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………….................. [3]

9 © DHS 2022 9729/02 [Turn over Compound N, C3H4O3, is formed as the only organic product when a neutral organic compound M, C 4H8O3, is heated with acidified KMnO 4. M does not decolourise aq