2020 MI Prelim Paper 3

Class Adm No Candidate Name: This question paper consists of 28 printed pages and 2 blank pages. 2020 End-of-Year Examinations Pre-University 3 H2 CHEMISTRY 9729/03 Paper 3 Free Response 18th Sep 2020 2 hours Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. Section A: Answer all questions Section B: Answer any 1 question A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Section A Section B Total Question 1 2 3 4 5 Marks 25 20 15 20 20 80

2 Section A Answer all questions from this section. 1 Phenylamine, C6H5NH2, otherwise known as aniline, is commonly used in the manufacture of industrial chemicals. The family of amines tend to exhibit strong odours. The more volatile the amine, the stronger the odour. Trimethylamine, (CH 3)3N, is the compound responsible for the fishy odour associated with rotting fish. (a) (i) Suggest, with explanation, whether phenylamine or trimethylamine is likely to exhibit a stronger fishy odour. [2] (ii) When phenylamine and trimethylamine are burnt, only phenylamine burns with a smoky flame. Explain the above observation. [1] [1] (iii) The reaction between phenylamine and ethanoyl chloride, CH3COCl, takes place rapidly at room temperature, releasing a gas in the process. Write a balanced chemical equation for the reaction between phenylamine and ethanoyl chloride, and identify the functional group formed in the product. [2] (iv) A laboratory assistant wants to synthesise the product in (iii). However, ethanoyl chloride is unavailable, so he opts to use ethanoic acid in place of ethanoyl chloride. Explain why the desired product is not obtained. [1] (v) State the reagents and conditions needed to produce ethanoyl chloride from ethanoic acid. [1] ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………...

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4 ………………………………………………………………………………………………………………... (b) Phenylamine can be synthesised from nitrobenzene via many different reactions. One such reaction involves using palladium on carbon (Pd/C) catalyst, at 200–300 °C: (i) Identify the type of reaction carried out above. [1] (ii) Palladium on carbon (Pd/C) is a fine powder made by depositing palladium metal in the porous cavities of activated charcoal. State the type of catalysis involved, and suggest why palladium metal needs to be in the form of a fine powder. [2] (iii) A chemist carries out this reaction and obtains a percentage yield of 96%. Suggest why it is difficult to achieve 100% yield. [1] ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... ………………………………………………………………………………………………………………... …………………………………………………………………… …………………………………………... ………………………………………………………………………………………………………………...

5 [Turn over ………………………………………………………………………………………………………………... (c) The –CH=CH2 group of phenylethene directs incoming substituents to the 3 -position of the benzene ring, while the –NH2 group of phenylamine directs incoming substituents to the 2-position of the benzene ring. This is known as the orientation effect. A student claims that this orientation effect is due to “–CH=CH2 and –NH2 having orbital overlaps with the benzene ring”. Under the right set of reagents and conditions used, the following products are obtained from phenylethene and phenylamine respectively: (i) State the corresponding reagents and conditions for steps I and II. [2] (ii) Describe the mechanism of Reaction 1. In your answer, show all relevant lone pairs and curly arrows involved in the mechanism. [4] (iii) State the hybridisation for each of the two carbon atoms in the –CH=CH2 substituent of phenylethene. [1] (iv) With the aid of an appropriate orbital diagram, illustrate in phenylethene, the orbital overlaps of –CH=CH2 with the benzene ring. You need only show the relevant orbitals of the carbon atoms involved. [2] (v) Briefly explain why it would be incorrect to say that “–CH=CH2 is an electron-withdrawing group”. [1] (vi) Suggest a chemical test to distinguish between phenylethene and phenylamine. [2]

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