2020 MI Prelim Paper 3 mark scheme

Class Adm No Candidate Name: This question paper consists of 28 printed pages and 2 blank page. 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 responsibl e 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] Trimethylamine has a smaller electron cloud size than phenylamine, and thus has weaker instantaneous dipole -induced dipole forces of attraction between its molecules. Less energy is required to overcome them, and hence ; trimethylamine is likely to be more volatile / have a lower boiling point , exhibiting a stronger odour. ; (ii) When phenylamine and trimethylamine are burnt, only phenylamine burns with a smoky flame. Explain the above observation. [1] Phenylamine has a larger number of carbon atoms per molecule than trimethylamine, hence it undergoes incomplete combustion to produce soot / C(s). ; (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] C6H5NH2 + CH3COCl → CH3CONHC6H5 + HCl ; Amide ; (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] Ac