SAJC_H2_CHEM_P3 Prelim

1 ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Chemistry Higher 2 9647/03 Paper 3 12 September 2011 2 hours Candidates answer on separate paper. Additional Materials: Writing paper, Data Booklet READ THESE INSTRUCTIONS FIRST: Write your name and civics group on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 8 printed pages including this page.

2 C O CH NH2 CH3 OH Answer any four questions 1 Deoxyribonucleic acid, DNA, is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, like a recipe or a code, sin ce it contains the instructions needed to construct other components of cells, such as proteins. Part of human DNA is formed using alanine, glutamine and lysine (which are listed in the following table). Amino Acid Structure Isoelectric point Alanine (Ala) 6.01 Glutamine (Gln) 5.65 Lysine (Lys) C O CH NH2 NH2 CH2 CH2 CH2 CH2 OH 9.74 (a) With reference to these three different types of amino acids only, (i) describe and exp lain with the aid of a diagram what is meant by the primary structure of proteins given that t he pH of the bloodstream is 7.3. (ii) describe how an excess amount of ethanol in th e bloodstream would affect the function of proteins. [5] (b) Ethanol, which is a commonly used organic solvent, has been used as the starting component in the synthesis of a variety of organic by -products. State the reagents and conditions needed to convert ethanol into: (i) 2-hydroxypropanoic acid (ii) methanoic acid [5] [Turn Over

3 1 (c) Drink driving is the act of driving a motor vehicle with blood levels of alcohol in excess of a specified limit. Hence, with drink driving becom ing an increasingly prevalent issue, the breathanalyser technology has become more precise and one of the cruder initial prototype was based on the oxidation process of ethanol using acidified potassium dichromate (VI). (i) Derive the ion electron half equation for the oxidation of ethanol to ethanoic acid. Hence, using relevant information from the Data Booklet, write a balanced equation for the oxidation of ethanol using acidified potassium dichromate (VI). (ii) When potassium dichromate (VI) is reacted with sodium hydroxide, a colour change from orange to yellow was observed . Suggest the identity of the yellow