RVHS_H2_CHEM_P3_QP_RV Prelim

River Valley High School 9647/03/PRELIM/14 2014 Preliminary Examination II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION (II) CANDIDATE NAME CLASS 6 CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9647/03 Paper 3 Free Response 23 September 2014 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Graph Paper Cover Page Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class, centre number and index number on all the work you hand in. Write in dark blue or black pen on both sides of paper. 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. Begin each question on a fresh sheet of paper. A Data Booklet is provided. Do not write anything on it. 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. At the end of the examination, fasten all your work securely together, with the cover page on top. This document consists of 16 printed pages.

2 River Valley High School 9647/03/PRELIM/14 2014 Preliminary Examination II Answer any four questions. 1 (a) TRIS is an organic compound with the formula (HOCH 2)3CNH2. It is extensively used in biochemistry and molecular biology as a component of buffer solutions. TRIS The table below summarises key inform ation about TRIS and other amines. Compound m.p./C b.p./C pKb Odour CH3NH2 93 6 3.43 Fishy CH3CH2NH2 80 20 3.19 Fishy C6H5NH2 6 184 9.37 Fishy TRIS 176 219 5.93 Characteristic (i) What is meant by the term buffer? (ii) 25.0 cm 3 of 0.10 mol dm –3 TRIS is titrated against 0.20 mol dm –3 hydrochloric acid. Calculate the pH of the solution when the following volumes of hydrochloric acid are added. 1. 0 cm3 2. To reach equivalence point 3. 30 cm3 (iii) Apart from its relatively low cost, suggest why TRIS is suitable for use in biochemistry and molecular biology experiments. [6]

3 River Valley High School 9647/03/PRELIM/14 2014 Preliminary Examination II (b) C6H5NH2, also known as aniline, played a key role in the proliferation of synthetic dyes. Many of these compounds involve azo dyes, which contain two aromatic fragments connected by a N=N double bond. Azo dyes are prepared in a two -step reaction, the first being the synthesis of an aromatic diazonium ion from an aniline derivative (note: alkyl diazonium ions are very unstable). The next step is the coupling of the diazonium salt with an aromatic compound. The reaction scheme is shown below. (i) A student who was interested in studying the rate of reaction of the diazotisation step found the following mechanism on the internet. HONO ⇌ H+ + ONO

4 River Valley High School 9647/03/PRELIM/14 2