DHS Prelim P3_QP

DUNMAN HIGH SCHOOL Preliminary Examination 2014 H2 CHEMISTRY (9647/03) 1 (a) Lawsone is the dye that is extracted from the henna plant, Lawsonia inermis . Although its natural colour is yellow, lawsone reacts with the proteins in hair and skin to produce the characteristic brown henna colour. Compound A is a derivative of lawsone. O O OH lawsone O O OH A (i) Name two functional groups in A, other than the phenyl group. (ii) Describe a reaction, with reagent and condition(s), to confirm one of the functional groups in A. Describe the observations you would make. (iii) Only one organic compound can be formed when lawsone is reacted with aqueous Br 2, through the loss of one water molecule. Suggest the structural formula of this compound. [4] (b) Compound B can be oxidised to lawsone by acidified K 2Cr2O7 involving two moles of electrons lost per mole of B. O O OH OH OH OH lawsoneB (i) With the use of the Data Booklet , construct a balanced half–equation for the oxidation of B and a balanced equation for the overall reaction. You are to use the molecular formulae of lawsone (C 10H6O3), B (C 10H8O3) and Cr 2O7 2– in your equations. (ii) Calculate the concentration of a solution of compound B given that 20.0 cm 3 of this solution required 12.50 cm3 of 0.050 mol dm–3 K2Cr2O7 solution to reach end–point. [4] (c) When lawsone is reacted under suitable condition, compound C is produced. Reacting C with ethanoyl chloride produces a neutral compound D, with molecular formula C 12H8O4. C12H8O4 O O O - C CH3 Cl O D (i) The production of D occurs via a two–step mechanism.

DHS Prelim Exam 2014 H2 Chemistry Paper 3 – Mark Scheme © DHS 2014 9647/03 2 Step I: B and ethanoyl chloride reacts to form an intermediate E as shown. O O O CH3 O Cl EStep II: A chloride ion is eliminated to form D. Outline the two mechanism steps by drawing relevant curly arrows, partial charges and lone pair of electrons in your answer. Label the steps clearly. (ii) Hence or otherwise, draw the structural formula of D. [3] (d) Another compound F, in addition to D, is also produced in the above reaction involving C and ethanoyl chloride. O O O CH3 O F (i) Draw the structure of the nucleophile, G, involved in the formation of F. (ii) Hence, suggest with the use of curly arrows, to show how G is formed from C. [2] (e) When added to silver nitrate solution, ethanoyl chloride forms a white precipitate, while ethanoyl bromide forms a cream precipitate. (i) Identify the precipitates. (ii) Write an equation for the formation of white precipitate from ethanoyl chloride. (iii) State and explain which of the two precipitate will be soluble in aqueous ammonia. [7] [Total: 20] 2 (a) Over 80% of all lead produced ends up in lead–acid batteries, with lead metal and lead(IV) oxide used in them. In addition to starter batteries for road vehicles, lead and lead( IV) oxide a