NJC Prelim P3_QP

1 NJC SH2 Prelim Exam 9729 / 03 / 18 [Turn Over NATIONAL JUNIOR COLLEGE SH2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Data Booklet Answer Paper 9729/03 Monday 10 Sep 2018 2 hours READ THESE INSTRUCTIONS FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid/tape. Section A Answers all questions. Section B Answers one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. This document consists of 11 printed pages.

2 NJC SH2 Prelim Exam 9729 / 03 / 18 [Turn Over Section A A n s w e r all the questions in this section. 1 (a) The melting points of some compounds are given Substance Octan-1-ol Iodine Fullerene Graphite Formula CH 3(CH2)7OH I2 C60 C Melting point/ K 277 286 873 >3000 (i) Explain why the melting points of octan-1-ol and iodine are comparable. [2] (ii) Explain why the melting point of graphite is higher than that of fullerene. [2] (b) In 1932, Harry Lister Riley and coworkers published their findings on the use of selenium dioxide, SeO 2, in the synthesis of aldehyde and ketone functional groups. One of such reactions is shown below. CH 3COCH3 + SeO2 CH3COCHO + Se + H2O reaction I Using the synthetic method above in one of your steps, devise a three–stage synthesis of compound B from compound A. O OH O OH Compound A Compound B [5] (c) The most common source of acidity in water is dissolved carbon dioxide. Carbon dioxide enters the water through equilibrium with the atmosphere. CO2(g) CO2(aq) KH = 3.3 x 10–4 mol dm–3 kPa–1 where K H is known as the Henry’s Law constant given by the equation: [CO2(aq)] = KH × ஼ைଶ Carbon dioxide can react with water to form carbonic acid as shown in the following reaction. CO 2(aq) + H2O H2CO3(aq) Kc = 1.3 × 10–3 (i) Calculate [CO2(aq)] at a pressure of 101.3 kPa, given that air contains 0.035% by volume of carbon dioxide. [2] (ii) Using your answer from (i), calculate [H2CO3].