NYJC H2 Chem Prelim P3 QP

1 NYJC 2017 H2 Chemistry 9729/03 PRELIM [Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9729/03 Paper 3 Free Response 19 SEP 2017 2 hours Candidates answer Section A on the Question Paper Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correcti on fluid. Section A Answer all questions . Section B Answer 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 to gether. The number of marks is given in brackets [ ] at the end of ea ch question or part question. 1 2 3 4 5 This document consists of 13 printed pages. KiasuExamPaper.com

2 NYJC 2017 H2 Chemistry 9729/03 PRELIM Section A Answer all the questions in this section. 1 (a) (i) Suggest why the melting point of MgO, A l 2 O 3 and SO 3 is decreasing in the following order MgO > A l 2 O 3 > SO 3 [2] (ii) Explain how the electronegativity of the elements in the oxides determine the type of bonding and hence the acid-base nature in MgO and P 4 O 10 .[ 2 ] (b) A student was given 3 unknown oxides A, B and C containing Na 2 O, Al 2 O 3 , and P 4 O 10 , The labels A to C do not correspond to the identities of the o xides. He was given 2 packets of sample mixture, each containing diffe rent mole ratios of oxides A to C given in the table. The student dissolved each sample mixture in half a beaker of w ater and recorded the observations of the resulting solution. Sample A B C Observation of resulting solution 1 1 1 7 Neutral solution 2 1 1 1 Highly acidic solution (i) Write a balanced equation when NaOH reacts with x A l 2 O 3 x P 4 O 10 [2] (ii) By considering the reactions of the oxides with water and the stoichiometric ratios obtained in (i) , account for the observations for s amples 1 and 2. Hence deduce the identities of A, B and C. [4] (c) The mineral dolomite is a double carbonate of magnesium and cal cium, with the formula of CaMg(CO 3 ) 2 . When a sample of impure dolomite was heated at 315 o C, x cm 3 of gas was collected which gave white ppt with lime water. When another sample of the same mass was heated at 530 o C, 2 x cm 3 of gas was collected. When 1.000g of dolomite was reacted with excess hydrochloric ac id, 0.450 g of gas was collected. (i) Write an equation to account for the reaction that took place at 315 o C. [1] (ii) Account for the different volume s of gases collected at 315 °C and 530 °C. [3] (iii) Determine the percentage purity of the impure dolomite sample. [2] KiasuExamPaper.com

3 NYJC 2017 H2 Chemistry 9729/03 PRELIM [Turn over (d) The following are some of the commonly used acids in food and b everage industries for various purposes like flavouring, preservatives and improving the texture of food. Their pK a values are given below. Name Structure pK a Carbonic acid H 2 CO 3 3.61 Ethanoic acid CH 3 CO 2 H 4.72 Cinnamic acid OH O 4.44 (i) By considering the structure of both acids, suggest and explain if ethanoic acid or cinnamic acid will react with NaOH(aq) first. [2] (ii) Explain, using appropriate equations, what would happen when ca rbon dioxide is bubbled into a solution containing the salt formed i n (i) . [2] [Total: 20] KiasuExamPaper.com

4 NYJC 2017 H2 Chemistry 9729/03 PRELIM 2 Phenylpropenes, for instance, 1 − phenylpropene, has been used as precursors for a variety of effective insecticides. CH CHCH 3 1-phenylpropene (a) Draw a labelled diagram to show the orbitals that form the C=C bond in 1 − phenylpropene, and state the type of hybridisation involved. [2] (b) 1 − phenylpropene reacts with iodine monochloride, I C l , in the presence of an inert organic solvent. (i) Describe the mechanism of this reaction, showing curly arrows, charges, dipoles and any relevant lone pairs. [2] (ii) Suggest the structure of another carbocation that can be formed f r o m t h e mechanism drawn in (i) . Hence, explain which is the preferred carbocation formed. [2] (iii) 1 − phenylpropene also reacts with aqueous iodine monochloride. When water is present, a different organic compound can be formed. Suggest the structure of this organic compound, and explain how it is formed with reference to the mechanism you have described in (i) . [2] (c) Hydroformylation is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of – CHO and a hydrogen atom to a carbon -carbon double bond. When an equimolar mixture of C 6 H 5 CH 2 CH=CH 2 , CO and H 2 at an initial total pressure of 120 atm is allowed to reach equilibrium at 500 K, the partia l pressure of C 6 H 5 CH 2 CH 2 CH 2 CHO is found to be 39.6 atm. Write the K p expression for this process and hence calculate a value for K p at 500 K, stating its units. [3] KiasuExamPaper.com

5 NYJC 2017 H2 Chemistry 9729/03 PRELIM [Turn over (d) Alcohol D, C x H y OH, is an alarm pheromones emitted by the Koschevnikov gland of honey bees. When 0.10 cm 3 of liquid D was dissolved in an inert solvent and an excess of sodium metal added, 10.9 cm 3 of gas was produced. When 0.10 cm 3 of liquid D was combusted in excess oxygen in an enclosed vessel, the volume of gas was reduced by 65 cm 3 . The addition of excess KOH(aq) caused a further reduction in gas volume of 131 cm 3 . All gases were measured at 273 K. (i) Use these data to calculate values for x and y in the molecular formula C x H y OH for D. [3] Alcohol D reacts with acidified K 2 Cr 2 O 7 , and can be dehydrated to alkene E. On treating E with an excess of hot acidified concentrated KMnO 4 , an equimolar mixture of ethanoic acid and butanone is produced. (ii) Use this information to deduce the skeletal formulae of D and E, explaining your reasoning. [2] (iii) State and explain with two reasons whether E can show cis-trans isomerism. [1] (e) Dinitrogen pentoxide, N 2 O 5 , has been used as a reagent to introduce the nitro group in arenes. It exists as a white solid of N 2 O 5 , with the structure O 2 N − O − NO 2 . N 2 O 5 can be produced by the following sequence. I : N 2 (g) + O 2 (g) Æ 2NO(g) ∆ H = +180 kJ mol − 1 II : NO(g) + ½ O 2 (g) Æ NO 2 (g) ∆ H = − 57 kJ mol − 1 III : 2NO 2 (g) + ½ O 2 (g) Æ N 2 O 5 (g) ∆ H = − 55 kJ mol − 1 (i) Draw the dot-and-cross diagram of N 2 O 5 . [1] (ii) Given that the bond energy of N − O bond is 210 kJ mol − 1 and usi