2017 RVHS H2 Chemistry P2 Soln

River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II RIVER VALLEY HIGH SCHOOL YEAR 6 PRELIMINARY EXAMINATION II CANDIDATE NAME CLASS CENTRE NUMBER S 3 0 4 4 INDEX NUMBER 0 0 H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 13 Sep 2017 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST. DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Write your name, class and index number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. 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. For Examiner’s Use Paper 2 P2 1 2 3 4 5 SF UNITS Total (P2) 17 14 14 15 15 75 P1 30 P3 80 Total 185 P4 55 Grade This paper consists of XX printed pages.

2 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II Answer all questions in the spaces provided. 1 Among the many pharmaceutical drugs manufactured worldwide, one of the most important types is the painkillers. The structures of three such painkillers are shown. ibuprofen (Mr = 206) paracetamol (Mr = 151) aspirin (Mr = 180) Ibuprofen is used to treat arthritis and relieve pain, fever and swelling. It is available over -the-counter in 200 and 400 mg tablets. The recommended dosage varies with body mass and indication , but 1.20 g is considered the maximum daily adult dosage. Long term use of ibuprofen can lead to stomach ulcers. Ibuprofen can be synthesised via the following process: (a) A man bought some ibuprofen tablets of dosage 200 mg over the counter and consumed one pill 4 times a day. Explain if this level of consumption safe for the man. Since 4 x 200 = 800 mg is lower than the maximum dosage of 1200 mg, the level of consumption is safe for the man. [1] (b) State the type of reaction that converts Compound A to B. Electrophilic substitution [1]

3 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II (c) In the laboratory, C ompound C can be converted to ibuprofen using a 3-step synthesis route. Suggest reagents and conditions for each step, and draw the structures of all intermediates. [5] (d) Young children often find it difficult to swallow tablets. Thus, ibuprofen is supplied as an “infant formula” emulsion. Given that i buprofen and water are immiscible , an emulsifier such as polysorbate 80 is used to create a homogeneous mixture. polysorbate 80 Explain why this molecule is able to act as an emulsifier. The -OH polar groups allow the molecule to be soluble in water, while the non-polar hydrocarbon groups allow the molecule to be soluble in oil / non- polar liquids. [1] (e) A certain pharmaceutical brand claims that the ibuprofen tablets it manufactures are 95.0% pure by mass.

4 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II To investigate this claim, 5.00 g of a sample was crushed and di ssolved in 250 cm3 of 0.450 mol dm−3 aqueous KOH. 25.0 cm3 of this solution was withdrawn and titrated against sulfuric acid. The unreacted KOH in this solution required 25.50 cm3 of 0.180 mol dm–3 of sulfuric acid for complete neutralisation. Showing relevant calculations, deduce if the claim is valid. Amount of H2SO4 = 25.50 1000 × 0.180 = 0.00459 mol Amount of unreacted KOH = 0.00459 x 2 = 0.00918 mol Amount of unreacted KOH (in 250 cm3) = 0.0918 mol Amount of KOH reacted with ibuprofen sample = 250 1000 × 0.450 − 0.0918 = 0.0207 mol Since ibuprofen  KOH, Amount of ibuprofen = 0.0207 mol Mass of ibuprofen = 0.0207 x [13(12.0) + 18(1.0) + 2(16.0)] = 4.26 g Percentage purity = 4.26 5.00 × 100% = 85.2% Hence, the claim is invalid. [3] (f) Compare the acidity of ibuprofen and aspirin. Explain your answer. Aspirin is a stronger acid than ibuprofen. The anion of aspirin, , is more stable than the anion of ibuprofen, , as the negative charge is delocalised over the COO− group and into the benzene ring. [2] (g) Describe two simple chemical tests to distinguish between ibuprofen, paracetamol and aspirin. Test: Add neutral FeCl3(aq) [4]

5 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II Observations: Violet colouration form s for paracetamol. No violet colouration forms for ibuprofen and aspirin. Test: Heat with acidified KMnO4(aq) Observations: Purple KMnO 4 turns colourless for ibuprofen. KMnO 4 remains purple for paracetamol and aspirin. [Total: 17] 2 (a) Gaseous ethane can be used as a fuel for campers. A company manufactures compressed gaseous ethane in 400 cm3 metal canisters. A typical metal canister at room temperature contains compressed gaseous ethane at a pressure of 4.00 atm. (i) Suggest a reason why gaseous ethane in the metal canister does not behave like an ideal gas. Due to high pressure in the canister , volume of the ethane molecules is not negligible compared to volume of the metal canister / intermolecular forces of attraction between ethane molecules are not negligible. [1] (ii) One metal canister is used for heating water and the pressure decreases from 4.00 atm to 1.50 atm. Assuming that the compressed ethane behaves ideally, calculate the mass of water at room temperature that could be brought to boiling if the process is 80% e fficient. The enthalpy change of combustion of ethane is 1420 kJ mol-1. Using pV = nRT, (2.50 x 101325)(400 x 10-6) = n (8.31)(293) n = amount of ethane used = 0.0416 mol Heat evolved from combustion of ethane = 0.0416 x 1420 = 59.1 kJ 0.80 x 59.1 x 103 = Mass of water x 4.18 x (100 – 20) Mass of water = 141 g [3] (iii) Suggest a reason why butane is a better fuel for campers compared to ethane.

6 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II Butane has a higher magnitude of enthalpy change of combustion / More heat is produced per mole of butane combusted / Butane is more compressible, and therefore more portable. [1] (b) Calcium fluoride is used for dental protection. It dissolves readily in water with an enthalpy change of solution of 125 kJ mol -1. It is given that the lattice energy of calcium fluoride is 2350 kJ mol -1 while the enthalpy change of hydration of calcium ion is 1560 kJ mol-1. With the aid of a labelled energy level diagram, calculate the enthalpy change of hydration of fluoride ion. By Hess’ Law, Hsoln(CaF2) = LE(CaF2) + Hhyd(Ca2+) + 2Hhyd(F) 125 = (2350) + (1560) + 2Hhyd(F) Hhyd(F) = 458 kJ mol-1 [4] (c) Liquid hydrazine reacts with oxygen to form nitrogen and steam which could involve the following energy cycle shown below. Ca2+(g) + 2F(g) CaF2(s) Ca2+ (aq) + 2F(aq) LE(CaF2) Hhyd(Ca2+) + 2Hhyd(F) Hsoln(CaF2) Energy

7 River Valley High School 9729/02 [Turn over 2017 Preliminary Examinations II (i) Given that the enthalpy change of vapourisation of hydrazine is +58.0 kJ mol -1, use appropriate bond energies from the Data Booklet to calculate the enthalpy change of reaction between liquid hydrazine