DHS H1 CHEM P2 QP

This question paper consists of 15 printed pages and 1 blank page. © DHS 2015 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2015 Year 6 H1 CHEMISTRY 8872/02 Paper 2 Section A (Structured Questions) 16 September 2015 Paper 2 Section B (Free–Response Questions) 2 hours Additional Materials: Data Booklet, Writing Paper INSTRUCTIONS TO CANDIDATES 1 Answer all questions in Section A, and any two questions in Section B. 2 Write your name and class on this cover page. Section A 3 Write your answers in the spaces provided on this question paper. 4 You are advised to spend a maximum of 1 hour on Section A. Section B 5 Write your name and class on the Cover Sheet provided. 6 Write your answers on the separate writing papers provided. 7 Answer any two questions. 8 Start each question on a fresh sheet of paper . Marks will be deducted if you fail to do so. 9 At the end of the examination, fasten all your work securely together with the Cover Sheet on top. 10 You are advised to spend a maximum of 1 hour on Section B. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all workings in calculations. You are reminded of the need for good English and clear presentation in your answers. For Examiner’s Use Question No. Section A Marks 1 9 2 8 3 8 4 7 5 8 Total 40

2 © DHS 2015 8872/02 [Turn over Section A Answer all questions in the spaces provided. 1 (a) Calcium ethanedioate, CaC 2O4, is a white needle–like crystalline solid. When a pure sample of anhydrous CaC 2O4 was heated strongly at 400 C until no further change in mass is observed, a white solid B and 0.028 g of carbon monoxide gas were obtained as the only products. (i) Given that 1 mole of CaC 2O4 decomposes to give 1 mole of CO(g), write a balanced equation for the thermal decomposition of CaC2O4 and identify solid B. equation : solid B : (ii) Hence, determine the mass of B obtained in the reaction. [3] (b) The formula of potassium hydrogen ethanedioate can be written as K xHy(C2O4)z. In an experiment to determine the values of x, y and z, 4.50 g of this compound was dissolved in water and the solution made up to 1 dm3. 20.0 cm 3 of the solution was pipetted into a conical flask and then titrated with 0.0200 mol dm ––3 KMnO4 in an acidic medium. It was found that 16.50 cm 3 of KMnO 4(aq) was needed for the complete reaction with ethanedioate ions, C 2O4 2–, present. During the titration, effervescence of carbon dioxide is produced. Given the reaction of manganate(VII) in acidic medium as: MnO 4 – + 8H+ + 5e– Mn2+ +4H2O (i) Write a balanced half–equation for the reaction of C2O4 2 during titration. half– equation :

3 © DHS 2015 8872/02 [Turn over (ii) Calculate the mass of C2O4 2– present in 1 dm3 of the solution. (iii) Given that 4.50 g of potassium hydrogen ethanedioate contains 0.060 g of hydrogen, calculate the mass of potassium present in the sample. (iv) Hence, determine the values x, y and z. [6] [Total: 9]

4 © DHS 2015 8872/02 [Turn over 2 The following table lists the standard enthalpy changes of combustion, Hc , of some monohydric alcohols. alcohol Hc  / kJ mol–1 methanol –715 ethanol –1367 propan–1–ol ? butan–1–ol –2671 . (a) Write an equation to represent the standard enthalpy change of combustion of propan–1–ol. [1] (b) (i) The difference in the standard enthalpy change of combustion of methanol and ethanol is –652 kJ mol –1. By considering the structures of the two alcohols, suggest the significance of this difference. (ii) Hence suggest a value of Hc  for propan–1–ol. Suggest a value of Hc  for propan–1–ol : (iii) Given that Hf [H2O(l)] = –286 kJ mol 1 and Hf [CO2(g)] = –394 kJ mol 1, and using your answer to (b)(ii), calculate the standard enthalpy change of formation of propan–1–ol, Hf [CH3CH2CH2OH(l)]. [4]

5 © DHS 2015 8872/02 [Turn over (c) Ethanol is metabolised in the body by an enzyme called alcohol dehydrogenase. Define enzyme and describe how alcohol dehydrogenase affects the rate of ethanol metabolism in the body. [3] [Total: 8]

6 © DHS 2015 8872/02 [Turn over 3 (a) Below is the incomplete sketch of the plot of first ionisation energies against atomic (proton) numbers for ten elements. (i) On the diagram above, use crosses ( ) to mark the first ionisation energies of Si and S. (ii) Explain why the first ionisation energy of potassium is lower than that of sodium. (iii) State which of the ten elements is likely to have the lowest second ionisation energy and write an equation to represent the second ionisation energy of this element. element : equation : [4] 0 200 400 600 800 1000 1200 1400 1600 10 11 12 13 14 15 16 17 18 19 20 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar  19K  20Ca first ionisation energy / kJ mol–1 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar 19K 20Ca atomic number

7 © DHS 2015 8872/02 [Turn over (b) X, Y and Z are elements in Period 3 of the Periodic Table. The oxide of X dissolves sparingly in water to give a weakly alkaline solution. The oxide of Y does not react with water, but reacts with both acids and bases. Z reacts with oxygen to form a covalent oxide with a very high melting point. (i) Fill in the table below by identifying the elements X, Y and Z and suggest the pH of their chlorides in water. identity of element pH of the chloride in water X Y Z . (ii) Write balanced chemical equations to show how oxide of Y reacts with both hydrochloric acid and calcium hydroxide. [4] [Total: 8]

8 © DHS 2015 8872/02 [Turn over 4 Data concerning methanol and two of its analogues are given in the table below. compound Mr atomic radius of Z in CH3ZH / nm dipole moment / D boiling point / C pKa (pKa = –log10Ka) CH3OH 32.0 0.073 1.7 65 15.5 CH3SH 48.1 0.102 1.5 6 10.4 CH3SeH 95.0 0.116 1.3 25  5 No calculation is required. (a) Explain the differences in boiling points of the three compounds. [3] (b) Arrange the three compounds in order of decreasing acidity and suggest a reason for this trend. [2] (c) When each of the three compounds has dissolved, each molecule is surrounded by water molecules. Draw simple diagrams to show how a water molecule interacts with a CH 3SH molecule and with a CH 3OH molecule. Label each diagram to show the type of interaction involved. CH3SH CH 3OH [2] [Total: 7]

9 © DHS 2015 8872/02 [Turn over 5 Three important natural–occurring compounds used as flavourings in the food industry are shown below: A B C (a) Describe two chemical tests which can be used to distinguish the three compounds. [3] (b) Give two reasons to explain whether compound C can exhibit geometric isomerism. [2]

10 © DHS 2015 8872/02 [Turn over (c) Carvone can be converted to a common precursor D in a two–step synthesis for the making of synthetic flavourings. CH3 O CH3 Br Br Compound D State the reagents and conditions for each step and give the structure of the intermediate in the synthesis of D. CH3 O CH3 Br Br CH3 O CH3 CH2 [3] [Total: 8]