2019 SAJC H2 Chem Prelim P2 QP

1 NAME Class ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Chemistry (9729) Paper 2 Structured Questions 30 August 2019 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS: Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, 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: Question 1 2 3 4 5 Total Marks 9 8 20 25 13 75 This document consists of 20 printed pages (including this page).

2 1. (a) P, Q, R and S are consecutive elements in Period 4. The table below shows the first four ionisation energies (in kJ mol–1) of the elements. Element 1st I.E. 2nd I.E. 3rd I.E. 4th I.E. 5th I.E. P 908 1730 3828 5980 7970 Q 577 1980 2960 6190 8284 R 762 1540 3300 4390 9020 S 947 1798 2735 4837 6043 (i) Explain why the second ionisation energy of Q is higher than that of R. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [2] (ii) Explain why P is not considered to be a transition metal like most of the d-block metals. ………………………………………………………………………………………. ………………………………………………………………………………………. [1] (b) The idea of covalent bonding was first described in 1916 by an American physical chemist Gilbert Newton Lewis. HCOCl is an example of a polar covalent molecule. (i) Explain what is covalent bonding. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [1]

3 1. (b) (ii) State what is meant by the term polar when applied to a covalent bond. ………………………………………………………………………………………. ………………………………………………………………………………………. [1] (iii) State and explain with reference to the Valence Shell Electron Pair Repulsion theory, the shape of HCOCl molecule. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. [2] (iv) The molecule of HCOCl contains both σ (sigma) and π (pi) bonds. Draw labelled diagrams to show how orbitals overlap to form  a σ (sigma) bond  a π (pi) bond [2] [Total:9]

4 2 Below is a labelled diagram of a hydrogen-oxygen fuel cell in an alkaline electrolyte. (i) Write the half equations for both electrodes and hence the overall equation. Cathode ………………………………………………………………………… Anode …………………………………………………………………………… Overall ………………………………………………………………………..… [2] (ii) Calculate ∆Go for the above reaction and state whether it is spontaneous. [3]

5 2. (a) (iii) The hydrogen -oxygen fuel cell produces 1.5 A of current. Hydrogen gas is contained in a 1 dm 3 tank at a pressure and temperature of 200 atm and 20 oC respectively. Determine the number of days the fuel cell can operate before the hydrogen gas runs out. Give your answer to the nearest whole number. You may assume there is an unlimited supply of O2. [3] [Total:8] 3. Spider silk is a protein fiber. Major amino acids in the silk proteins are alanine and glycine. Serine and glutamine are also present in significant quantities in some types of silk. The table below shows the typical amino acids present in spider silk. Amino Acid Formula of side chain (R in RCH(NH2)CO2H) Glycine –H Alanine –CH3 Serine –CH2OH Glutamine –CH2CH2CONH2 (a) (i) Glycine exists as crystalline solids. Draw the zwitterionic structure of glycine and account for the high melting point of glycine. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [2]

6 3. (a) (ii) Write an equation to show the reaction between alanine and aqueous sodium carbonate. [1] (iii) Suggest a chemical test to distinguish between serine and glutamine. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [2] (b) Natural spider silk has excellent mechanical properties. In a recent study, researchers discovered that graphene-based materials can be used to boost the properties of spider's silk up to three times the strength and ten times the toughness of the unmodified silks. Graphene is the thinnest material known to exist, yet it is stronger than steel. It is made from only carbon and is a single layer of graphite just one atom thick as shown in Figure 3.1 below. Figure 3.1

7 3. (b) (i) With reference to structure and bonding, explain why graphene is strong. [1] ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (ii) Since its discovery in 2004, graphene has been widely studied and manufactured as replacement materials for many touchscreen products. Suggest why graphene is a suitable touchscreen material in mobile phones. [1] ……………………………………………………………………………………… ……………………………………………………………………………………… (c) Spider makes an excellent treat for a colony of marauding ants. To protect their homes, spiders coat their webs using a chemical called 2-pyrrolidone, which acts as a deterrent to many insects. 2-Pyrrolidone is a 5-membered cyclic amide (commonly known as lactam). It is a colourless liquid that is miscible with water and most common organic solvents. 2-Pyrrolidone

8 3. (c) 2-pyrrolidone can be synthesised using 3-chloropropan-1-ol as the starting organic compound as shown in the reaction scheme below: (i) State the type of reaction in Step V. ……………………………………………………………………………………… [1] (ii) Suggest reagents and conditions for Step I, II and III. Step I : ………………………………………………………………… Step II : ………………………………………………………………… Step III : ………………………………………………………………… [3] (iii) Draw the structures of intermediate compounds A and B. [2] A B

9 3. (c) (iv) With the aid of an equation, explain why anhydrous condition is necessary for the reaction in Step IV. [1] ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (v) 2-pyrrolidirol can be synthesised from 2-pyrrolidone. 2-pyrrolidirol Deduce whether 2-pyrrolidone or 2-pyrrolidirol has a higher pKb. ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… [2] (vi) Suggest a synthesis of 3-chloropropan-1-ol from 1,3-butandiol. 1,3-butandiol [4] [Total:20]

10 4 (a) Copper and iron are examples of native metals, which are found pure in its metallic form on its own or in alloys in nature. Copper and iron form many complexes with a range of colours as shown in the table: complex colour complex colour [Cu(NH3)4]2+ dark blue [Fe(H2O)6]3+ yellow [Cu(H2O)6]2+ blue [Fe(CN)6] 3− red (i) Explain why [Cu(H2O)6]2+ is blue. [3] …………………………………………………………………………………… …………