2019 JPJC Prelim H2 Chem P3 QP

 Jurong Pioneer Junior College [Turn Over NAME CLASS 18S JURONG PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2019 CHEMISTRY 9729/03 Higher 2 Paper 3 Free Response 23 September 2019 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper Cover Page for Answer Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams, graphs. Do not use staples, paper clips, glue or correction 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 together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 14 printed pages.

2  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 Section A Answer all the questions in this section. 1 (a) When a redhot wire is plunged into separate samples of the gaseous HCl and HI, a colour change was observed in one of the samples. Suggest which sample gave the colour change. Use data from the Data Booklet to explain your answer. [2] (b) Chlorine gas can be prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide. Manganese (II) chloride a nd water are also formed. Chlorine gas evolved is passed through a drying agent. (i) Write an ion electron equation for the reduction of manganese (IV) oxide, MnO2. [1] (ii) The standard reduction potential, E, of the half–reaction in (b)(i) is +1.23 V. Calculate G, in kJ mol 1, for the overall reaction and use it to explain why the reaction is unlikely to occur. [3] (iii) Give two possible reasons why the reaction does occur. Explain your answer. [2] (c) Alkenes or alcohols can react with gaseous HCl to form alkyl chlorides. However, carboxylic acids do not react with gaseous HCl. (i) Describe the mechanism for the reaction of propene with HCl. [2] (ii) With reference to your mechanism in (c)(i), suggest how propene can act as a BronstedLowry base. [1] (iii) State the type of reaction that occurs between ethanol and gaseous HCl. [1] (iv) Explain why ethanoic acid does not react with gaseous HCl. [1]

3  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 [Turn Over (d) HCl can be used to prepare perchloric acid, HClO4. In the presence of HC lO4, alcohols reacts with nitriles to form N–alkylamides. This is known as the Ritter reaction, as shown in Fig. 1.1. Fig. 1.1 Consider the following reaction which employs the Ritter reaction in the last step. Fig. 1.2 Suggest appropriate reagents and conditions necessary for step s 1 and 2, and draw the structures of the compounds A and B. [4] (e) Lingzhi (Ganoderma lucidum) is a mushroo m that has been used in Chinese medicines for more than 2000 years due to its numerous health benefits. When Lingzhi is ingested, gastric juice in the st omach which comprises mainly hydrochloric acid, activates digestive enzymes to breakdown proteins into smaller peptides and amino acids. (i) A peptide, isolated from Lingzhi, consists of 10 ami no acid residues. It is partially hydrolysed into the following tripeptides: alavalser, leuglyval, serglyarg, valalaval, argasnleu, glyargasn Suggest the primary structure of this peptide. [1] (ii) Histidine is an amino acid also found in Lingzhi. Both Na and Nb are sp2 hybridised. By considering the hybridisation state and the orientation of the p orbitals of the two nitrogen atoms, explain why Na is a stronger base than Nb. [1]

4  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 Histamine, which causes allergic reaction such as runny noses and itchy eyes, is synthesised in the body by decarboxylation of histidine with the aid of an appropriate enzyme catalyst. Fig. 1.3 (iii) With the aid of a Boltzmann distribution curve, explain how enzymes speed up the decarboxylation reaction. [3] (iv) The reaction in Fig 1.3 has a firstorder kinetics. Sketch a graph to illustrate the relationship between the rate of reaction and [histidine] in the presence of a very small amount of enzyme catalyst. [1] [Total: 23]

5  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 [Turn Over 2 (a) The kinetic theory of gases makes assumptions about the behaviour of an ideal gas. State two assumptions of the kinetic theory of gases. [2] (b) Ozone, O 3, is produced naturally in the stratosphere when highly energetic solar radiation strikes molecules of oxygen, O2. 3 O2(g)  2 O3(g) value of Kp = 6.1  1062 at 25 C (i) Write Kp expression for this reaction. [1] (ii) Assuming gaseous oxygen and ozone obey the ideal gas equation, use your answer in (b)(i) to express Kc in terms of Kp and hence, show that the value of Kc is 1.5  1055. [2] (iii) Based on the numerical value of Kc given in (b)(ii), how does th e amount of product compare to the amount of reactant in this reaction at equilibrium? [1] (iv) If a 4 dm 3 flask is initially filled with 10.0 moles of O 2, calculate the equilibrium concentration of ozone. You may use your conclusion in (b)(iii) to make s uitable approximation in your calculations. [2] (c) Ozone reacts with water and sulfur dioxide, SO 2 to form sulfuric acid, H 2SO4, as the only product. (i) Construct a balanced equation for this reaction. [1] H2SO4, a dibasic acid, dissociates in two stages. H2SO4 + H2O  HSO4 + H3O+ HSO4 + H2O  SO42 + H3O+ Ka = 0.012 mol dm3 (ii) Suggest a reason for the difference in the extent of dissociation of H 2SO4 and HSO4. [1] (iii) Calculate the pH of the buffer solution formed when 5 cm3 of 0.100 mol dm3 HCl solution was added to 10 cm3 of 0.200 mol dm3 Na2SO4 solution. [2]

6  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 (d) Concentrated sulfuric acid can be used to form ester by reac ting alcohol with ethanoic acid. However, under the same condition, phenol cannot react with ethanoic acid to form ester E. Fig. 2.1 Explain why ester E cannot be formed from phenol and ethanoic acid. Suggest suitable reagent and conditions for the formation of ester E from phenol. [2] (e) Fig. 2.2 shows the reaction scheme for the conversion of a diester into salbutamol, a drug used to treat asthma. Fig. 2.2 (i) Draw the structure of F. [1] (ii) Isotopic labelling experiment is oft en used to elucidate the mechanism of organic reaction. In step 2 of Fig 2.2, the water used in the hydrolysis of F was labelled using the oxygen isotope 18O. Draw the structure of G, stating clearly the 18O isotope if present. [2] (iii) Suggest the reagent and conditions necessary for step 3. [1] (iv) Suggest why step 2 cannot be carried out before step 1. [1] (v) Explain why the reaction in step 3 is likely to give a low yield of salbutamol. [1] [Total: 20]

7  Jurong Pioneer Junior College 9729/03/J2 PRELIMINARY EXAM/2019 [Turn Over 3 (a) (i) Write the full electronic configurations for a Cr atom. [1] (ii) Transition elements exhibit a range of different oxidation states. Describe and explain the pattern of maximum oxidation states for the elements from Sc to Zn. [2] (iii) Explain why iron( III) salts are usually coloured while scandium( III) salts are white or colourless. [3] (iv) When a solution of cobalt(II) sulfate is warmed with potassium ethanedioate, K2C2O4, sulfuric acid and hydrogen perox ide, a complex with the formula K3[Co(C2O4)3] is formed. The structu