TJC_H1_CHEM_P2_(B)_QN

12 2015 TJC H1 Chemistry Preliminary Exam [Turn Over Section B Answer two questions from this section on separate answer paper. 5 (a) Hydrogen sulfide is a colourless gas with a characteristic ‘rotten egg’ smell. It occurs naturally in crude petroleum and reacts with methane according to the following equilibrium. CH4(g) + 2H2S(g) CS2(g) + 4H2(g) H = +232 kJ mol-1 (i) State and explain the effect on the number of moles of methane when the volume of the vessel is reduced at a constant temperature. (ii) Write an expression for the equilibrium constant, Kc, stating its units. (iii) In an experiment, 1.00 mol of CH 4, 2.00 mol of H 2S, 1.00 mol of CS 2 and 2.00 mol of H 2 are mixed in a 250 cm3 vessel at 960 °C. The concentration of methane is found to be 5.56 mol dm-3 when the system reaches equilibrium. Calculate the value of Kc at 960 °C. (iv) The equilibrium constant varies with temperature according to the van’t Hoff equation: 𝑙𝑛 𝐾2 𝐾1 = − ∆𝐻𝑜 𝑅 ( 1 𝑇2 − 1 𝑇1 ) where K1 is the equilibrium constant at temperature T1 K2 is the equilibrium constant at temperature T2 Ho is the enthalpy change in J mol-1 R is the ideal gas constant and T is temperature in Kelvin. Using your answer in (iii), calculate the value of equilibrium constant at 480 °C. (v) Hydrogen sulfide can be removed by passing it through nitric acid. 0.15 mol of H 2S was found to react with 0.10 mol of HNO3 to give sulfur and an oxide of nitrogen. Determine the oxidation state of nitrogen in the oxide. Hence, write a balanced equation fo r the reaction of H2S and HNO3. [10] (b) Adipic acid is one of the most important dicarboxylic acids and has a wide range of industrial applications. It is used as a monomer in the synthesis of nylon, and in the production of plasticizer and coatings. adipic acid cyclohexanone

13 2015 TJC H1 Chemistry Preliminary Exam [Turn Over (i) Predict and explain the difference in boiling points of adipic acid and cyclohexanone. (ii) Show a three -step synthetic route to obtain adipic acid from cyclohexanone. Suggest reagents and conditions you would use and s how the structures of any intermediates formed. (iii) Suggest a simple chemical test to distinguish between adipic acid and cyclohexanone. State the observations and write a balanced equation for any reaction that occurs. In the 1880s, German chemist Rainer Ludwig Claisen discovered that esters were able to react in the presence of a strong base to give a keto ester. (iv) Name the type of reaction that has taken place between the ester molecules. (v) Two molecules of an ester undergo the above reaction to give methanol and the following organic product. Suggest the structure of the ester. [10] [Total: 20]