School of Chemistry UNIVERSITY OF KWAZULU-NATAL, WESTVILLE NOVEMBER 2007 EXAMINATION APCH221: CHEMISTRY & INDUSTRY DURATION: 3 HOURS TOTAL MARKS: 100 Internal Examiner: Mr A Bissessur External Examiner: Professor K Bissetty 1. This paper consists of 15 pages. Please make sure you have them all. 2. Answer on the question paper. 3. When reaction equations are required, these must be balanced and include as much information as possible. Students are requested, in their own interests, to write legibly. Student Number: Seat Number: Question 1 2 3 4 TOTAL (25) (25) (25) (25) Internal Marks 100 External Marks 100 1
Page 2 1. This paper consists of 14 pages including the Ellingham Diagram at the back of the paper. Please ensure that you have them all. QUESTION INTERNAL EXTERNAL FINAL 1 (25) 2 (25) 3 (25) 4 (25) TOTAL 100 Students are requested, in their own interests, to write legibly.
Page 3 Question 1 25 marks a) Teamwork is not the norm in the university and research projects are usually individual efforts, with collaboration focused between the student and academic. In industry the opposite is true, explain. (5) b) Explain which economic factors of production must carefully be considered by managers when starting a new manufacturing process. (2) c) Explain the importance of carrying out the following protocols when designing a new plant. (i) an energy balance (2)
Page 4 Question 1 (Continued) (ii) a mass balance (2) d) The following data was extracted from the financial report of a Petrochemical Industry: Capital Cost R500 million Depreciation per annum 15% Return on capital 65% Production @ 100% 10 000 000 L capacity COSTS SUM/ R million Labour 50 Depreciation Raw materials 40 Energy 10 Patents 2 Calculate the price per litre of octane, if the plant was operating at 75% of efficiency level. (5)
Page 5 Question 1 (Continued) e) Given the large and constant demands for a product, chemical industries are designed to work continuously. Briefly discuss outlining the advantages and disadvantages of (i) a continuous chemical process (5) (ii) a batch chemical process (4)
Page 6 Question 2 25 marks Sulphuric acid produced by the Contact process manifests itself in the manufacture of a variety of commercial products. Study the following flow chart and answer the questions that follow: Stage 1 Fig 1. Manufacture of Sulphuric by the Contact Process a) Write an equation for the reaction of the sulfur burner process shown in stage 1, shown in figure 1. (1) b) How much of heat is evolved in stage 1? (1)
Page 7 Question 2 (Continued) c) Describe how the heat of reaction generated in stage 1 is of benefit to the plant. (4) d) Explain the role of the Four Pass Converter in Fig 1 (page 5). (2) e) Write the chemical formula of the catalyst used in the Four Pass Converter. (1) f) Explain, with reasons, the physical set-up of the catalyst. (2)
Page 8 Question 2 (Continued) f) Consider the following block diagram of the Haber Process and answer questions that follow: Figure 2. Block diagram of the Haber Process (i) Describe what happens to the raw material (naphtha or natural gas) before being sent to the Primary reformer. (2) (ii) Explain, using equations what happens in the: (a) Primary reformer (refer Fig. 2 above) (2)
Page 9 Question 2 (Continued) (b) Secondary reformer (refer fig. 2 above) (3) g) The commercial production of nitric acid is referred to as the Ostwald s Process. (i) Identify the raw material indicating its composition and give the reaction conditions that is used in the manufacture of nitric acid. (2) (ii) The 2nd stage of the Ostwald Process involves the following reaction: 2NO 2 (g) + O 2 (g) 2NO 2 (g) H= -114 kj/mol Given the fact that the reaction is capable of going in both directions, explain the implication of this reaction by catalytic conversion and indicate how a high yield of NO 2 may be obtained by controlling the temperature. (3) i) Give the acid concentration of the HNO 3 after Stage 2. (1)
Page 10 j) Explain why the solution in (i) above has to be purified. (2) k) State how it is possible to achieve a concentration of 95% HNO 3. (1) Question 3 25 marks a) List the four major methods that may be applied to extract metals from metal ores. (2) b) Study the Ellingham diagram for a number of sulfides.
Page 11 Figure 3. Ellingham diagram for a number of sulphides. Question 3 (Continued) b) Zinc is extracted from a zinc ore called zinc blende, ZnS. Explain with the aid of the Ellingham diagram why carbon (C) is not used to reduce zinc blende. (4)
Page 12 c) With the aid of equations, describe the extraction of Zn metal from a zinc ore. (5) Question 3 (Continued) d) Indicate the difference in selection of a membrane cell over a mercury cell in the Chlor-Alkali Process in terms of the following: Mercury cell Membrane cell
Page 13 (a) Construction costs (b) Operation of cells (c) Product targeted (4) e) Give three reasons why industrial processes seldom produce products which can be sold without prior purification. (3) f) Explain the use of cyclones for the separation of components in industry (note: principle of separation is not required here). (3) Question 3 (Continued) g) Consider the following heat transfer configurations numbered a e :
Page 14 (i) Identify the type of configuration for a & b. (1) (ii) Explain in detail the use of configurations a & b in industrial processes. (3) Question 4 25 marks
Page 15 a) Phosphoric acid is used as an acidulent in soft drinks. Give the name of the only company in South Africa that mines the mineral apatite for the extraction of phosporus. (1) b) Name the two processes that converts phosphate rock into phosphoric acid. (2) c) Which of the two methods named in (b) above is the preferred method? Give a reason for your choice. (2) d) Explain why urea is commonly used as the main ingredient of most fertilizers. (2) e) The following code which was found printed on a particular fertilizer bag, 2:2:4 (56) Mg. Use the above information to calculate the composition of the fertilizer. (2) Question 4 (Continued)
Page 16 f) Study the following diagram and answer the questions that follow: Figure 5. Reactor used in SASOL (i) Identify the above reactor (fig. 5) used at the start of SASOL s gasification process. (1) (ii) Write an equation for the major reaction occurring n this reactor. (1) (iii) Write two other reactions that occur in this reactor (and name them). (2) Question 4 (Continued)
Page 17 (iv). Describe the Fischer-Tropsch Process at high temperature highlighting the reaction products, advantages and the catalyst used. (5) (v). For the cooking of wood chips to produce pulp, differentiate between the acid bisulfite and the Kraft processing of wood to pulp in terms of: (a) Chemicals used in the cooking process. (3) (b) Reactions conditions. (2) (vi) Indicate the importance of bleaching of raw pulp. (2)