Students are requested, in their own interests, to write legibly.

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1 School of Chemistry UNIVERSITY OF KWAZULU-NATAL, WESTVILLE NOVEMBER 2008 APCH221: CHEMISTRY & INDUSTRY DURATION: 3 HOURS TOTAL MARKS: 100 Internal Examiner: Mr A Bissessur External Examiner: Dr D H Pienaar 1. This paper consists of 18 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 Student Number: much information as possible. Seat Number: SURNAME AND INITIALS (Optional): SIGNATURE: Question TOTAL (25) (25) (25) (25) Internal Marks 100 External Marks 100 Students are requested, in their own interests, to write legibly.

2 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

3 Page 3 QUESTION 1 25 MARKS a) Explain why communication skills in industry, as in much of life, is of paramount importance. Highlight four key issues that addresses the above mentioned statement. (8)

4 4 Page 4 QUESTION 1 (Continued) b) Explain (from an economic standpoint) why it is regarded a mistake to consider the major product as the only product when a manufacturing company considers starting a new manufacturing plant. (5)

5 5 Page 5 QUESTION 1 (Continued) c) The two guiding principles that must hold true for the changes that take place during a chemical reaction are, energy and mass balance. Explain the importance of these two principles. (i) Energy balance (2) (ii) Mass balance (2) d) Consider the manufacture of sulphuric acid by the Contact Process. In Stage 2: catalytic conversion 2SO 2 (g) + O 2 (g) 2SO 3 (g) H o = -197 kj mol -1 (i) If you apply Le Chatelier s principle to the above reaction, indicate which two factors would lead to an increase in production of 2SO 3 (g). Factor 1: (1) Factor 2: (1) (ii) Theoretically the above two factors should be employed to increase yield of the final product however in practice, it is not. Explain? (3)

6 6 Page 6 QUESTION 1 (Continued) (iii) Consider the Block Diagram of the Contact and answer the question that follows: Fig. 1. Manufacture of Sulphuric by the Contact Process Explain, using equations, the chemical process that occurs in the Oleum Tower shown in the block diagram above. (3)

7 7 Page 7 QUESTION 2 25 MARKS a) The reaction between nitrogen and hydrogen in the Haber Process (block diagram shown below) involves an equilibrium: N 2 (g) + 3H 2 (g) 2NH 3 (g) Fig. 2. Block diagram of the Haber Process (i) What are the 3 main stages of the Haber Process? (3) (ii) Explain how the CO 2 from the re-forming stages is removed and the importance of its removal. (2)

8 8 Page 8 QUESTION 2 (Continued) b) Graph of how percentage conversion of ammonia varies with temperature Fig.3. The way the equilibrium proportion of ammonia varies with temperature. (i) What does the above graph indicate about the yield, in terms of theoretical temperature and pressure that should be applied? (2) (ii) Indicate, with suitable reasons, which physical conditions (in terms of temp and pressure) are most condusive to producing the best possible yield. (4)

9 9 Page 9 QUESTION 2 (Continued) c) Consider the production of Nitric acid by the Ostwald Process: (i) Give three equations (need not be balanced but show physical states of reactants and products) which outlines the manufacture of nitric acid (HNO 3 ) by catalytic oxidation. Stage 1- Equation: (2) Stage 2- Equation: (1) Stage 3- Equation: (2) (ii) Indicate how the yield of the major product at stage 2 (in (i) above) is optimized (increased) given the reaction conditions that prevail from stage 1. (2)

10 10 Page 10 QUESTION 2 (Continued) d) Study the following Ellingham diagram and answer the questions that follow: Fig. 4. Ellingham diagrams for a number of sulphide compounds

11 11 Page 11 QUESTION 2 (Continued) (i) Explain in detail, using information from the Ellingham diagram provided, on page 9, why the reduction of a sulphide compound e.g. CdS, MnS or FeS by carbon or hydrogen is considered hopeless. (5) (e) The Ellingham diagram shows that, for the reduction of ZnO by CO to produce Zn the temperature is predicted to be approximately 1180 o C. Why is it unwise to assume that the reaction will proceed at this temperature and what necessary step should be taken during the actual reduction reaction? (2)

12 12 Page 12 QUESTION 3 a) Give the four main methods that may be used for the extraction of metals. 25 MARKS (4) b) Zinc is extracted from ZnS. (i) How is ZnS separated from the other ore components? (1) (ii) Give the final products of roasting ZnS with coke at 1400 o C. (2) (iii) How can high purity Zn be produced? (1)

13 13 Page 13 QUESTION 3 (Continued) c) (i) What is the main purpose of cyclones in industry? (1) (ii) What is the function of a hydrocyclone? (1) (iii) Describe in detail the principle of a separation unit operation of a cyclone used in industry. (3) d) Consider the following heat exchanger configuration: Fig. 5. Schematic diagram of a heat exchange configuration

14 14 Page 14 (i) Identify the above configuration (1) QUESTION 3 (Continued) (ii) Explain briefly the operation of this exchanger. (2) e) Name the mine in South Africa which is the only one that is currently producing Fluoroapatite. (1) f) Give two equations for the production of phosphoric acid from phosphorus (P) (obtained from the Thermal or Furnace Process). (2) g) Phosphoric acid produced by the Wet Process is mixed with a by-product, gypsum (CaSO 4.2H 2 O). Explain fully how the desired product phosphoric acid is separated from the gypsum by-product. (3)

15 15 Page 15 QUESTION 3 (Continued) e) Calculate the amount (%) of the three main components (N 2,P 2 O 5,K 2 O) for a South African produced fertilizer designated by the following formulation: (60) Zn (3)

16 16 Page 16 QUESTION 4 25 MARKS a) What is presently the main source of soda ash (sodium carbonate) throughout the world? (1) b) Explain briefly how sodium carbonate in Botswana (called Botswana ash) is manufactured. (2) c) Consider the following Diagram for the production of soda ash Fig. 6. Process flow diagram for the manufacture of Botswana ash (i) Indicate the purpose of the: (A) well field (1)

17 17 Page 17 (B) solar pans (1) QUESTION 4 (Continued) (ii) Explain the chemical process and indicate the product that forms at the carbonation stage. (2) d) Consider SASOL s coal gasification process. B A Fig. 7. Reactor used in SASOL

18 18 Page 18 (i) Name the reactor in which the above start-up process takes place. (1) QUESTION 4 (Continued) (ii) Identify reactants A and B: A that enters at the top of the reactor (1) B that enters from the bottom of the reactor (1) (iii) Indicate with equations all reactions and reaction conditions that occur within the SASOL reactor (shown in figure 7). (6) (iv) Purified synthesis feed gas is converted through SASOL s Fischer-Tropsch (F-T) technologies at high and low temperatures. Give the specific type of the reactor used in: High temp F-T (1) Low temp F-T (1)

19 19 Page 19 QUESTION 4 (Continued) e) In the Pulp and Paper Industry, explain what is: (i) raw pulp (1) (ii) dissolving pulp (2) f) Raw pulp produced by the acid bisulphite process undergoes a five stage bleaching process. Give four functions of these bleaching stages. (4)

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