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

Transcription

1 School of Chemistry UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CAMPUS JUNE 2008 EXAMINATION APCH211: ENVIRONMENTAL CHEMISTRY DURATION: 3 HOURS TOTAL MARKS: 100 Internal Examiner: Dr J C Ngila External Examiner: Professor O J Okonkwo Tshwane University of Technology IMPORTANT: COMPLETE THIS SECTION IMMEDIATELY SURNAME AND INITIALS (Optional): SIGNATURE: Student Number. Seat No. INSTRUCTIONS 1. Calculators may be used for calculations but all working must be clearly shown, where applicable. 2. You must write legibly in Black or Blue Ink. Pencils and Tipp-Ex are not allowed. 3. Your ANSWERS must be written on the question paper in the spaces provided. You may use the space overleaf for rough work. 4. This paper consists of 13 pages including a Data Sheet and Periodic Table. ANSWER ALL QUESTIONS Quest Total Internal External Students are requested, in their own interests, to write legibly.

2 Page 2 Question 1 10 marks a) In the determination of total hardness of water, 10 ml of of 0.01 M EDTA was titrated with the 20 ml of the River water sample to an end point with Eriochrome Black T indicator. Calculate the total hardness in River water mg.l -1 in the sample. Suppose the South Africa Bureau of Standards (SABS) guideline value for total hardness is given as 10 ppm CaCO 3, comment on your value. Ca 2+ + EDTA 2- Ca-EDTA (4) b) Explain how pollutants enter and exit the Earth s atmosphere. In your answer, indicate the sources and processes involved. (6)

3 Page 3 Question 2 10 marks a) Briefly describe photochemical smog. Give two effects of smog on the environment. (2) b) Give the sources and health effects of the following elements on humans. (4) i) Dimethyl mercury; (CH 3 ) 2 Hg ii) Polybrominated diphenylether (PBDE) iii) Sulphur dioxide iv) Hydrogen cyanide c) Mariannhill landfill in Pinetown, Kwazulu Natal (KZN), handles waste from different parts of Durban. i) Which parts of KZN does the waste disposed off at Mariannhill landfill come from? What types of pretreatment is the waste subjected to before disposal? (2)

4 Page 4 ii) Give two disadvantages of landfills as the final destination of waste. (2) Question 3 10 marks a) State one advantage and one disadvantage of the following methods for waste treatment. i) Acid/base neutralization (2) ii) Chemical precipitation (2) iii) Oxidation/Reduction (2) iv) Chemical extraction and leaching (2) v) Ion Exchange (2)

5 Page 5 Question 4 10 marks a) A sample of wastewater in Sea Cow Lake in Ethekwini Municipality (KZN) was analyzed and found to contain 5.10 mg.l -1 of organic substances of average structure C 76 H 86 O 50 N 4 S 2 and molecular mass of 1920 g.mol -1. Calculate the total organic carbon (TOC) concentration in parts per million. If the expected level of TOC in wastewater is mg.l -1, comment on your answer. (4) b) Microorganisms are usually used for secondary treatment of wastewater. i) Describe anaerobic biodegradation of phosphate containing pesticide residues and explain the procedure involved. Use a schematic diagram if possible to illustrate your answer. (2)

6 Page 6 ii) Describe the process of wastewater treatment using constructed wetlands (CWLs) and the importance of application of CWLs. (4) Question 5 8 marks a) The following questions apply to greenhouse effect: i) What is a greenhouse gas? (2) ii) List four examples of greenhouse gases. (2) iii) Describe the process of greenhouse effect. (4).

7 Page 7 Question 6 10 marks a) Briefly discuss how each of the following activities contributes to environmental pollution. Give one example of a pollutant in each case. i) Agriculture (2) ii) Mining (2) iii) Transportation (2) iv) Construction (2) v) Deforestation (2) Question 7 12 marks a) The following techniques are used for processing hazardous wastes before long term disposal. Describe the processes giving one example of application in each case. i) Immobilization (2) ii) Stabilization (2)

8 Page 8 iii) Chemical Fixation (2) iv) Solidification (2) b) The following matrices are used for immobilization, stabilization and solidification processes discussed in part (a) above. Briefly describe each matrix and give one example of application in each case. i) Sorbents (1) ii) Thermoplastics (1) iii) Glass (1) iv) Silicates (1)

9 Page 9 Question 8 6 marks a) Give a description of each of the following atmospheric particles (6) Term Meaning i) Condensation aerosol ii) Dispersion aerosol iii) Fog iv) Haze v) Mists vi) Smoke Question 9 12 marks Chemical coagulants are used for removal of suspended particles in water. Stokes Law is used to estimate settling rates of particles in aqueous medium. ν t = (ρ p 2 ρ w )gd p 18μ a) Define the symbols in the Stoke s Law equation and give the SI units for each symbol. (6)

10 Page 10 b) For a spherical particle of clay with diameter of 2 x 10-3 mm (2 x 10-6 m); particle density of 2.65 x 10 3 Kg.m -3, water density of 1.0 x 10 3 Kg.m -3 ; water viscosity of 1.0 x 10-3 Kg.m -1.s -1 and acceleration due to gravity of 9.8 m.s -2. i) Calculate the terminal velocity of the particle described above. (2) ii) Determine how long it would take the particle to settle at the bottom of a 4-meter depth tank. (2) iii) Suppose the detention time in the tank referred to in part (ii) is 1.5 hr, state whether it is possible to remove particles of the above dimensions or not. Justify your answer. (2)

11 Page 11 Question marks Wastewater could be used for drinking purposes after treatment. a) State the main quality requirements for treated water meant for drinking. (4) b) One of the methods utilized for toxicity test on a suspect pollutant use a Dose-Response curve. With the help of a labeled schematic diagram, describe the steps of the procedure used in toxicity test. (4) c) Describe the following parameters applied in toxicity measurement experiments. i) Lethal dose amount 50 = LD 50 (2) ii) Lethal dose concentration 50 = LC 50 (2)