EHS 429 MAIN EXAMINATION PAPER 2018 DECEMBER QUESTION ONE (25 marks and compulsory, i.e., must be answered) The table below shows the results of water quality analysis of a sample of raw water intended for potable water treatment. Using the data provided in the table as well as the chemical equations and equilibrium constants provided below, answer the following questions (5 marks for each question). i. ii. iii. iv. V. Check the water quality analysis results for consistency and suggest if the analysis results are acceptable. Calculate the bicarbonate and permanent hardness in mg/L of CaCO3 Draw the ion bar chart of the raw water in meq/L Calculate the lime (in mg/L as CaCO3) required to soften this water using excess lime treatment method. Calculate the soda ash required (in mg/L as CaCO3). Parameter Unit Concentration Molecular (mg/L) weight TDS mg/L 300 Ca mg/L 65 40.1 ++ Mg mg/L 20 24.3 Na+ mg/L 15 23 K* mg/L 5 39.1 HCO3 mg/L 200 61 SO4 mg/L 120 96.1 cr mg/L 25 35.5 EX H2CO3 pH mg/L 20 62 pH units 7.2 Chemical equations and equilibrium constants a. Neutralisation of carbonic acid: CO2 + Ca(OH)2 ↔ CaCO3(s) + H₂O b. Precipitation of carbonate hardness due to calcium Ca(HCO3)2 + Ca(OH)2 ↔ 2CaCO3 + 2H₂O Page 2 of 8

EHS 429 MAIN EXAMINATION PAPER 2018 DECEMBER QUESTION ONE (25 marks and compulsory, i.e., must be answered) The table below shows the results of water quality analysis of a sample of raw water intended for potable water treatment. Using the data provided in the table as well as the chemical equations and equilibrium constants provided below, answer the following questions (5 marks for each question). i. ii. iii. iv. V. Check the water quality analysis results for consistency and suggest if the analysis results are acceptable. Calculate the bicarbonate and permanent hardness in mg/L of CaCO3 Draw the ion bar chart of the raw water in meq/L Calculate the lime (in mg/L as CaCO3) required to soften this water using excess lime treatment method. Calculate the soda ash required (in mg/L as CaCO3). Parameter Unit Concentration Molecular (mg/L) weight TDS mg/L 300 Ca mg/L 65 40.1 ++ Mg mg/L 20 24.3 Na+ mg/L 15 23 K* mg/L 5 39.1 HCO3 mg/L 200 61 SO4 mg/L 120 96.1 cr mg/L 25 35.5 EX H2CO3 pH mg/L 20 62 pH units 7.2 Chemical equations and equilibrium constants a. Neutralisation of carbonic acid: CO2 + Ca(OH)2 ↔ CaCO3(s) + H₂O b. Precipitation of carbonate hardness due to calcium Ca(HCO3)2 + Ca(OH)2 ↔ 2CaCO3 + 2H₂O Page 2 of 8

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