MODULE 2 ASSIGNMENT
ENVM 585: WATER AND WASTEWATER TREATMENT
Module 2: WATER QUALITY
Each question is worth 10 points. Show calculations.
1. The reaction of soda ash (Na2CO3) with calcium sulfate in water is represented by the following chemical reaction: Na2CO3 + CaSO4>>> CaCO3 + Na2SO4. Assuming that this reaction is complete and that there is 153 mg/l of CaSO4 initially present, what is the mass of soda ash that must be added to 1 liter of the water?
2. How many grams of CaO are required to be the chemical equivalent of 246 g of Mg(HCO3)2?
3. A 100-ml sample of water is titrated with 0.02 N H2SO4. The initial pH is 9.5, and 6.2 mL of acid is required to reach the pH 8.3 endpoint. An additional 9.8 mL is required to reach the 4.5 endpoint. Determine the species of alkalinity present and the concentration of each species.
4. Draw a milliequivalent-per-liter bar diagram and determine the error in the ion balance for the water with the following ion concentrations;
Cation, mg/L Anion, mg/L
Ca2+ = 60 HCO3- = 115
Mg2+ = 10 SO42- = 96
Na+ = 7 NO3- = 10
K+ = 20 Cl- = 11
5. Would hard water be acceptable in most drinking-water supplies? Why or why not? Would hard water be an acceptable coolant for an industrial plant? Why or why not?
6. An analysis for BOD5 is to be run on a sample of wastewater. The BOD is expected to range from 50 350, and the dilutions are prepare accordingly. In each case, a standard BOD bottle is used. The data are recorded below. Determine the BOD5 of the wastewater.
Bottle Number Wastewater, mL DOI DO5
1 20 8.9 1.5
2 10 9.1 2.5
3 5 9.2 7.5
4 2 9.2 7.5
DOI is the initial dissolved oxygen
DO5 is the dissolved oxygen at the end of the test
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