Basic Units, Acidity and Alkalinity Measurements

1. Basic Units, Acidity and Alkalinity Measurements WQT 134 Aquatic Chemistry II Standard Methods 20th ed #1050 Units Standard Methods 20th ed #2310 Acidity Standard Methods 20th ed #2320 Alkalinity Lecture 2

2. Week 2 Objectives Reading assignment: American Public Health Association (APHA), American Water Works Association (AWWA) & Water Environment Federation (WEF). 1999.  Standard Methods for the Examination of Water and Wastewater, 20th edition • Understand basic units and rounding. 2. Understand the role of acidity in water and waste water 3. Understand how to measure acidity (SM #2310) 4. Understand the role of alkalinity in water and waste water 5. Understand how to measure alkalinity (SM #2320)

3. Basic Units and Rounding WQT 134 Environmental Chemistry II STM. 20th edition. #1050

4. _________ is defined as the number of equivalents of solute dissolved in one liter of solution. • Normality • Molarity • Alkalinity • Acidity

5. Basic Units % to mg/L REMEMBER: 1 ppm = 1mg/L

6. In the water treatment field, mg/L and ppm are considered to be equivalent units. • True • False

7. % to Mg/L Word Problems You can memorize or set up a ratio. Its your choice Rule 1. to convert mg/L (ppm) to % multiply by 0.0001 Rule 2. to convert % to mg/L (ppm) multiply by 10,000 Rule 3. Ratio for percent to mg/L:

8. % to Mg/L Word Problems Example 1. Convert 0.55% to mg/L Step 1. Show formula Step 2. Set up ratio Step 3. Cross multiply Step 4. Solve for variable Final Step . Are units correct? Step 1 Step 2 Step 3 Step 4

9. % to Mg/L Word Problems Example 2. Convert 2,000 mg/L to percent Step 1. Show formula Step 2. Set up ratio Step 3. Cross multiply Step 4. Solve for variable Step 5. Reduce Fraction Final Step. Solve….Are units correct? Step 1 Step 2 Step 3 Step 4 Step 5

10. Basic Rounding WQT 134 Environmental Chemistry II STM. 20th edition. #1050

11. Rounding Rules Rule 1. When multiplying or dividing round the result of a calculation to the least # of sig figs present in the original calculation. Rule 2. When adding or subtracting round the result of a calculation to the # that has the fewest decimal places on the original calculation.

12. Rounding Problems Rule #1 Example 1. 56 X 0.003 X 462 X 43.22 = 1.684 Step 1. Solve= 4.975 Step 2. Round = 5.0; because 56 has only 2 sig figs. Rule #2 Example 2. 0.0072+ 12.02+4.0078+25.9+4886 = Step 1. Solve= 4927.9350 Step 2. Round = 4928; because 4886 has no decimal places

13. Acidity WQT 134 Environmental Chemistry II STM. 20th edition. #2310

14. Acidity Experimental Design Part 1 Determine Normality of Sodium Hydroxide Part 2 Titration to pH 8.3 endpoint Part 3 Potentiometric titration curve to pH 9.0 (more data=good) 0.02 N NaOH pH Met4er stir bar 200 ml of sample + 5 drops Phenolphthaleinindicator stir plate

15. Acidity Data Analysis

16. Acidity #2310 • What is Acidity? • Quantitative capacity to react with a strong base to a designated pH. It’s the base neutralizing capacity of a water sample! • Why do we care? • Acids contribute to corrosiveness and influence chemical reaction rates, chemical speciation, and biological processes

17. Acidity #2310 • Why is it important in wastewater industry? • Commonly done to assess performance of a wastewater anaerobic digestor: • A ratio of 10:1 acidity to alkalinity = good digestor, • A ratio 5:1 ratio= bad digestor. • Why is it important in water industry? • Commonly done to determine how much base is needed to buffer the source water.

18. Acidity #2310 • What are some interferences in procedure? • Dissolved gases may be lost or gained during sampling, storage, or titration. Impacts calculation • Oily matter, suspended solids, precipitates, on electrode • Presence of ferrous or ferric iron, aluminum, and manganese may cause drifting end points. • Turbidity • Residual free available chlorine in the sample may bleach the indicator (remove with sodium thiosulfate).

19. Acidity #2310 Calculations and Formulas? Step 1 Calculate Normality of NaOH. Calculate normality of NaOH: Normality = A X B 204.2 X C A = g KHC8H4O4 weighed into 1-L flask (should be 10 g), B = mL KHC8H4O4 solution taken for titration, and C = mL NaOH solution used (should be 50 ml). Use the measured normality in further calculations; 1 mL = 1.00 mg CaCO3.Dissolved

20. Acidity #2310 Calculations and Formulas? Step 2 Determine Acidity Acidity CaCO3/L= (A X B) X 50,000 ml of sample A = mL NaOH titrant used, B = normality of NaOH, Report pH of the end point used, as follows: ‘‘The acidity to pH _______ = _______ mg CaCO3/L.’’

21. Acidity #2310 • Tips and Suggestions? • Use ample sample volume (200 ml); its trial and error • Add NaOH slowly! • Keep track of NaOH added each time! • If pH wont stabilize take reading at fixed interval • Use pH 7 first then pH 4 for calibration • Make first measurements with calibrated probe using pH 4 or pH s7olution • After 25 measurements always check probe drift by reanalyzing pH 4 or 7 solution

22. Alkalinity WQT 134 Environmental Chemistry II STM. 20th edition. #2320 Ca, Mg, Na hydroxides bicarbonate carbonate Total alkalinity = [HCO3-] + 2[CO3-2] + [OH-] – [H+1] [ ] = moles per liter

23. Alkalinity Experimental Design Part 1 Standardization of Titrant (Sulfuric acid)=purchased from Hach! Part 2 Titration for Total Alkalinity determine p alkalinity determine T Alkalinity mg/L as CaCO3/L pH above 8.3 = P alkalinity color change 0.02 N Sulfuric acid P alkalinity 200 ml of sample + 5 drops Phenolphthaleinindicator no color change Palkalinity =0 or titrate to pH 8.3 Blue Color change after addition of Bromcresol green/methyl red pH 4.5 = T alkalinity red color change endpoint T alkalinity + 5 drops Mixed bromcresol green-methyl red titrate to pH 4.5 pH Met4er stir bar stir plate

24. Alkalinity Data Analysis

25. Alkalinity #2320 • What is Alkalinity? • The ability to resist changes in pH is buffering intensity • Alkalinity is a function of carbonate, bicarbonate, and hydroxide content.Quantitative capacity to react with a strong acid to a designated pH. It’s the acid neutralizing capacity of a water sample! • Why do we care? • Used to assess irrigation water quality and water and waste water processes.

26. Alkalinity #2320 • Why is it important in wastewater industry? • Commonly done to assess performance of a wastewater anaerobic digestor: • Properly operating anaerobic digesters typically have supernatant alkalinities in the range of 2000 to 4000 mg calcium carbonate (CaCO3)/L. • Digestor upset • Why is it important in water industry? • Flocculation Coagulation (34.2 mg/L Alum dose needs 17 mg/L alkalinity) • Gives a feel for SMCL for drinking water.

27. Alkalinity #2320 • What are some assumptions in procedure? • hydrogen ions do not exist as a major component • carbonate is half titrated at the phenolphthalein endpoint • carbonic acid (H2CO3) is the major species remaining in solution at the methyl orange endpoint (pH 4.3). • precision (STDEV = 200 mg/L DI water or Real water =1000 mg/L)

28. Alkalinity #2320 • What are some interferences in procedure? • Variable sample volume that requires a procedural trial and error • Analyze quickly within a few hours of sample collection • Soaps, oily matter, suspended solids, or precipitates may coat the glass electrode and cause a sluggish response. • Allow additional time between titrant additions to let electrode come to equilibrium or clean the electrodes occasionally. • Do not filter, dilute, concentrate, or alter sample.

29. Alkalinity #2320 Calculations and Formulas? Step 1 Calculate Normality of H2SO4. Normality = A X B = __________ N sulfuric acid C A = mL of Na2CO3 solution (should be 20 ml) B = Normality of the Na2CO3 solution (should be 0.02N ml) C = mL of Standard sulfuric acid acid read from the burette.

30. Alkalinity #2320 Calculations and Formulas? Step 2 Determine P alkalinity P Alkalinity mg/L as CaCO3/L= (ml of acid to 8.3 or colorless )(Normality)(50 mg/meq as CaCO3)(1000 ml) ml of sample titrated Step 3 Determine T alkalinity T Alkalinity mg/L as CaCO3/L= (ml of acid to 8.3=colorless+ ml to reach pH 4.5=pink)(Normality)(50mg/meq CaCO3)(1000 ml) ml of sample titrated

31. Alkalinity #2320 • Tips and Suggestions? • Use ample sample volume (200 ml); its trial and error • Add H2SO4 slowly! • Keep track of H2SO4added each time! • Rely solely on indicators or can use pH probe!

32. Which laboratory test is concerned with indicator changes at pH 8.3 and about pH 4.5? a. total hardness b. pH c. alkalinity d. total chlorine residual

33. _________ is the measure of how much acid can be added to a liquid, without causing a great change in pH. • Alkalinity • Hardness • pH • Acidity

34. When operating a surface water plant, which laboratory tests are most significant for establishing dosages for coagulation? a. pH and alkalinity b. sulfates c. calcium and magnesium d. total hardness

35. A test that is commonly performed to monitor the treatment process is : • pH • Alkalinity • Turbidity • All of the above

36. Alkalinity is reported as: • Hardness • Softness • mg/l of calcium carbonate • Milliliters of sulfuric acid titrated

37. What piece of laboratory glassware is used mainly to mix chemicals and measure approximate volumes? • Buret • Pipet • Graduated cylinder • Beaker

38. Alkalinity is titrated to the Bromo cresol green methyl red indicator endpoint which is equivalent to this pH. • 4.5 • 5.5 • 3.0 • 6.5

39. Alkalinity is defined as the ___________ capacity of a water. • Buffering • Acid Neutralizing • All of the Above

40. Alkalinity is reported as: • Hardness • Softness • mg/l of calcium carbonate • Milliliters of sulfuric acid titrated

41. Alkalinity and hardness are both analyzed by adding a known reagent to the sample. This process results in a ______ change. Color

42. Alkalinity is defined as the ___________ capacity of a water. Buffering Acid Neutralizing

43. The pH is a measure of the concentration of _____ ____ in a solution. • Hydrogen ions • Hydrozide ions • Acid equivalents • Base equivalents

44. Minerals that cause an increase in alkalinity are: a. calcium carbonate and magnesium bicarbonate b. calcium sulfate and sodium bisulfate c. sodium chloride and ferrous oxide d. magnesium sulfate and calcium chloride

45. An effective chemical to raise pH is: a. alum b. calcium chloride c. polyphosphate d. caustic soda

46. Calculations For Bicarbonate, Carbonate, and Hydroxide P = phenolphthalein alkalinity T = total alkalinity

47. Fine the P, total bicarbonae, carbonate and hydroxide alkalinity for a water sample with the following characteristics based on titration results: a. alum b. calcium chloride c. polyphosphate d. caustic soda