INSTRUMENTATION: Titration - CAS Lab

1 METHOD #: for NPDES (Editorial Revision 1978)TITLE:Alkalinity (Titrimetric, pH )ANALYTE:Alkalinity INSTRUMENTATION: TitrationSTORET and method is applicable to drinking, surface, and saline waters, domestic andindustrial method is suitable for all concentration ranges of alkalinity; however,appropriate aliquots should be used to avoid a Titration volume greater than titrimetric analysis is of unaltered sample is titrated to an electrometrically determined end point ofpH The sample must not be filtered, diluted, concentrated, or altered inany sample should be refrigerated at 4 C and run as soon as practical. Do notopen sample bottle before , such as salts of weak organic and inorganic acids present in largeamounts, may cause interference in the electrometric pH samples having high concentrations of mineral acids, such as mine wastesand associated receiving waters, titrate to an electrometric endpoint of pH ,using the procedure in:Annual Book of ASTM Standards, Part 31, "Water", p115, D- 067, Method D, ( 1976).

2 And grease, by coating the pH electrode, may also interfere, causingsluggish meter or electrically operated titrator that uses a glass electrode and can beread to pH units. Standardize and calibrate according to manufacturer'sinstructions. If automatic temperature compensation is not provided, maketitration at 25 2 an appropriate sized vessel to keep the air space above the solution at aminimum. Use a rubber stopper fitted with holes for the glass electrode,reference electrode (or combination electrode) and stirrer, pipets, flasks and other standard laboratory , Pyrex 50, 25 and 10 carbonate solution, approximately N: Place g (to nearestmg) Na CO (dried at 250 C for 4 hours and cooled in desiccator) into a 1 liter23volumetric flask and dilute to the acid (sulfuric or hydrochloric), N: Dilute mL conc H SO or conc HCl to 1 liter with distilled water.

3 Standardize versus mL of Na CO solution with about 60 mL distilled water by titrating23potentiometrically to pH of about 5. Lift electrode and rinse into beaker. Boilsolution gently for 3-5 minutes under a watch glass cover. Cool to roomtemperature. Rinse cover glass into beaker. Continue Titration to the pHinflection point. Calculate normality using:where:A = g Na CO weighed into 1 liter23B = mL Na CO solution23C = mL acid used to inflection acid (sulfuric or hydrochloric), N: Dilute mL of Nstandardacid to 1 liter with distilled water. Standardize by potentiometrictitration of mL Na CO solution as above. a sufficiently large volume of titrant ( > 20 mL in a 50 mL buret) toobtain good precision while keeping volume low enough to permitsharp end < 1000 mg CaCO /L use N > 1000 mg CaCO /L use N preliminary Titration is sample in flask by pipetting with pipet tip near bottom of pH of standard acid ( or ), being careful to stir thoroughly butgently to allow needle to obtain to pH Record volume of Titration of low alkalinity of <20 mg/L titrate 100-200 mL as above ( ) using a 10mL microburet and N acid solution ( ).

4 Titration at pH in range of , record volume and exact carefully add titrant to lower pH exactly pH units and recordvolume. Titration to pH :A = mL standard acidN = normality standard Titration of low alkalinity:where:B = mL titrant to first recorded pH C = total mL titrant to reach pH units lower N = normality of and analysts in seventeen laboratories analyzed synthetic water samplescontaining increments of bicarbonate, with the following results:Increment asPrecision asAccuracy asAlkalinityStandard DeviationBias,Bias,mg/liter, CaCOmg/liter, CaCO%mg/L, + + + + (FWPCA Method Study 1, Mineral and Physical Analyses) a single laboratory (EMSL) using surface water samples at an averageconcentration of 122 mg CaCO /L , the standard deviation was Methods for the Examination of Water and Wastewater, 14th Edition, p 278,Method 403, (1975).

5 Book of ASTM Standards, Part 31, "Water", p 113, D-1067, Method B, (1976).