- Standardized sulfuric acid (0.1142 N H2SO4)
- Bromcresol green indicator solution - Dissolve 100 mg bromcresol green in 100 mL of about a 1:1 ethanol/deionized H2O solution.
- Phenolphthalein indicator solution - Dissolve 0.5 g phenolphthalein in 85 mL 95% ethanol and dilute to 100 mL with deionized water.
- Automatic titrator
- 150 mL beakers
- Pour 100 mL of the sample into a 150 mL beaker.
- If free residual chlorine is present, add 1 drop of 1 M Na2S2O3.
- Measure and record pH of solution.
- Place beaker under electrode, stirrer and titration probe.
- If the pH is greater than 8.3 go to step 6.
- If the pH is less than or equal to 8.3, go to step 9.
- (If the pH is 4.5 or less, the alkalinity equals zero.)
- Put 3 drops of the phenolphthalein indicator into the sample. Solution will turn pink.
- Titrate to almost clear. (For set-up of control unit see next page.)
- Control unit will calculate % phenolphthalein alkalinity. Record on record sheet with one decimal.
- Put 5 drops of the bromcresol-green indicator into another 100 mL sample.
- (Solution will turn blue.)
- Titrate to a clear green (no blue or yellow tints).
- Control unit will calculate % total alkalinity. Record on record sheet with one decimal.
- When finished cover electrode hole and turn control unit off.
- Alkalinity, meq/L = (mL acid)(N H2SO4)(1000)/mL sample
- Use the phenolphthalein number in the above equation to calculate the phenolphthalein alkalinity.
- Use the bromcresol-green number in the above equation to calculate the total alkalinity.
Control Unit Settings
- Sample mg = 1000
- pH = 4.5 for total alkalinity
- pH = 8.3 for phenolphthalein alkalinity
- titrant normality = 0.815
Set-Up of Control Unit
- Turn power on. Let unit set-up.
- When ENTER DATE APPEARS press next step. Continue pressing next step until modeappears.
- Enter 1 for mode. Then continue pressing next step until pH calibr.
- Enter Y. Then press next step until Buffer 1 appears.
- Uncover electrode hole. Place electrode in yellow pH 7 solution. Press next step.
- Wait until Buffer 2 appears.
- Rinse electrodes and place in pink pH 4 solution. Press next step.
- When calibrated, rinse electrodes and prepare to run samples.
- Press BALANCE PROGRAM.
- Press Y, then continue pressing next step until SAMPLE 1 MG appears.
- Type in 1000 - next step for each sample. When finished press BALANCE PROGRAM.
- Place sample 1 under electrode and press START.
- Jenkins, S.R., Moore, R. C. January, 1977. A Proposed Modification to the Classical Method of Calculating Alkalinity in Natural Waters. Journal AWWA.P 56.
- Larson, T. E., Henley, L. 1955. Determination of Low Alkalinity or Acidity in Water. Anal. Chem. 27:851.
- American Society for Testing and Materials. Manual of Water. 1969. 3rd Edition.P 210.