Product Dose

Testing Procedure

Phenolphthalein (P) and Methyl Orange (M) Alkalinity.

Measure 50 ml of sample into a graduated cylinder and transfer to the casserole.  Add four or five drops of phenolphthalein indicator.  If P alkalinity is present, the sample will turn red.  Add standard 0.02N sulfuric acid from the buret, drop by drop, until the last trace of red color is removed by a single drop.  Record volume of titrant added as the P alkalinity reading. 

Add four drops of methyl orange indicator (if no red color developed on the addition of the phenolphthalein indicator, proceed directly to this point) Continue adding acid dropwise until a change in color from yellow to salmon pink occurs.  Record the total volume (including titrant added for the P reading) as the M alkalinity.  In some cases where the methyl orange color change may be difficult to detect, methyl purple indicator may be used in place of the methyl orange.  The methyl purple color change is from green to gray to purple, with the endpoint being the first change to a definite purple. 

In place of indicators, a pH meter may be used for the titration.  The P alkalinity reading is taken to be the volume of titrant required to bring the solution to a pH 8.3 while the M reading is taken as the volume required to bring the pH to 4.3.  The pH meter should be calibrated prior to use according to manufacturers instructions.  The buffers used for standardization should be within the 4.3 to 8.3 pH range. 

Hydroxide Alkalinity 

Measure 50 ml of sample into  the  graduated  cylinder and transfer to the casserole.  Using the pipet, add 5 ml of barium chloride and stir vigorously.  Add four to five drops of phenolphthalein indicator and stir.  If the sample does not turn red, hydroxide alkalinity is not present.  If the sample turns red, add 0.02N hydrochloric acid dropwise until the color changes from red to colorless.  Record the volume of titrant delivered.

Results Calculation FORMULA :::   

ppm alkalinity (as CaCO3) =   ml 0.02N sulfuric acid         x     1000  /    ml sample 

(for hydroxide alkalinity substitute ml 0.02N hydrochloric acid for ml 0.02N sulfuric acid) Using a 50 ml sample, the alkalinity becomes ml of acid titrant multiplied by 20. 

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