Product Notes
- 7812225 reads
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.
Alkalinity Titrimetric Method (0-200 ppm)
Principle Theory
This test is based on the determination of alkalinity by titration with standard acid to the phenolphthalein color change (or to a pH of 8.3) and to the methyl orange color change (or a pH of 4.3). For determination of hydroxide alkalinity only, barium chloride is added prior to titration to precipitate the carbonate ions. Titration is then taken only to the phenolphthalein end point. A pH meter may be used instead of the indicators to determine the end points of the titration.
Apparatus Required
Buret 25 ml - 1
Porcelain Cup, 210 ml - 1
Glass stirring rod - 1
Graduate, 50 ml - 1
Pipet, delivery, 5 ml - 1
(1 pH meter- optional)
Chemicals Required
Barium Chloride, 10%
Hydrochloric Acid, 0.02N
Methyl Orange Indicator
Methyl Purple Indicator
Phenolphthalein Indicator
Sulfuric Acid, 0.02N.
QUICK HANDY ON SITE TEST can be obtaine through our EASY to USE METHOD ::: RXSOL-62-5515-001
Limitations of Test
Phenolphthalein (P) and Methyl Orange (M) Alkalinity
The alkalinity measured from the titration to phenolphthalein end point or P alkalinity is considered to be equivalent to the sum of all the hydroxide ion present plus one half of the carbonate ion present. The total alkalinity by titration to the methyl orange endpoint or M alkalinity includes the other half of the carbonate ion plus any bicarbonate that was originally present. The presence of phosphate, silica, organic or other buffers may affect the titration and the calculation of the form of alkalinity present may be in error.
The presence of bases other than hydroxide, carbon and bicarbonate will interfere directly.
Common bases titratable by acids include sulfide (S= ) , hydrosulfide ( HS- ), cyanide ( CN-) and ammonia (NH3) . All these will add to the apparent concentration of one or more of the alkalinities .
measured. Care should be exercised in interpreting alkalinities found in these water strictly in terms of scaling tendency. However, under normal circumstances in plant control, expression of result only as the P and M alkalinity actually determined is satisfactory and is preferred from the standpoint of simplicity.
Hydroxide Alkalinity
The method for hydroxide alkalinity is considered accurate only to within 10 per cent. High silica, organic matter and aluminates can interfere with the determination, as will the bases mentioned above. High sulfate content in the sample can produce turbidity which may mask the endpoint. However, the method for hydroxide alkalinity is satisfactory for routine control and can be valuable in the control of lime-soda softening.
