To determine the Alkalinity of given sample of water

To determine the Alkalinity of given sample of water

DISCUSSION:

Alkalinity is the name given to the quantitative capacity of an aqueous solution to neutralize an acid. Measuring alkalinity is important in determining a stream’s ability to neutralize acidic pollution from rainfall or wastewater. It is one of the best measures of the sensitivity of the stream to acid inputs.

Alkalinity is the quantitative capacity aqueous media to react with hydrogen ions. The alkalinity of natural or treated waters is normally due to the presence of bicarbonate, carbonate and hydroxide compound of calcium, magnesium, sodium and potassium. Borates and phosphates and silicates also contribute to alkalinity. Borates and phosphates and silicates also contribute to alkalinity.

PRINCIPLE:

Alkalinity is directly determined by titration with 0.02n H2SO4 using phenolphthalein and methyl orange indicators.

Ca (OH) + H2SO4 → CaSO4 + 2H20

2CaCO3 + H2S01 → Ca (HCO3)2 + CaSO4

Ca (HCO3)2 + H2SO4 → CaSO4 + 2CO2 + 2H20

REAGENTS:

1. Sodium Carbonate Solution 1N: Weigh accurately 13.25g anhydrous sodium carbonate, Na2CO3 Previously dried at 1400C. Dissolve it in little distilled water and make up to 250ml. in a volumetric flask.
   
2. Sulphuric acid 0.02N: Dilute appropriate volume of IN.H2SO4 (about 20m) to 1000ml. in a volume flask with Distilled water, to give a solution of 0.02N Solution
   
3. Phenolphthalein indicator Solution: Dissolve 500mg phenolphthalein in 50 ml. ethyl or isopropyl alcohol and add some, distilled water. Add 0.02N Sodium hydroxide solution drop wise until a faint pink color appears.
   
4. Mixed indicator Solution: Dissolve 20mg methyl rod und 100mg bromocresol green 100ml 95% ethyl or isopropyl alcohol (If the sodium salts of indicator are used, prepare the solution with distilled water instead of alcohol).
   

PROCEDURE:

Phenolphthalein Alkalinity:

1. Place 25ml. or 50ml. or appropriate volume of the sample in 250 ml of conical flask.
   
2. Adjust the volume to 50 ml with distilled water.
   
3. Add phenolphthalein indicator solution.
   
4. If a pink color appears then titrate with 0.02N Sulphuric acid (pH8.3) until the solution becomes colorless.
   

Total Alkalinity:

Add 3 drops of mixed indicator solution to the solution in which phenolphthalein alkalinity

has been determined and titrate against 0.02N Sulphuric acid (to pH 4.6) to light pink.

Wastewaters and Colored Samples:

Conduct the phenolphthalein alkalinity and total alkalinity titrations potentiometrically to the required pH. Any pH-I meter with a glass electrode and calomel electrode is sufficient for this purpose. Sample with alkalinity less than 10mg/l can better be determined by potentiometric titrations.

If the sample contains suspended matter, remove by filtration or centrifugation and then determine the alkalinity. If suspended matter contains any alkalinity, add known excess of standard acid to the sample, boil off carbon dioxide, cool and back-titrate with standard alkali.

Calculations:

If the Sulphuric acid used for the titration is exactly0.02N,

OBSERVATIONS: