Acidity In Water

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9. Acidity in Water and Waste Water Introduction:
Acidity of water is its quantitative capacity to react with a strong base to a designated pH. Strong mineral acids such as carbonic acid and acetic acid contributes to acidity of the water while dissolved carbon dioxide (CO2) is the major acidic component of unpolluted surface waters. Acidity (or base-neutralizing capacity) in water and waste water is the measure of acid radicals produced by the dissociation of acid present in the sample. This is determined by titrating an acid wastewater (pH<7) with a strong base. Industrial wastewaters containing high mineral acidity should be properly neutralized before they are subjected to biological treatment or direct discharge due to the following
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If the pH is less than 6.0, it must be boiled for 15 minutes and cooled at room temperature. (c) Sodium hydroxide solution (0.02 N): 1N sodium hydroxide solution is prepared by dissolving 40 g of L.R grade NaOH in distilled water and diluting it to 1000 ml. For the preparation of 0.02 N NaOH solution, take 20 ml of IN NaOH and dilute it to 1000 ml. 0.02 N NaOH can be standardize against standard potassium acid phthalate. 1.0 ml 0.02 N NaOH = 1.0 mg CaCO3
(d) Phenolphthalein indicator: Dissolve 0.5 g of phenolphthalein in 100 ml alcohol and water.
(e) Methyl orange Indicator: Dissolve 0.5 g of methyl orange in distilled water and dilute it to 100 ml in a volumetric flask.


Indicator Method: Pipette 20 ml or a suitable aliquot of sample into a 100 ml beaker. Divide the sample water into two parts and determine the pH of two parts. If pH is less than 3.7, add two drops of methyl orange indicator into the first sample beaker and titrate with standard 0.02 N sodium hydroxide solution until the color changes to the faint orange. Record the volume of sodium hydroxide consumed to neutralize H+ ions. To the second sample beaker, add 2 or 3 drops of phenolphthalein indicator and titrate with 0.02 N sodium hydroxide solution until the color changes to faint pink color. Record the volume of sodium hydroxide used to neutralize

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