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Presented By: Dr. Alka Sharma Assistant Professor Deptt. of Chemistry IPS Academy, IES, Indore Alkalinity of water is due to the presence of those types of substances in water which have tendency to increase the concentration of OH- ions either by hydrolysis or by dissociation of water. Factors:1. The presence of salts of weak organic acids which undergo hydrolysis and consume H+ ions of water. As a result concentration of OH- ions increases in water and water becomes alkaline. 2. The presence of HCO3-, HSiO3- and SiO3-2 ions in water which makes the water alkaline because they have tendency to take up H+ ions from water. Hence the concentration of OH- ions increases in water and water becomes alkaline Alkalinity is a measure of ability of water to neutralize the acids .It is classified as 1. Hydroxide Alkalinity (Due to OH- ) 2. Carbonate Alkalinity (Due to CO3-2) 3. Bicarbonate Alkalinity or Temporary hardness (Due to HCO3-) Alkalinity are also expressed in terms of CaCO3 equivalent like hardness. A Known volume of hard water sample is titrated against standard acid using phenolphthalein & methyl orange as indicator. Color Change at end point Phenolphthalein: Pink to colourless Methyl orange: Pale yellow to organish red. Reaction P M P & M represent the volume of cosumed acid by using Phenolphthalein & Methyl orange indicator respectively Conclusions : S. NO. 1 2 3 4 5 Result up to P & M end point P=0 P=M P = 1/2M P ˃ ½M P˂½M OH- CO 32- HCO 3- 0 P or M 0 2P - M 0 0 0 2P or M 2(M-P) 0 M 0 0 0 M-2P Determination of Phenolphthalein Alkalinity: N1V1 = N2V2 V1 = volume of water Sample N1= Normality of water Sample V2= volume of acid consumed with P (A ml) N2= Normality of acid (N/50) N1 = N2V2 /V1 Strength (mg/l) = Nor X E.weight of CaCO3 X 1000 Determination of Methyl Orange Alkalinity or Total Alkalinity: N1V1 = N2V2 V1 = volume of water Sample N1= Normality of water Sample V2= Total volume of acid consumed with Methyl orange (B ml) or (A+B ml) N2= Normality of acid (N/50) N1 = N2V2 /V1 Strength (mg/l) = Nor X E.weight of CaCO3 X 1000 ( in terms of CaCO3 equivalent) The type & amount of alkalinity is determined by comparing the volume of P & M using the above table.