Procedure – the magnesium content in terms of CaCO3 shall be calculated by subtracting the calcium content (in terms of CaCO3) from the total hardness content (in terms of CaCO3)


The alkalinity is determined by titrated against Std acid. The different types of alkalinities are determined by using, separately phenolphthalein and methyl orange as an indicator in two titrations and phenolphthalein after addition of barium chloride in the third titration.


1. Phenolphthalein indicator
2. Std HCL acid – 0.02
3. Barium chloride sol – 10%
4. Methyl orange indicator


a) Take 100ml of the sample contained in a porcelain basin, add 1ml of phenolphthalein indicator and if a pink colouration is obtained, titrate with Std HCl acid, stirring with a glass rod, till the disappearance of pink colour. Preserver the titrated solution. b) Then add 3 drops of methyl orange indicator and continue the titration until the colour changes from yellow to orange. c) Determine the alkalinity to phenolphthalein of another 100ml aliquot of the sample after adding a crystal of sodium sulphate and 10ml of barium chloride solution and stirring well for 2min. Disregard any reappearance of the pink colour.


Alkalinity to phenolphthalein (p) mg/l = 10 V1

Alkalinity to methyl orange (m) mg/l = 10 V2

Alkalinity to phenolphthalein after addition of barium chloride, mg/l= 10V3


V1 = volume in ml of Std acid used in (a)

V2 = volume in ml of Std acid in (b)

V3 = volume in ml of Std acid in (c)