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Total hardness include Temporary Hardness and Permanent Hardness
Determination of Temporary Hardness
Temporary hardness of water is caused by the presence of bicarbonates of calcium or magnesium. Hence its amount is estimated by directly titrating with a standard solution of an acid.
Exactly 100 ml of the given sample of water is buretted out or pipetted out into clean conical flask. Two drops of methyl orange indicator are added to it and titrated against HCI acid from the burette. When the water turns to a pale pink colour, the addition is stopped and the reading is noted down. Another titration is conducted for concordancy.
Determination of Permanent Hardness
When a measured excess of standard sodium carbonate solution is mixed with a known volume of hard water, the calcium and magnesium salts are completely precipitated as their insoluble carbonates. After filtration, the unreacted sodium carbonate is determined by titrating against standard HCI using methyl orange as the indicator. From the volume of hydrochloric acid equivalent in alkali carbonate, the amount of hardness is calculated.
A 100 ml of the given sample of water is accurately measured out into a clean conical flask. It is boiled for half an hour. This removes the temporary hardness. To this water, a 10 ml of 0.1N Na2CO3 solution is added and boiled for an hour. The solution is cooled and a freshly prepared distilled water is added to make up the volume loss by evaporation. It is filtered through a filter paper and the filtrate is collected in a conical flask. Two drops of methyl orange indicator are added to the filtrate and titrated against the standard HCI taken in the burette, until the solution becomes of pale pink colour. A duplicate experiment is conducted. From the volume of HCI consumed, the permanent hardness of water is calculated.
(i) Temporary hardness of the given sample of water = ... degrees.
(i) Permanent hardness of the given sample of water = ... degrees. Calculation