To determine both the temporary and permanent hardness of the given sample of water 

Water is turned out to be hard owing to the presence of calcium or magnesium bicarbonates and chlorides or sulphates of calcium or magnesium. Correspondingly they are known as temporary hardness and permanent hardness of water. Both temporary and permanent hardness of water are expressed as their equivalents of CaCO3 in parts per 1,00,000 parts of water. This is referred to as Degrees of Hardness of water. For example, if a sample of water contains 10 parts of CaCO3 in 1,00,000 parts of water, it is said to possess 10 Degrees of 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
 

Calculation

1. Temporary Hardness

CaCO3 + 2HCl >>>> >>>>>>>>>>>>CaCl2 + H2O + CO2
100 g of CaCO3                                             2,000 ml of 1N HCl
Titration value                                     3.2 ml of 0.1025N HCl
3.2 ml of 0.1025N HCl                 =    3.5 ml of 0.1N HCl
100 parts of the water required       =  3.5 ml of 0.1N HCl