3. Determine the permanent hardness of water if 25 ml (pipette) of Na2CO3 solution [T(Na2CO3/CaO)=0.002523 g/ml] were added to 200 ml (cylinder) of the water being studied, the mixture was boiled and after separating the precipitate of calcium and magnesium carbonates, the excess Na2CO3 was titrated with 18.42 ml of HCl solution (in an additional titration, 23.68 milliliters of hydrochloric acid with the same indicator were used per 17.47 milliliters of sodium carbonate).

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