ACIDITY(FREE MINERAL) TITRIMETRIC METHOD (0-200 PPM) Theory of Test, Apparatus Required, Chemical Required, Procedure for test, Calculation of Results, Limitations of Test Acidity (Free Mineral) Free mineral acidity (FMA) is present in a sample whenever its pH is less than 4.3.  Although it is unusual to encounter a raw water containing free acidity when acidity is present, it is very significant since acids contribute to corrosiveness and influence certain chemical and biological processes.  Note ::: Free acidity is due to the presence of acids such as sulfuric, nitric and hydrochloric and does not include carbonic acid formed by the combination of carbon dioxide and water.  The effluent from a hydrogen zeolite exchange unit will also contain free acid in proportion to the cations present in the raw water.  Determination of the free acidity content of the hydrogen zeolite effluent controls the operating run of these units as well as indicates when regeneration is required.  Acidity (Free Mineral) Titrimetric Method (0-200 ppm) Principle of Test To determine free mineral acidity, the sample is titrated with a standard solution of sodium carbonate to a methyl orange end point (approximately pH 4.3). [Total acidity may be determined by titrant with the same titration to a phenolphthalein end point. (pH 8.3)].