Analysis of Hydrochloric Acid 

 Procedure for Hydrochloric Acid Analysis

Acids and bases are reactive and therefore play an important role in chemical reactions. The standard test methods for the analysis of hydrochloric acid are covered under the ASTM E224 standard method. These test methods provide for the classification of various grades of hydrochloric acid and for the determination of various impurities. Acid strength and impurity levels are important factors in many hydrochloric acid applications.

The following procedures are described in ASTM E224: 

Total Acidity Determination: This test procedure involves determining the total hydrochloric acid with an acidity of 27-37%. A weighted sample of the acid is diluted in water and titrated with a standardized 0.5 meq/mL (N) sodium hydroxide solution, using phenolphthalein as the indicator.

Baumé Gravity Determination: A sample of hydrochloric acid is placed in a hydrometer cylinder and when the temperature is constant, the Baumé gravity is read from the glass hydrometer. The Baumé gravity is used to classify various grades of hydrochloric acid.

Sulfated Ash Content Determination: This test method involves the gravimetric determination of non-volatile matter after sulfuric acid treatment. The lower limit of determination for sulfated ash is 0.001%. A weighted sample of acid, to which sulfuric acid has been added, is evaporated, ignited, and the residue is weighed.

Iron Content Determination: This test method is a calorimetric estimation of iron in hydrochloric acid. The lower limit of determination for iron is 0.0001%. The iron is reduced and determined calorimetrically with 1,10-phenanthroline (ortho-phenanthroline), which forms an orange-red complex with ferrous iron. The intensity of the color is measured in a photometer calibrated against standardized solutions.

Color determination: This test method measures the color of hydrochloric acid. The lower limit of measurement for equivalent color is 0.05 mg iron(III) per 100 ml. An arbitrary color scale is used that is based on the color produced by adding known amounts of ferric iron to the hydrochloric acid.

Total sulfur content determination: This test method involves the determination of total sulfur, excluding certain organic sulfur compounds, in hydrochloric acid. The lower limit of determination for total sulfur in terms of sulfuric acid is 0.0002%. A sample of acid is treated with bromine to oxidize any oxidizable sulfur compounds to sulfate. The sulfate is precipitated and weighed as barium sulfate.

Video 01: Test for hydrochloric acid