What Is the Connection between Sulfuric Acid and Hydrochloric Acid?

Sulfuric acid and hydrochloric acid are strong acids, both of which are corrosive and dangerous in concentrated form. Sulfuric acid, (H₂SO₄) is a colorless, slightly viscous, oily liquid and is the more dangerous of the two. Hydrochloric acid, (HCl) is a colorless, odorless liquid that more resembles water than the more viscous sulfuric acid and is also known as muriatic acid. The main connection between sulfuric acid and hydrochloric acid, besides similarities in properties, is the fact that hydrochloric acid can be synthesized from sulfuric acid and common table salt.

Both acids are strongly corrosive and have many uses in industry and science. Sulfuric acid is one of the most common industrial chemicals, and in fact, sulfuric acid production is sometimes used as one gauge of a nation's level of industrial development. Millions of tons of sulfuric acid are produced each year worldwide.

Hydrochloric acid is another important industrial chemical and is used in a number of ways. It also occurs naturally in the digestive juices of many animals. Sulfuric acid also occurs naturally when hydrogen sulfide gas is emitted into the atmosphere by volcanic processes. It then mixes with water vapor, forming the acid, albeit in a very weak form.

The two acids share a connection in other ways as well, primarily in certain chemical properties. They both are capable of reacting with and even dissolving a wide range of elements and compounds although certain substances like glass and some metals are immune to one or both of these acids. Acids are compounds that donate a hydrogen ion in chemical reactions, and when mixed with metals, hydrogen gas is formed. As acids, sulfuric acid and hydrochloric acid both have a pH of less than 7 and will react with any base, which is a substance with a pH above 7. Both are soluble in water as well.

The main connection between sulfuric acid and hydrochloric acid is in the process, called the Mannheim process, by which sulfuric acid is used to create hydrochloric acid. In the Mannheim process, pure sulfuric acid is mixed with common table salt (NaCl), producing a reaction that results in sodium sulfate (NaS₂O₄) and hydrogen chloride which is hydrochloric acid in a gaseous form. The gas is cooled and mixed with water, creating hydrochloric acid.