International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

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Which substance is represented by the formula HNO₃?

Nitric acid
Hydrochloric acid
Sulfuric acid
Acetic acid

The correct answer is: Nitric acid

The substance represented by the formula HNO₃ is nitric acid. This strong acid is well-known in both laboratory and industrial settings. It is a colorless liquid that is commonly used in the production of fertilizers, explosives, and in various chemical syntheses. Nitric acid is characterized by its ability to donate protons (H⁺ ions), which is a defining feature of acids according to the Brønsted-Lowry acid-base theory. In contrast, hydrochloric acid, represented by the formula HCl, is a different strong acid primarily used in cleaning and metal processing. Sulfuric acid, with the formula H₂SO₄, is another important industrial acid known for its role in car batteries and as a dehydrating agent. Acetic acid, known for its presence in vinegar, is represented by the formula CH₃COOH and is a weak acid. Understanding these distinctions helps one recognize the unique properties and uses of each acid.