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• pH indicators
• Table 1. Some Common Solutions and Their pH
• Table 2. Some Common Indicators, the pH Range in Which They Change Color, and Their Color Changes

The most common method of indicating the acidity of a solution is by stating its pH. The term pH refers to a mathematical system developed by Danish chemist Søren Sørenson (1868–1939) around 1909. Sørenson originally suggested the term pH as an abbreviation for potential (or power) of hydrogen.

Acids and bases were first defined by Swedish chemist Svante Arrhenius (1859–1927). Arrhenius proposed that acids be defined as chemicals that produce positively charged hydrogen ions, H⁺, in water. By comparison, he suggested that bases are compounds that produce negatively charged...