What does acidity measure in a solution?

Acidity in a solution specifically refers to the concentration of hydrogen ions (H⁺) and therefore measures the strength or amount of acids present in that solution. When acids dissociate in water, they release hydrogen ions, which is the fundamental basis for acidity. The more hydrogen ions present, the lower the pH and the higher the acidity of the solution.

This concept is crucial in various applications, such as in environmental science where the acidity of water bodies can significantly affect aquatic life, and in chemical reactions, where the acidity may influence the reaction rates and equilibria.

While other aspects such as hydroxide ions, metallic cations, or total dissolved solids involve essential components of water chemistry, they do not directly correlate with the definition and measurement of acidity itself. Thus, focusing on the measure of acids in solution accurately encapsulates what acidity quantifies.