Texas A&M University (TAMU) BIOL111 Introductory Biology I Exam 1 Practice Exam

The pH scale is a measure of the acidity or basicity of a solution, defined primarily based on the concentration of hydrogen ions (H⁺) in that solution. The scale typically ranges from 0 to 14, with 7 considered neutral. A pH lower than 7 indicates an acidic solution, meaning there are more hydrogen ions present, while a pH higher than 7 indicates a basic (or alkaline) solution, where there are fewer hydrogen ions relative to hydroxide ions (OH⁻).

The reason the pH scale is commonly expressed as ranging from 0 to 14 is due to the way water ionizes and the logarithmic nature of the scale: each whole number change on the pH scale represents a tenfold change in acidity or basicity. While extreme conditions can have pH values lower than 0 or higher than 14 (in highly concentrated solutions), in standard conditions and most biological contexts, the scale is considered to have a maximum range of 0 to 14. This makes the correct response a fundamental concept in understanding the behavior of acids and bases in chemistry and biology.