What type of substance increases the concentration of hydrogen ions when dissolved in water?

An acid is defined as a substance that, when dissolved in water, increases the concentration of hydrogen ions (H⁺) in the solution. This is a fundamental characteristic of acids, which release protons (or hydrogen ions) into the solution, leading to a decrease in pH. For example, when hydrochloric acid (HCl) is dissolved in water, it dissociates completely to release H⁺ ions, thereby increasing their concentration.

In contrast, a base would decrease the concentration of hydrogen ions by either accepting protons or releasing hydroxide ions (OH⁻), which can combine with H⁺ to form water. A neutral substance, such as pure water, maintains a stable concentration of hydrogen ions and hydroxide ions, resulting in a neutral pH of 7. Buffers are solutions that can resist changes in pH when small amounts of acid or base are added, but they do not inherently increase the concentration of hydrogen ions upon dissolving. These distinctions are crucial in understanding the behavior of substances in an aqueous environment and their impact on pH levels.