An acid is a substance that, when placed in solution, does what to the hydrogen ion concentration?

1. Acids and bases are defined in terms of their opposite effects on hydrogen ion concentration in solution. 2. The text states: "An acid is a substance that increases the concentration of hydrogen ions (H+) in a solution, usually by having one of its hydrogen atoms dissociate." 3. A base does the opposite -- it lowers H+ concentration, whether directly or by supplying hydroxide ions that combine with H+. 4. So by definition, an acid raises the hydrogen ion concentration of a solution. _Source: OpenStax Biology Ch 2 "The Chemical Foundation of Life", p.51 §2.2 | Water_