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pH Levels and Hydrogen and Hydroxide Ions

Hi, since the concentration of H+ ions (hydrogen ions) determines the pH of an acid and the concentration of OH- ions (hydroxide ions) determines the pH of a base. Will a pH 1 solution have any OH- ions present or will it just be excess H+ ions due to all the OH- ions being neutralised by the H+? If so will this be the same case for a pH 14 solution, just excess OH- ions or will still be some H+ ions that haven’t been neutralised by the OH- yet?

Hi Limo,

Short answer: a solution will always have some H+ and some OH-

The pH of a solution is determined by the concentration of hydrogen ions relative to the number of hydroxide ions. If the concentration of each is equal, we have pH7 (neutral). A higher concentration of hydrogen ions than hydroxide ions results in an acid (pH<7). If the concentration of hydroxide ions is greater (more hydroxide ions than hydrogen ions) then we have an alkali (pH>7).

Any solution will have some OH- and H+ ions (although there is more to that you will learn if you study Chemistry in later years). The pH is determined by how many H+ ions your have compared to the number of OH- ions, you can read more about it [here]. (Water and neutral solutions - Acids and bases - National 5 Chemistry Revision - BBC Bitesize). Interestingly, if there are way more hydrogen ions, and very, very, very few hydroxide ions - the pH can even go below 1. Acidic water from mines has been recorded as low as pH -3.6