The ph of a solution is defined as the negative logarithm of the concentration of

PH is the negative logarithm of the hydrogen ion concentration (more exactly the activity), or algebraically pH = −log10 [H+] or pH= log101/[H+]. This notation was invented by Sorensen to make very small numbers fit into a more comprehensible range; thus a hydrogen ion concentration of 0.0000007 molar or 10−7M is pH 7.0. In doing so however he introduced an important peculiarity: the pH scale is exponential. Therefore, a solution at pH 6.0 contains ten-times less H+ than at pH 7.0 and a wort at pH 5.2 contains nearly four times as much H+ as a wort at pH 5.8.

Outermost (valence) electrons