pH measurement. Electrical pH measurement of an alkaline solution of washing soda (sodium carbonate, NaCO3, right). The pH of a solution is a measure of its acidity or alkalinity. The scale runs from 0-14, water is neutral at pH 7. A pH below 7 is an acid, pH 1 being the most acidic. Alkalis have a pH higher than 7, pH 14 being the most alkaline. The pH of this solution is 10.19.