what is the definition of ph scale
**The pH scale is a measure of the hydrogen ion concentration. It spans from 0 to 14 with the middle point (pH 7) being neutral (neither acidic or basic). Any pH number greater than 7 is considered a base and any pH number less than 7 is considered an acid. 0 is the strongest acid and 14 is the strongest base. Indicators -- An indicator is a special type of compound that changes color as the pH of a solution changes, thus telling us the pH of the solution.