The scale ranges from 0 to 14, where a pH of 7 is considered neutral. Solutions with a pH below 7 are considered acidic, with a lower pH indicating higher acidity. Solutions with a pH above 7 are considered basic (alkaline), with a higher pH indicating higher alkalinity. The pH scale is logarithmic, meaning that a difference of one unit represents a tenfold difference in the concentration of hydrogen ions (H+) in the solution.