Because the pH scale is logarithmic, a solution of pH 9 is how much more alkaline than a solution of pH 7?

Because the pH scale is logarithmic, each whole-number change represents a tenfold change. So a pH of 8 is 10 times more alkaline than pH 7, and a pH of 9 is 100 times (10 × 10) more alkaline than pH 7. This is why even a seemingly small pH number difference can mean a large chemical difference in how a product affects hair and skin. Understanding the logarithmic nature of the pH scale is emphasized in the scientific-concepts portion of the exam.