Chemistry for Engineers Practice Test

pH is the negative logarithm of the hydrogen ion concentration. By definition, pH = -log10[H+], so the scale is logarithmic: a one-unit change corresponds to a tenfold change in [H+]. Lower pH means more acidic (higher [H+]), neutral is about 7, and higher pH means more basic. The relation pH + pOH ≈ 14 at 25°C connects it to the hydroxide ion concentration, since pOH = -log10[OH-]. Acidity and basicity describe how substances behave in donating or accepting protons, but the numeric measure of how acidic a solution is, on a standard scale, is pH.