For strong acids: pH = -log[H+] = -log(C) where C is the molar concentration. For 0.01 M HCl, pH = 2. For strong bases: pOH = -log[OH-], pH = 14 - pOH. For 0.01 M NaOH, pH = 12. The tricky cases: (1) Very dilute acids (C < 10^-6 M): water's autoionisation (10^-7 M H+) becomes significant. For 10^-8 M HCl, total [H+] = 10^-8 + x, where Kw = (10^-8 + x)(x). Solving gives [H+] approximately 1.05 x 10^-7, pH approximately 6.98 (not 8!). An acid can never have pH > 7. (2) For polyprotic strong acids like H2SO4: first dissociation complete, second may be incomplete (Ka2 = 0.012). At low concentrations, the second proton matters.