CHEM1312H - pH of Pure Bases

strong bases remember

-most strong bases are ionic compounds (strong electrolytes) containing OH^-

-they are either group I or II metal hydroxides

-dissociate completely in solution

strong bases

-finding the [OH^-] and pH of a strong base solution is similar to calculating the pH and [H₃O⁺] in strong acids

-the only exception are extremely dilute (<10^-6) strong base solutions as the autoionization in pure water produces a OH^- ion concentration of 1.0 × 10^-7M and will have a contribution to the OH^- concentration (no calculations required)

weak bases

-like weak acids, weak bases partially ionize in water (as indicated by the reversible arrows)

-most common weak bases produce OH^- by accepting a proton from water to form OH^-

-weak bases that are neutral substances are nitrogen containing compounds such as NH₃, CH₃CH₂NH₂, C₆H₅N, etc

-conjugate bases of weak acids such as F^-, CH₃COO^-, CO₃^2-, etc. can act as weak bases in water

finding the [OH^-] and the pH of weak base solutions

-very similar to finding the [H₃O^-] and pH of a weak acid

-to find the pH you can use one of two methods:

• using K_w at 25C, 1.0 × 10^-14 and solve for the [H₃O⁺] then pH

• solve for pOH then solve for pH using pH + pOH = 14.00

-provided with number of decimal places to report