A buffer [local] is a mixture of an acid with its conjugate base. Occasionally a salt such as NH₄C₂H₃O₂ acts as a buffer; the ammonium cation is a weak acid, and the acetate anion is a weak base. The resulting solution resists a change in pH.

Some buffer problems may require equilibrium expressions without approximations. The quadratic equation can be utilized effectively with the solver function.

The tutorial entitled Buffers-Composition is about the relative amounts of acid and salt in a buffer. The tutorial entitled Buffers-Properties is about determining the pH of a known buffer after adding an acid or a base. You have to supply the K_a table. Values in K_a tables often do not match.

Questions that will allow you to determine the composition of a buffer.