3. Preparing a Buffer

Many buffers can be purchased in the commercial circuit. To prepare a buffer of a given pH, the procedure goes as follows:

• Choose a weak acid with a pK_a as close as possible to the required pH. This acid can be a salt of a polyprotic acid.
• Choose an appropiate salt of that weak acid. Use a salt in which the positive ion has no influence on pH (Na⁺ , K⁺).
• Determine the [B]/[A]-ratio needed to attain the wanted pH.
• Dissolve the acid and the salt in water.
• The larger both concentrations, the larger the buffer capacity!

Summary

Preparing a Buffer
Choose a weak acid with a pKa as close as possible to the required pH.
Choose an appropiate salt of that weak acid.
Determine the [B]/[A]-ratio needed to attain the wanted pH.