How Do You Make A Phosphate Buffer?
Because it contains three acidic protons, phosphoric acid has multiple dissociation constants and can be used to create buffers for either of the three corresponding pHs. The three pKa values for phosphoric acid (from the CRC Handbook of Chemistry and Physics) are 2.16, 7.21 and 12.32. Monosodium phosphate and its conjugate base, disodium phosphate are usually used to generate buffers of pH values around 7, for biological applications, as shown here.Difficulty: AverageTime Required: 10 minutesHere’s How: • Decide on the Buffer Properties Before making a buffer you must know what molarity you want it to be, what volume to make and what the desired pH is. Most buffers work best at concentrations between 0.1 M and 10 M. The pH should be within 1 pH unit of the acid/ conjugate base pKa. For simplicity, this sample calculation will be for 1 L of buffer. • Determine the Ratio of Acid to Base Use the Henderson-Hasselbalch equation (below) to determine what ratio of acid to base is required to
