A patient was brought into the hospital unconscious and was found to have a plasma pH of 7.1. Determine the moles of NaH 2 PO 4 and Na 2 HPO 4 that would be required to prepare 1 liter of a 0.2 M sodium phosphate buffer at pH 6.8. The pKa for H 2 PO 4 is 6.86. Based on the moles of each species determined in the previous question, calculate the ionic strength of this buffer.
Buffers are most effective within one pH unit of the pKa.
A buffer can be prepared by adding hydrochloric acid to the proper amount of a weak base until the desired pH is attained. At a pH below its pKa a buffer may consist of a mixture of a weak acid and a lesser amount of its salt. The phosphate buffer system is the predominant buffer in the blood. Tris is a base that reacts with protons as shown below. Calculate the pH of a buffer that was prepared by dissolving 0.02 moles of NaHCO 3 in slightly less than a liter of water.