Question

How to prepare a buffer solution?

We will be assigned a pH. We need to write a procedure in order to prepare 100 mL of a buffer solution of that pH from two solids. The procedure should clearly identify which glassware and chemicals used to prepare the solution. Assume you will use the sodium salt of the conjugate base to prepare the solution.

Answer 1

Suppose we prepare 100 mL of acid buffer solution of a given pH.

We will use weak acid HA and the sodium salt of the conjugate base NaA.

For weak acid HA, the value of pKa can be obtained from google search or it will be given.

Then we will use the following formula

From pH and pKa values, we will calculate the ratio

The required total concentration of weak acid will be given if not, then we will assume it to be 1.0 M. From this concentration and the ratio , we will calculate the number of moles of HA and NaA required. From the number of moles and molar masses, we will calculate the mass of HA and NaA required.

Procedure:

Using weighing paper and weighing balance, weigh the desired mass of HA and NaA. To a 100 mL volumetric flask, add some distilled water. Then add weighed amount of HA. Mix well. Then slowly add weighed amount of NaA and mix well. Then dilute the resulting solution to 100 ml mark with butter paper.