Standard Buffer Solutions - Preparing Na Acetate Buffers | Chemistry Net

# Standard Buffer Solutions - Preparing Na Acetate Buffers

Standard Buffer Solutions -Preparing Na Acetate Buffers

# Standard Buffer Solutions -Preparing Na Acetate Buffers

In a previous post entitled "Buffer Solutions - How to prepare buffer solutions" the basic steps for designing buffers were presented. It was shown that it is possible to prepare buffer solutions that maintain the pH close to any desired value by the proper choice of a weak acid and its conjugate base and their relatitive concentrations.

The following steps can be used to prepare standard buffer solutions:

• Determine the optimal pH (the required pH)
• Select a weak acid with a pka near the desired pH
• Calculate the ratio of salt to acid required to produce the desired pH (Henderson-Hasselbach equation): pH = pka - log [HA]O/[A-]O
• Determine the desired buffer capacity of the solution
• Calculate the total buffer concentration required to produce this buffer capacity ß (Van Slyke equation): ß = 2.3* C* (ka * [H3O+]) / (ka + [H3O+] )2
• Determine the pH and the buffer capacity of the final buffer solution using a reliable pH meter.

As an example it was described how to prepare a standard phosphate buffer solution and a phthalate standard buffer solution. In this post it will be shown how to prepare an acetate buffer (pH 4.1 to 5.5).

Acetate buffer

• Prepare the following solutions:

Acidic Acid, 2 N:

1. Add 116 ml of glacial acetic acid to sufficient water to make 1000 ml after cooling at room temperature.
• Place the specified amount of sodium acetate NaC2H3O2 . 3 H2O in a 1000 ml volumetric flask
• Add the specified volume of the 2 N acetic acid solution shown in the table below
• Add water to volume and mix.

Table 1: Acetate buffer - Standard Buffer Solution
pH (pH measured) 4.1 (4.10) NaC2H3O2 . 3H2O 2 N CH3COOH (ml) 1.5 19.5 1.99 17.7 2.99 14.0
 4.7 (4.70) 4.9 (4.90) 3.59 11.8 4.34 9.1 5.08 6.3 5.23 5.8
 5.3 (5.30) 5.4 (5.40) 5.61 4.4 5.76 3.8
 5.5 (5.48) 5.98 3

References

1. CRC Handbook of Chemistry and Physics, 52nd edition, The Chemical Rubber Co., (1971)
2. U.S. Pharmacopeia, 68, USP 36
3. David W. Oxtoby, H.P. Gillis, Alan Campion, “Principles of Modern Chemistry”, Sixth Edition, Thomson Brooks/Cole, 2008
4. Steven S. Zumdahl, “Chemical Principles”  6th Edition, Houghton Mifflin Company, 2009

Key Terms

preparing standard buffer solutions, acetate buffer, buffers, 5 buffer,