Buffer solutions are composed of an equal concentration (volume) of weak acid and conjugate base. The acid-base mixture is produced by following the Henderson-Hasselbach equation. This equation shows the relationship of pH concentration to an acid-base mixture. The pH concentration is a big factor in measuring the efficiency of buffer solutions.
Biologically related reactions happen at specific parameters such as pH concentration, thus, using an effective buffer solution is essential to prevent any alteration in the specified pH range. By following some relatively simple guidelines you can make buffer solution.
Instructions
Steps in the Preparation of Buffers
1. Determine the pH range required to create the buffer.
For example, a laboratory test needs to take place at pH 4.00. So you have to create a buffer that will remain at pH 4.00 despite the addition of acid or base solutions.
2. Check the table of Weak acids and their conjugate base for the buffer that will perform best on the required pH range. In choosing the buffer to use, the pKa of the buffer should have the nearest value to your required pH.
In the given example, after looking at the table, the best buffer in pH 4.00 is formic acid-formate mixture because its pKa is equal to 3.75 (table of weak acid and conjugate base shown in image 1).
3. Use the Henderson-Hasselbach equation and substitute the pKa of buffer and pH needed.
In my example, pH = 4.00 and pH = 3.75 (the Henderson-Hasselbach equation is shown in image 2).
4. Finding the concentration of the acid/base ratio is a two-step process: (4a) Calculate the difference between pH and pKa.
Applying this to the example, pH = 4.00 and pKa = 3.75 would give 4.00 -- 3.75 = 1.78
(4b). Then calculate the antilogarithm in the Henderson-Hasselbach equation on step 2. Use your calculator to find the antilogarithm value (see sample equation in image 3).
5. Prepare the chemical reagents that correspond to the concentrations of your base/acid ratio. Mix them in an equal amount or ratio depending on the volume you need to use.
In my example, (see image 4) mixing 25 mL of 0.1M of Formic acid and 25 mL of 0.0178M of sodium formate will yield a total of 50 mL buffer solution.
Tags: Henderson-Hasselbach equation, buffer solution, conjugate base, acid base, acid conjugate, acid conjugate base, acid-base mixture