How you can prepare a pH 4.5 buffer from CH3COOH-CH3COONa?
To prepare a pH 4.5 buffer from CH3COOH-CH3COONa, you need to calculate the appropriate amounts of acetic acid (CH3COOH) and sodium acetate (CH3COONa) required. The Henderson-Hasselbalch equation is commonly used to determine the pH of a buffer solution and to find the ratio of acid to its conjugate base.
The Henderson-Hasselbalch equation is as follows:
pH = pKa + log ([A-] / [HA])
Where:
pH = desired pH of the buffer
pKa = acid dissociation constant of the weak acid (CH3COOH)
[A-] = concentration of the conjugate base (CH3COO-)
[HA] = concentration of the weak acid (CH3COOH)
Step-by-step instructions to prepare a pH 4.5 buffer from CH3COOH-CH3COONa:
1. Determine the pKa value of acetic acid (CH3COOH) from a reliable source. For acetic acid, the pKa is approximately 4.76.
2. Choose a desired pH for your buffer. In this case, the pH is 4.5.
3. Calculate the ratio of the conjugate base (CH3COO-) to the weak acid (CH3COOH) using the Henderson-Hasselbalch equation.
pH = pKa + log ([A-] / [HA])
Rearrange the equation as:
[A-] / [HA] = 10^(pH - pKa)
Substitute the given values:
[A-] / [HA] = 10^(4.5 - 4.76)
[A-] / [HA] ≈ 10^(-0.26)
[A-] / [HA] ≈ 0.574
This means that the concentration of the conjugate base (CH3COO-) should be approximately 0.574 times the concentration of the weak acid (CH3COOH) in the buffer solution.
4. Choose a suitable concentration for your buffer. Let's assume you want to prepare a 1M buffer solution.
5. Calculate the appropriate concentrations of acetic acid (CH3COOH) and sodium acetate (CH3COONa) based on the ratio found in step 3.
Let C be the concentration of acetic acid (CH3COOH). Then the concentration of sodium acetate (CH3COONa) will be 0.574C.
Since you want to prepare a 1M buffer solution:
C + 0.574C = 1
1.574C = 1
C ≈ 0.635M
Therefore, the concentration of acetic acid (CH3COOH) should be approximately 0.635M, and the concentration of sodium acetate (CH3COONa) should be approximately 0.364M.
6. Prepare the buffer solution by measuring the appropriate masses or volumes of acetic acid (CH3COOH) and sodium acetate (CH3COONa) based on their concentrations calculated in step 5. Dissolve them separately in distilled water, and then combine them to prepare the pH 4.5 buffer solution.
Remember to carefully handle chemicals, wear appropriate safety equipment, and follow laboratory procedures while conducting any experiments.