The pH of sodium acetate/acetic acid buffer is 4.5 . Calculate the ratio of [CH3 COOH]/[CH3COO-]
PLEASE WORK THIS ASSIGNMENT
Use the Henderson-Hasselbalch equation.
homework
To calculate the ratio of [CH3COOH]/[CH3COO-], you need to consider the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the ratio of the acidic and conjugate base components in the buffer. The Henderson-Hasselbalch equation is:
pH = pKa + log([A-]/[HA])
In this equation:
- pH is the given pH of the buffer solution (4.5 in this case).
- pKa represents the dissociation constant of the weak acid, acetic acid (CH3COOH), which you need to know. The pKa value for acetic acid is 4.75.
- [A-] represents the concentration of the conjugate base, acetate ion (CH3COO-).
- [HA] represents the concentration of the weak acid, acetic acid (CH3COOH).
Now, let's rearrange the Henderson-Hasselbalch equation to solve for the ratio of [CH3COOH]/[CH3COO-]:
pH = pKa + log([A-]/[HA])
Substituting the given values:
4.5 = 4.75 + log([A-]/[HA])
Rearranging the equation:
log([A-]/[HA]) = 4.5 - 4.75
log([A-]/[HA]) = -0.25
To get the actual ratio [CH3COOH]/[CH3COO-], we need to convert the logarithmic expression back into a normal ratio. We can do this by taking the antilog (base 10):
[A-]/[HA] = 10^(-0.25)
Using a scientific calculator or any tool capable of calculating exponents, the value of [A-]/[HA] is approximately 0.5623.
Therefore, the ratio of [CH3COOH]/[CH3COO-] in the sodium acetate/acetic acid buffer with a pH of 4.5 is approximately 0.5623.