Final answer:
The pH of the buffer is less than 4.90 because there is a higher concentration of acid than conjugate base. Using the Henderson-Hasselbalch equation, the pH is calculated to be 4.52.
Step-by-step explanation:
The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation, which is:
pH = pKa + log([A−]/[HA])
Where [A−] is the concentration of the conjugate base and [HA] is the concentration of the acid. Given that the pKa of the acid is 4.90, the concentration of the acid (HA) is 9.00 mol, and the concentration of the conjugate base (A−) is 3.75 mol, you can substitute these values into the equation:
pH = 4.90 + log(3.75/9.00)
Calculating the log ratio:
pH = 4.90 + log(0.4167)
pH = 4.90 − 0.3802
pH = 4.52
This result indicates that pH < 4.90. The pH is less than the pKa because there is more acid (HA) than conjugate base (A−) in the buffer.