Find the pH of a buffer solution with equimolar concentrations of: HCOOH and NaCOOH (Ka = 3.5 x 10-4 for HCOOH)a
To find the pH of a buffer solution with equimolar concentrations of HCOOH and NaCOOH, we need to consider the dissociation of the weak acid, HCOOH, and its conjugate base, HCOO-. With the given value of Ka = 3.5 x 10^(-4), we can assume that the dissociation of HCOOH is minimal, and most of it remains in the acid form.
To calculate the pH of the buffer solution, we need to use the Henderson-Hasselbalch equation, which is given by:
pH = pKa + log([A-]/[HA])
Where:
- pH is the solution's acidity or alkalinity.
- pKa is the negative logarithm of the acid dissociation constant (Ka).
- [A-] is the concentration of the conjugate base (HCOO-).
- [HA] is the concentration of the weak acid (HCOOH).
Since we have equimolar concentrations of HCOOH and NaCOOH, we can take their concentrations as equal. Let's assume the concentration of each is "x".
Now, let's substitute the values into the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
= pKa + log(x / x)
= pKa + log(1)
= pKa
Therefore, in our case, the pH of the buffer solution is equal to the pKa value of HCOOH, which is 3.5 x 10^(-4).