Calculate the pH of a buffer using dihydrogen phosphate and it's conjugate base. The concentration of weak acid is 0.23 M and the conjugate base concentration is 1.19 M

Use the Henderson-Hasselbalch equation.

To calculate the pH of a buffer solution, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log ([conjugate base] / [weak acid])

In this case, the weak acid is dihydrogen phosphate (H2PO4-) and its conjugate base is hydrogen phosphate (HPO42-). The pKa value for this acid-base pair can be found in a reference table, or it can be calculated using the Ka value.

Now, let's find the pKa value. The Ka for H2PO4- -> HPO42- can be obtained from a reference table or calculated using the following equation:

Ka = [HPO42-] * [H+] / [H2PO4-]

Since we know the concentrations of H2PO4- and HPO42- (0.23 M and 1.19 M, respectively), we can plug these values into the equation along with the concentration of H+ (which is equal to the concentration of HPO42- in this case). Assuming the concentration of H+ is x, the equation becomes:

Ka = (1.19 * x) / 0.23

Now, let's solve for x (concentration of H+) by rearranging the equation:

x = (Ka * 0.23) / 1.19

Once you have determined the value of x, you can substitute it into the Henderson-Hasselbalch equation along with the concentration of the conjugate base (1.19 M) and the weak acid (0.23 M):

pH = pKa + log (1.19 / 0.23)

Calculate the natural logarithm (log) of the concentration ratio (1.19 / 0.23), then add the pKa value to get the pH.

Note: The pKa value for dihydrogen phosphate (H2PO4-) and hydrogen phosphate (HPO42-) is approximately 7.21. Therefore, you can substitute this value and proceed with the calculations.