What is the pH of a buffer solution that is prepared by adding 100.0 mL of a 0.25M KH2PO4 to 190.0mL of 0.50M K2HPO4? The pKa for H2PO4- is 6.82.
Please include the answer so I can see if it matches up with mine.
The options for this question are:
a. 6.82 b. 6.24 c.7.10 d. 7.12 e. 7.40

Question

What is the pH of a buffer solution that is prepared by adding 100.0 mL of a 0.25M KH2PO4 to 190.0mL of 0.50M K2HPO4? The pKa for H2PO4- is 6.82.
Please include the answer so I can see if it matches up with mine.
The options for this question are:
a. 6.82     b. 6.24      c.7.10     d. 7.12      e. 7.40

abb0t · Answer

This is a buffer solution, which means you can use the henderson-hasselbalch equation to solve this: $\sf \color{red}{pH = pK_a + log(\frac{[product]}{[reactants]})}$

Does this make sense? The ratio of the concentration of the products over reactants. Keep in mind that you are adding 100.0 mL of monopotassium phosphate, so you need to take that into consideration for concentration, it is no longer 0.25 M