A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄ .
What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^? is 7.21.

Question

A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄ . What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^? is 7.21.

Quizplus · Accepted Answer

The addition of KOH will react with H2PO4- to form HPO4^2- and water. Since 0.10 mol of KOH is added, the concentration of H2PO4- will decrease by 0.10 mol and the concentration of HPO4^2- will increase by 0.10 mol. This results in 0.65 mol of H2PO4- and 0.85 mol of HPO4^2- in the solution. Using the Henderson-Hasselbalch equation, pH = pKa + log([base]/[acid]) = 7.21 + log(0.85/0.65) = 7.33.

A Buffer Solution Contains 0