For H₃PO₄, a tripotic acid, K_a1 = 7.1 × 10^-3, K_a2 = 6.3 × 10^-8, and K_a3 = 4.5 × 10^-13. What is the pH of a solution that contains 0.300 moles of Na₂HPO₄ and 0.400 moles of KH₂PO₄ per liter of solution?Hint: Treat this as a buffer and use the K_a that matches the given solutions.

Question

Quizplus · Accepted Answer

The correct answer is A because the solution contains Na₂HPO₄ and KH₂PO₄, which form a buffer with K_a = K_a2 = 6.3 × 10^-8. The pH of the buffer can be calculated using the Henderson-Hasselbalch equation:pH = pK_a + log([A^-]/[HA])where [A^-] is the concentration of the conjugate base (HPO₄^2-) and [HA] is the concentration of the acid (H₂PO₄^-).In this case, [A^-] = [Na₂HPO₄] = 0.300 M and [HA] = [KH₂PO₄] = 0.400 M. Substituting these values into the equation, we get:pH = -log(6.3 × 10^-8) + log(0.300/0.400) = 7.08

For H3PO4, a Tripotic Acid, Ka1 = 7

For H₃PO₄, a Tripotic Acid, K_a1 = 7