What is the pH of a buffer that consists of 0.20 M NaH₂PO₄and 0.40 M Na₂HPO₄? For NaH₂PO₄,K_a = 6.2 × 10^-8 A) 6.51 B) 6.91 C) 7.51 D) 7.90 E) 8.13

Question

Quizplus · Accepted Answer

To find the pH of the buffer, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

where pKa is the dissociation constant of the weak acid (in this case, H2S), [A-] is the concentration of the conjugate base (in this case, HS-) and [HA] is the concentration of the weak acid (in this case, H2S).

First, we need to find the pKa of H2S using the given Ka value:

Ka = [H+][HS-]/[H2S]

pKa = -log(Ka) = -log([H+][HS-]/[H2S]) = -log(6.2 x 10^-8) = 7.21

Now we can use the Henderson-Hasselbalch equation to find the pH of the buffer:

pH = pKa + log([A-]/[HA])

pH = 7.21 + log(0.20/0.40) = 7.51

Therefore, the answer is C.

What Is the PH of a Buffer That Consists of 0.20