Suppose you wanted to make a buffer of exactly ph 7.00 using kh2po4 and na2hpo4. if the final solution was 0.10 m in kh2po4, wha

Question

matrenka

1 month ago

5

Suppose you wanted to make a buffer of exactly ph 7.00 using kh2po4 and na2hpo4. if the final solution was 0.10 m in kh2po4, wha

t concentration of na2hpo4 would you need? (pka for h3po4, h2po−4, and hpo2−4 are 2.14, 6.86, and 12.40, respectively.)

Chemistry

1 answer:

Tems11 [2.7K] · Answer 1 · 2026-04-01T05:34:00+03:00

The answer is - 0.138 M. The buffer pH can be determined using the Henderson equation. Here, $KH_2PO_4$ acts as a weak acid and $Na_2HPO_4$ serves as its corresponding conjugate base. The weak acid has two protons, while the base contains one. The equation can therefore be expressed in terms of protons transferred. Phosphoric acid can donate protons in three stages; the equation we’ve referenced pertains to the second stage, as the acid then has only two protons available and the base only one. Given the concentration of the acid as 0.10 M, we need to calculate the concentration of the base necessary to form a buffer with a pH of exactly 7.0. Substituting the values into the equation leads us to the solution. Cross-multiplying, we find that [base] = 1.38(0.10), yielding [base] = 0.138. Therefore, the concentration of the base needed for the buffer is 0.138 M.