Using the Henderson-Hasselbalch equation, give the ratio of salt to weak acid for a Veronal buffer with apH of 8.6 and apKa of 7.43.

Using the Henderson-Hasselbalch equation, give the ratio of salt to weak acid for a Veronal buffer with apH of 8.6 and apKa of 7.43.

• A. 14.7/1
• B. 1/8.6
• C. 1.17/1
• D. 1/4.3

Answer: (A)

In this buffer calculation, the Henderson-Hasselbalch relation is pH = pKa + log([A-]/[HA]), so the ratio of salt (conjugate base) to weak acid is [A-]/[HA] = 10^(pH − pKa). Here pH is 8.6 and pKa is 7.43, giving a difference of 1.17. Raising 10 to 1.17 yields about 14.8, so the salt-to-weak-acid ratio is approximately 14.8:1. The option that expresses roughly 14.7 to 1 is therefore the correct choice. The other options reflect incorrect uses of the difference or misinterpretations of the exponent (for example, using 1.17 as the ratio, or taking a reciprocal).

In this buffer calculation, the Henderson-Hasselbalch relation is pH = pKa + log([A-]/[HA]), so the ratio of salt (conjugate base) to weak acid is [A-]/[HA] = 10^(pH − pKa). Here pH is 8.6 and pKa is 7.43, giving a difference of 1.17. Raising 10 to 1.17 yields about 14.8, so the salt-to-weak-acid ratio is approximately 14.8:1. The option that expresses roughly 14.7 to 1 is therefore the correct choice. The other options reflect incorrect uses of the difference or misinterpretations of the exponent (for example, using 1.17 as the ratio, or taking a reciprocal).