AP Chemistrymediummcq1 pt
A chemist wants a buffer at pH 5.00 built on an acid with pKa = 4.74. What [A⁻]/[HA] ratio should be prepared?
A.about 1.8 to 1
B.about 0.55 to 1
C.about 2.6 to 1
D.exactly 1 to 1
Explanation
Core Concept
Rearranging Henderson-Hasselbalch gives log([A⁻]/[HA]) = pH - pKa = 5.00 - 4.74 = 0.26. The ratio is then 10^0.26 ≈ 1.8, meaning the conjugate base must outnumber the acid about 1.8 to 1. Ratios near that value hold the pH within hundredths of a unit of the target.
Correct Answer
Aabout 1.8 to 1
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