The pK_aof a certain weak acid is 4.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0. A) 1000:1 B) 20:1 C) 3:1 D) 1:1 E) The ratio cannot be calculated without knowing the structure of the weak acid.

Question

Quizplus · Accepted Answer

The ratio of proton acceptor to proton donor can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). At pH 7.0 and pKa 4.0, the equation becomes 7 = 4 + log([A-]/[HA]), so log([A-]/[HA]) = 3. Therefore, [A-]/[HA] = 10^3 = 1000:1.

The PKa of a Certain Weak Acid Is 4

The PK_aof a Certain Weak Acid Is 4