The pKa of 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 (A-) to proton donor (HA) in a solution of a weak acid can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). Given a pH of 7.0 and a pKa of 4.0, the equation becomes 7 = 4 + log([A-]/[HA]), which simplifies to log([A-]/[HA]) = 3. This means that [A-]/[HA] = 10^3 = 1000, so the ratio of proton acceptor to proton donor is 1000:1.

The PKa of a Certain Weak Acid Is 4