Assertion: The `pK_(a)` of a weak acid becomes equal to pH of the solution at the midpoint of its titration.
Reason : The molar concentrations of proton acceptor and proton donor become equal at the midpoint of titration of a weak acid.

Options

A. If both (A) and (R) are correct and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct, but(R) is not the correct explanation of (A)
C. If(A) is correct, but (R) is incorrect
D. If both (A) and (R) are incorrect

Answer

A

Explanation

According to Henderson-Hasselbalch equation `pH = pK _(a ) + log ""(["proton 9acceptor"])/(["pron donor"])`
Atmidpoint of titration of weak acid `[HA]=[A^(-)]` and hence `pH = pK _(a) + log 1. - = pKa`