Question:medium
At pKa = pH, which of the following is true for a drug?
At pKa = pH, which of the following is true for a drug?
Show Hint
When pH equals pKa, the log of the ratio is zero, so the split is even.
Updated On: Jun 24, 2026
- Concentration of drug is 50% ionic and 50% non-ionic
- Absorption of drug is 50% ionic and 50% ionic
- Concentration of drug is 75% ionic and 25% non-ionic
- Concentration of drug is 25% ionic and 75% non-ionic
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Drug ionization is governed by the Henderson-Hasselbalch relationship, where pKa is the negative logarithm of the acid dissociation constant.
Step 2: Setting the pH numerically equal to the pKa makes the log term vanish because $\log 1 = 0$, which forces the concentrations of charged and uncharged drug to be identical.
Step 3: Equal concentrations translate directly to a 50:50 split, so half the drug is ionized and half is non-ionized at pKa = pH.
\[\boxed{\text{50\% ionic and 50\% non-ionic}}\]
Step 2: Setting the pH numerically equal to the pKa makes the log term vanish because $\log 1 = 0$, which forces the concentrations of charged and uncharged drug to be identical.
Step 3: Equal concentrations translate directly to a 50:50 split, so half the drug is ionized and half is non-ionized at pKa = pH.
\[\boxed{\text{50\% ionic and 50\% non-ionic}}\]
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