Question
At pKa = pH, which of the following statements is correct?
| A. |
Concentration of drug is 50% ionic and 50% non-ionic
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| B. |
Absorption of drug is 50% ionic and 50% non-ionic
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| C. |
Concentration of drug is 75% ionic and 25% non-ionic
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| D. |
Concentration of drug is 25% ionic and 75% non-ionic
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Show Answer
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Correct Answer » A
Explanation
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|
The relationship between pH and pKa is given by the Henderson–Hasselbalch equation:
-
- pH = pKa + log (ionized / non-ionized)
When pH = pKa,
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- log (ionized / non-ionized) = 0
- Therefore, ionized = non-ionized
Explanation of the Correct Answer
At pH = pKa:
-
- Ratio = 1:1
- 50% ionized (water-soluble form)
- 50% non-ionized (lipid-soluble form)
Hence, the concentration is equally divided
