klimt wrote:
I used the following table from Kaplan:
pH-pKa -2 -1 0 1 2
weak base 1 10 50 90 99
weak acid 99 90 50 10 1
I think:
dissociated = ionized
not unionized
so you have to go to the opposite side
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| NE
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PKa-pH= log (protonated/unprotonated). For a 99% protonated log should be 2, so pKa-PH=2 ----- pH= pKa-2= 6.7
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| doc179
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Let me know if I am wrong. They have not mentioned that the drug is basic or acidic. They say the drug's pKa is 8.7 that means this drug is 50% in the dissociated form at pH 8.7( basic ). only an acid can dissociate in a basic pH. That means the drug is an acid. An acid will be 99% in the dissociated form when the difference between pH and its pKa is +2. pH-8.7=2
So pH = 10.7. Then E must be the answer, right?
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| vallia
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pKa is a measure of acidity. The smaller pka the more acidic the drug is.
pKa < 2 means strong acid
pKa between 2-7 weak acid
pKa between 7-10 weak base
pKa >10 strong base
So this one is a weak base, that means at ph- pKa=-2 the drug is 1% nonionized and 99% ionized=disociated. So i go with A
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| romano
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| romano
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But isn't the dissociated state "B + H+". Then you must raise the pH to get the weak base (I agree that it's a weak base) into a more dissociated form.
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| babydoc4usmle
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this is exactly answer E
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