Calculating acids,absorption and antibiotics?

[piloting]

There's a new antibiotic developed for oral admin

It has a pH=2 (stomach) , pH=6 in the intestine and pKa=2.1

a)Will the drug dissociate in aqueous soln's as a weak or strong acid?

b)Calculate the drug amount dissociated as % ionized and % non-ionized for each body part

c)Will the compound be absorbed by passive diffusion better in the intestines or stomach?

Here are some equations that'll help

pH=pKa+log[A-/HA]

Ka=[H+]*[A-]/[HA]

%[A-] ionized = ([A-]/[HA]+[A-]) * 100

%[HA-] non-ionized = ([HA-]/[HA]+[A-]) * 100

HA[two arrows pointing in opposite directions]A− + H+

pKa=-log10Ka

These questions have been a real stumper for lots of people in my class

[Darby]

Do the environmental pH's (stomach and intestine) have to be factored in? I'm not sure, just asking.

[piloting]

Do the environmental pH's (stomach and intestine) have to be factored in? I'm not sure, just asking.

Yes

[JackBean]

there is nothing like HA-! It's either A- or HA, as you have it in your equation HA = A- + H+

a) look up definitions of weak and strong acids.
b) all you need is pH=pKa+log[A-/HA]
c) which form (HA or A-) will be in stomach and which form will be in intestine? Which of these forms will difuse more easily through the plasma mebrane?