Aspirin Questions: Seeking Guru Input

[etc]

these questions were given to us to think 'bout for homework. I thought about the answers but I'm thinking i may be a bit wrong for some? i don't know .. if someone has an extra 2 minutes i'd appreciate their guru imput.

a)
stomach acid has a pH of about 1.5. Given the acidity of the stomach acid, would Aspirin dissolved in stomach acid be mostly in its ionized or un-ionized form?

For this I figured that aspirin is a weak acid and therefore doesn't fully ionize, in fact i think it's mostly in its molecular form. so, it must be in it's un-ionized form most, right? what i don't get about this is how they ask you to take into account the stomach's acidity ... ? anyone?


b) Un-ionized aspirin molecules can readily penetrate the stomach lining into a region of less acidity, this is where the stomach irritation associated with aspirin occurs. use le chatalier to explain.

for this i assume that since the pH is higher, then the equilibrium shift of the reaction would shift to the right and more H+ will be made, which is of course acidic, and it makes the new regions acidic, and therefore it irritates.


thanks guys!

 

[FZ+]

what i don't get about this is how they ask you to take into account the stomach's acidity ... ? anyone?

I suspect it is an equilibrium thing. Low pH = big H+ concentration, which would push the equilibrium with regards to the aspirin molecules a certain way...

for this i assume that since the pH is higher, then the equilibrium shift of the reaction would shift to the right and more H+ will be made, which is of course acidic, and it makes the new regions acidic, and therefore it irritates.

Exactamondo!

 

[ravenprp]

a) Your understanding is correct. Aspirin is a weak acid and therefore mostly exists in its molecular form in the stomach acid. The stomach's acidity does not affect the degree of ionization of aspirin.

b) Your explanation using Le Chatelier's principle is correct. The un-ionized aspirin molecules will react with the excess H+ ions in the less acidic region, leading to the production of more H+ ions and increasing the acidity in that region, which can cause irritation.