Question

Aspirin is a weak acid with a pka of 3.5 that is absorbed more effectively in the stomach than the small intestine. The ph of your stomach is around 1.5 and the ph of your small intestine is approximately 6.0. Is aspirin absorbed more readily when it is protonated or deprotonated? What is the approximate ratio of conjugate base to acid when it is absorbed more readily?

Answer 1

`([A^-])/([HA])     = (1)/(100)`

Step-by-step explanation:

The H+ ions separate from the aspirin at pH higher than pKa and then become deprotanated-ve charge. In the protonated form, aspirin is more easily absorbed as it is neutral at pH 1.5 and can easily pass through the lipid bilayer. The absorption in the stomach is very big.

`pH = pKa + log ([A-])/([HA])`

`log ([A-])/([HA]) = pH - pKa`

`log ([A-])/([HA]) = 1.5 - 3.5`

`([A-])/([HA])     = 10^(-2)`

`([A^-])/([HA])     = (1)/(100)`