Why might a buffer be needed for aspirin?
Aspirin is also called acetylsalicylic acid and is a derivative of salicylic acid and decomposes to form salicylic acid and acetic acid. The pH of the stomach is 2 = very strongly (hydrochloric acid) acidic. Adding more acid only increases the side effect of gastrointestinal problems such as ulcers. Using a buffer (something alkaline or basic such as bicarbonate) will increase the pH so the stomach is not so acidic.