Why does aspirin dissolve the fastest in acid? ASAP

[Gill94]

why does aspirin dissolve the fastest in comparison to other pain relievers????

[donnahardy2]

Hi Gil,

I'm hoping you have had some chemistry, because the molecular interaction of the aspirin with water/acid is the best way to explain this. Solutes, such as aspirin, dissolve in acid due to the chemical composition of the binder used in the tablet and the chemical nature of the solute. Aspirin, or acetylsalicylic acid, or 2-hydroxybenzoic acid 2 carboxyphenyl ester, has a benzene ring, (C6H6) which is hydrophobic (water-hating), and this portion of the molecule does not interact with water. However, the molecule also has a hydrophilic (water-loving) carboxyl group (COOH) and a polar acetyl group (CH3O), which will interact with the polar solvent (H2O and HCl) you are using and allow the pill to dissolve.

Here are two websites that contain more information about aspirin, and one that has more information on solubility.

http://chemistry.about.com/od/demonstra ... spirin.htm

http://www.chemistrydaily.com/chemistry/Salicylic_acid

http://www.chem.lsu.edu/lucid/tutorials ... ility.html

I assume that you have conducted an experiment, and found that aspirin dissolved fastest. If you do more research and find the chemical nature of the inactive binder ingredients in the aspirin, and compare the structure of the other analgesics you have tested, I'm sure you will find that the other molecules in the other pills are larger and less hydrophilic compared to the aspirin.

I assume that you kept the temperature and the concentration of acid the same for all of your samples, as changing these parameters would affect results also. This is a very interesting chemistry problem, but if you haven’t had chemistry, or if my explanation doesn’t help you, please let us know. What did you do in your experiment, and what additional information you need?

Donna Hardy