Dissolving Tylenol Science Experiment - why is it fastest in distilled water? My son has a science experiment for class to dissolve Tylenol (325mg acetaminophen) in 3 different solutions (125 mL volume each):


Distilled water
Vinegar (1 part white vinegar to 4 parts water)
Salt water (1 tablespoon sea salt)


All solutions were at room temperature.  As far as I could tell, the pill had no fillers and there was no coating on them.  On the bottle, the pills are described as 325mg acetaminophen, and there is no mention of non-medical / filler ingredients.

We used pH test strips, and it seemed the vinegar solutions was a pH of about 6, the water 7 as expected, and the salt water 8 or 9. Edit: it may be the pH was 7 for the salt water, see comment below.

His hypothesis was the Vinegar solution, being acidic would dissolve the fastest.  However, the Tylenol dissolved fastest in the distilled water.  The salt water was slowest, and the vinegar solutions was second.

We also tried pure vinegar, and this dissolved even more slowly than the diluted vinegar used at first.

I should add - it didn't really dissolve in any of the solutions, the pill just came apart into small particles.  Even stirring the solutions afterwards didn't seem to dissolve completely.

I am trying to help my son to determine why distilled water broke up the pill the fastest, but I'm afraid I don't know enough to help.

Any pointers, or websites, where I can help him to research greatly appreciated.
Water can only dissolve a certain amount of solids at a given temperature before it reaches saturation. Distilled water has been boiled and captured in gas phase, almost completely eliminating the presence of dissolved solids.  This lack increases the number of ' water to solid' molecular interactions that will take place and so speeds up the disolving.  The same would be true of any solute.