Science Buddies: "Ask an Expert"

I dissolved different forms of pain killers (tablet, soluble tablet, gel capsule, powder capsule and caplet) in stimulated gastric acid (hydrochloric acid, potassium chloride and sodium chloride). It my experiment I left them for 40 minutes and none fully dissolved. They all dissolved into their smallest for but undissolved particles still remained. After leaving them overnight to see if they would dissolve any further they remained the same. Why might this be?

Hello,
I believe you're conducted some form of the classic "stomach in a flask" experiment.
One reason that the pills aren't dissolving might be because the pH is off. You can use a pH testing strip to test the pH of your solution. Generally, the pH of stomach acid is 1.5 to 3.5.
Another reason may be that the temperature of your solution is too low. It should be about 37 degrees Celsius, or approximately 98.6 degrees Fahrenheit.
Finally, your solution might not be accurately attuned to the ratio of elements in an actual stomach. I found a website with instructions for a similar experiment with measurements/ratios you can use: https://sciencing.com/simulated-stomach ... 56282.html

You should expect the capsules with a gel (or some other similar) covering to dissolve slower than those without these coverings, but the whole process shouldn't take more than 40 minutes!

Hope this helps! Feel free to reply with any other concerns!

Saanya