How does the surface area to volume ratio of a pill affect its dissolution time?

[devinfraser]

Hey guys! I decided to do my science fair project on how the surface area to volume ratio of a pill (I'm thinking a vitamin C pill) affects its dissolution time. I'm planning on using four containers of simulated stomach acid (I already have figured out how to make this) and in the first one I'll have the whole pill, the second one will have the pill split in two halves, the third will have the pill split into quarters and the fourth will have it completely ground up. I will measure the dissolution time one at a time, while stirring, and compare them and see how this relates to the surface area and volume ratio. Does this sound like a good idea to you guys?

A few things I'm not sure about:
-how can I find the surface area measurements for each stage of the pill (especially the ground up one)
-should I only do this process for 1 type of pill, or should I use multiple to show that it's the same process for multiple types of medication

Any suggestions/comments are greatly appreciated!

[17eugenekim]

That certainly sounds like an experimental design!

In terms of measuring the surface area directly, you'll probably have to make some measurements on the pill itself. Is this a disk-shaped pill that you're cutting up? That's a cylindrical sector, and you can find the geometric formula (as well as calculators) online if you look for them. If it's an oblong tablet-like shape, it might be more difficult - perhaps making an approximation as a cylinder and continuing as cylinders of different lengths. If it's an oval, you could approximate it as a rhombus - half a rhombus is a triangle, and a quarter of a rhombus is either another triangle or a trapezoid.

I know that was a lot of visualizing, so it might help to draw it out first, perhaps starting with 2D. Feel free to ask follow-ups as they come.

In science, doing multiple trials is almost always a good idea, especially if you're starting with a small number. If you have more than one, you can do some more statistics and make more advanced graphs, if you wish. As such, multiple trials of the same pill is certainly good; multiple trials of different pills might also be good, but you'll need to provide a justification - for instance, how is the pill different in terms of composition? Do differently made pills dissolve differently?

Hope that helps.

[devinfraser]

Thank you for the advice. I think I'll stick to one pill (probably cylindrical because it's easier to measure that way) and do multiple trials and find the average. I asked my teacher about finding the surface area for the ground up pill and he said it would be okay if I just said it was GREATER THAN whatever the surface area value is for the pill split into quarters.

[17eugenekim]

Sorry I forgot to address the part about the ground-up pill! Yeah, in this case, quantifying surface area is going to be difficult if not impossible. If you just say "ground-up" or "powder" in your results/figures, that should be perfectly fine - people will understand what you did.

[devinfraser]

Great, thanks! I'll post any other questions I have on this thread as I continue the project.

[devinfraser]

I'm performing my experiment. I filled 4 ziploc containers with 100 mL of room temperature vinegar and dropped a whole pill in, two halves of a pill in another, four quarters of a pill in another and a ground up pill in another. It's been about an hour and a half and they haven't completely dissolved. Each sample is basically just white powder on the bottom on the container. My question is is there any way for me to make this process move a bit faster? I am able to restart the experiment so any tips on getting the dissolution time shorter? Or maybe I should be measuring something else, like when it settles to the bottom. Thanks in advance.