Science Buddies: "Ask an Expert"

Hi! I'm doing my science fair project on the dissolution rates of brand name and generic name pain relievers, and I need some help.

1) I'm using hydrochloric acid to make the stimulated stomach acid. For every liter of stomach acid I wan to make, I should have 5.6 grams of hydrochloric acid, correct? Also, what temperature should I heat it to?

2) Should I use a glass pipette or a magnetic stirrer to stir the stomach acid? I know a magnetic stirrer is usually used, but I don't think I'll be able to get my hands on one for this project.

Thank you so much!! Any help is greatly appreciated!

Famirka

The following pages should be useful in determining your needed amounts of acid:

http://www.ehow.com/about_5081958_molar ... -acid.html
http://en.wikipedia.org/wiki/Hydrochloric_acid
http://en.wikipedia.org/wiki/Molarity

How much you use is going to depend on the molarity of your acid and the molarity you want to assume for stomach acid. The number of grams of HCl is probably a hard thing to measure directly, as it's not normally sold in pure form as far as I know (but I could be wrong about that).

In terms of stirring, I wouldn't recommend a pipette because it could hold on to a significant amount of acid solution. A simple stirring rod should be sufficient. Be careful not to splash, and be careful to add the acid to the water rather than adding the water to the acid. I don't know whether Hydrochloric Acid is one of the ones that can react violently when water is added, but it's just a good lab habit to get into, as some acids will (sulfuric, in particular).

Hi Fammy,

I don't know the answer to 1), but using a glass pipette for 2) should be fine - remember though to rinse it in water each time directly before and after stirring, and protect yourself against the acid should it splash. At a minimum, protect your eyes!
I agree with Ray though that a glass stirrer is the better choice, if you can get your hands on one.

I'm curious to see your results.
Ivo

Fammy wrote:Hi! I'm doing my science fair project on the dissolution rates of brand name and generic name pain relievers, and I need some help.

1) I'm using hydrochloric acid to make the stimulated stomach acid. For every liter of stomach acid I wan to make, I should have 5.6 grams of hydrochloric acid, correct? Also, what temperature should I heat it to?

2) Should I use a glass pipette or a magnetic stirrer to stir the stomach acid? I know a magnetic stirrer is usually used, but I don't think I'll be able to get my hands on one for this project.

Thank you so much!! Any help is greatly appreciated!

Famirka

Hi Fammy,

You've picked an interesting project.

To answer you question 1), here's a link to some information in Wikipedia that Ray missed in his reply: http://en.wikipedia.org/wiki/Gastric_acid. It will tell you a lot about the chemical make-up of stomach (gastric) acid, especially about it's pH. That's what you'll need to measure after you make up your solution to ensure it resembles gastric acid.

Regarding your question about temperature, I think if you heat it to approximately body temperature, 98.6 F, you would get an excellent simulation of what will happen to those pain relievers in a person's stomach. Keep this in mind, chemical reactions work faster the higher the temperature. As a matter of fact, for every 10 degrees C (that's about 18 degrees F) in temperature increase the rate of reaction doubles. So no matter what temperature you select for your experiment, it would be most important to control it in some manner so each pain reliever gets tested at the same temperature - within a couple degrees F.

Both Ray and Ivo gave you excellent recommendations regarding safety. Always wear safety glasses. Always ADD ACID TO WATER - NEVER the other way around, no matter what kid of acid it is, and I would also recommend a rubber lab apron and good rubber gloves. HCl can be pretty aggressive.

Have fun with your project.

Ed Neu
Buffalo, MN