Science Buddies: "Ask an Expert"

I am doing the experiment on Drug Solubility. I was wondering how to simulate the pH of the stomach as it effects the different medicines that I am testing for their rate of dissolution.

Hi Calicogirl,

This sounds like an interesting project. This project you picked does not have a complete set of instructions as you noticed. I found a similar project that does have a full set of instructions. You should be able to use that as a guide.

https://www.sciencebuddies.org/science- ... p080.shtml

Since the pH of the stomach is about 1-2, you can make a set of solutions with different pH. Make sure you have one at pH near 1, and be very careful with those solutions. I recommend to have an adult to help you with these. Then you could try to dissolve the same amount of drug in each of the test solutions to see which pH works the best in dissolving your drug. If you decide to aggitate the samples, be sure to use the same method for the same amount of time on allsamples.

In order to quantify the solubility, you could first perform a a visual inspection, then filter each solution with a different filter paper. You will then have the undissolved drug from each sample on the filter paper (make sure you label these!). Once the filter paper is dried, you can weigh them to find out which has the most drug leftover (and also the lowest solubility). You will need a sensitve scale in order to do this.

Please let me know if you have more questions. If you are unsure of this project, you can select one with a full set of instructions. Either way, I am sure you will have a great project you can learn from! Good luck

Hi Calicogirl,

This is an interesting project. Sunmoonstars has given you some excellent advice. I would like to add some information about preparing the dilute acid. Stomach acid contains hydrochloric acid. If you start with muriatic acid available from a swimming pool store, this will be about 12 M (12 moles HCl per liter). To make one liter of 0.1 M (pH1) HCl:

1 Liter x 0.1 M/L x L/12 M = .0083 L, or 8.3 ml of concentrated HCl per liter plus 992 ml deionized water. Remember to add acid to water; never add water to concentrated acid. Have an adult do this with you and wear safety glasses and protective clothing.


http://en.wikipedia.org/wiki/Gastric_acid


http://chemistry.about.com/od/chemistry ... cwater.htm

You may be able to find 10% HCl, which is 1.2 M and is a little easier to work with. You would use 10 x more acid, or 83 ml 10% HCl plus 917 ml water to make the pH 1 acid.

To make pH 2, you would use one volume of the pH 1 acid and add 9 volumes of distilled water to make a 1:10 dilution.

Stomach acid is often diluted with food and liquids to pH 3, so if you wanted to test a pH 3 sample, you would make another 1:10 dilution of the pH 2 acid.

Stomach acid also contains sodium chloride and potassium chloride, so you can also add 150 mM NaCl:

0.15 M NaCl x 58 g/M = 8.7 grams sodium chloride per liter.

I hope this helps. Let us know if you have any other questions.


Donna Hardy

I am doing the experiment on Drug Solubility. I was wondering how to simulate the pH of the stomach as it effects the different medicines that I am testing for their rate of dissolution. One of the responses I got from asking this question before said to use "muriatic acid" that was available at a pool supply store, however I am unclear what to add to the muriatic acid in order to make a solution similar to what is acting inside a stomach-- what liquids go into this mixture and how much'??

Calicogirl - I've moved your new post back into this "topic." You want to keep all your posts on this project in the same topic so that experts can see what questions have been asked already and what advice and information has been offered.

I am sure Donna or another expert in this forum will help with your followup question about muriatic acid.

Amy
Science Buddies

Hi Calicogirl,

I will try to explain this again more clearly so you can understand. This is interesting chemistry.

To make a solution that is equivalent to stomach acid, you will add water and sodium chloride (table salt) to muriatic acid. Muriatic acid is another name for hydrochloric acid. If HCl (hydrochloric acid) is not available at school, then you should be able to get it at a pool supply store or maybe from a neighbor who has a swimming pool. You should confirm the concentration of HCl in the acid you obtain, as the concentration can vary. But the most common concentration available is 12 M, or 12 moles per liter. A mole is 6.23 x 10 to the 23rd molecules of HCl, and chemists usually use moles per liter to describe concentrations of solutions.

The pH of stomach acid ranges from pH 1 to 3, so this is a good pH range to use for your experiment:
0.1 M HCl = pH 1, 0.01 M HCl = pH 2. .001 M HCl = pH 3

Stomach acid and other body fluids also contain some salt, a mixture of potassium and sodium chloride. The easiest way to add salt to your test solution is to use table salt, or sodium chloride.

So, if you have 12 M HCl and a container of salt, use the following recipe:

For pH 1:

Add about 990 ml of distilled or deionized water to a container.
Add 8.3 ml of 12 M HCl (follow safety precautions described previously).
Add 8.5 grams of sodium chloride
Mix well.

For pH 2:
Add 900 ml of distilled water to a container
Add 7.6 grams of sodium chloride
Add 100 ml of the pH 1 solution

for pH 3:
Add 990 ml of distilled water to a container
Add 10 ml of the pH 1 solution

Let me know if the HCl you obtain is not 12 M. I recommend that you prepare your solutions at school where you will have access to an accurate balance and graduated cylinders to measure the volume accurately.

Please let us know if you have any questions.


Donna Hardy

Just one small addition. Remember to carry out your experiments at 37 degrees Celsius, as this would more accurately simulate the environment in the stomach.

Mike

Can some one provided a little more simple explanation about how to do this project???? I don't really understand what to do