Re: indigestion

Before you get started, I'd recommend that you do some 'research' into the following areas:

1. Acid-Base Chemistry
2. Esophageal Reflux, Acid Peptic Disease and Peptic Ulcers - these are conditions that involve the exposure of epithelial surfaces in the gut to acid secreted from the stomach. If you'd like to take things further, look up Zollinger-Ellision Syndrome, a genetic disease where people secrete too much acid in their stomach.
3. The role of bicarbonate ion in neutralization of acid - the body uses bicarbonate ion (HCO3) to neutralize stomach acid. Specifically, Brunner's glands in the duodenum (the first part of the small intestine) secrete it.
4. Anatomy and physiology of the gut - you should have some idea of how digestion works and what different parts of the gut (stomach, small intestine, large intestine) contribute to the process.

The stomach uses hydrochloric acid (HCl) to assist in digestion. Parietal cells in the stomach wall generate the acid and secrete it into the stomach. 'Indigestion' can represent a variety of problems from too much acid being secreted, defects in the barrier of mucus that lines the stomach to protect it from the acid, to having acid 'splash' back into the esophagus - the tube connecting your mouth with your stomach. The latter case known as 'esophageal reflux' commonly causes what we refer to as 'heartburn' as the esophagus does not have any protection against acid like the stomach does. Acid that hits the lining of the the esophagus burns the tissue, causing the pain.

The pH of fluid in the stomach is around 1-2. pH = negative log of the concentration of hydrogen ions in solution, or 2 = -log[H+]. If you've never had any chemistry you should definitely talk to your science teacher about what this notation means as it will be very important in how you set up your experiments. A pH of 2 correlates with an HCl concentration of .01 Molar in solution. You can make this type of solution using concentrated HCl - BE CERTAIN TO WORK WITH CONCENTRATED ACIDS IN A FUME HOOD AND UNDER ADULT SUPERVISION. WEAR GLOVES, PROTECTIVE CLOTHING INCLUDING EYEWARE, AND BE CERTAIN TO PROPERLY DISPOSE OF ALL ACIDIC MATERIAL.

You could theoretically mimic the situation in the stomach by making a .01M solution of HCl in water - keep in mind that true stomach contents have other components including various ions (sodium, potassium..) and proteins. I'll leave it to your research to identify ways of more closely approximating stomach fluids.

Then try adding different antacids to defined volumes of 'acid' you have mixed. You can purchase strips of pH paper to assist in determining how much acid has been neutralized. The paper will turn a specific color depending on the pH of the soluion. Try over the counter medicines - how much does it take? You could also mix varying solutions of bicarbonate (baking soda) to see how the body's natural antacids compare with mad-made ones.

Good luck..

-P.R.