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_acidhttp://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.