Instructor’s Copy

Lab Worksheet – My Tummy Hurts

Table 1

Acid solution / Base solution
Color of Phenophthalein / Colorless but may appear milky white due to antacid) / Hot pink, but may appear light pink due to antacid.

Table 2 – How much stomach acid will my antacid neutralize? Answers will vary depending upon which antacids are used. A separate data table showing the results for some common brands is included with this activity.

Measurement taken / Antacid 1 / Antacid 2 / Antacid 3
Brand of Antacid Tested
Weight of the Powdered Antacid Table (grams)
Initial Na(OH) Reading (milliliters)
Final Na(OH) Reading (milliliters)
Total Na(OH) Volume Used To Neutralize Remaining Stomach Acid (milliliters)
Milliliters of Stomach Acid Neutralized by the Entire Antacid Tablet
Milliliters of Stomach Acid Neutralized by ONE GRAM of Antacid
Milliliters of Stomach Acid Neutralized by ONE PENNY’s Worth of Antacid

For 1-6, answers will vary due to antacids used.

1. Which antacid that you tested neutralized the greatest amount of acid per table? ______

2. You have 75 ml of HCl in your stomach. How many tablets of your best antacid would you have

to take before the entire 75 ml of acid was neutralized? ______

3. Which antacid that you tested neutralized the greatest amount of acid per gram? ______

4. Which antacid that you tested neutralized the greatest amount of acid per penny? ______

5. Based on the class data, and taking all calculations into consideration, which ONE antacid would

you recommend that your family and friends purchase? ______

6. Based on the class data, and taking all calculations into consideration, which AONE antacid

would you least recommend for your family and friends to purchase? ______

7. You are experiencing an upset stomach and take an antacid that contains Mg(OH)2 to neutralize

your excess stomach acid. A neutralization reaction occurs and your stomach feels much better!

What chemical compounds are now present in your stomach? Please write the correct chemical

formulas for the compounds now found in your stomach.

Mg(OH)2 + HCl MgCl2 + H(OH) or H2O

8. You get ready to test the strength of a new antacid using the titration method. Just before titrating

you realize you are out of Phenolphthalein Indicator Solution. OH NO!!! You find some Phenol

Red Indicator Solution in the cabinet and decide to use it instead. You add the Phenol Red to your

“stomach” flask and begin titrating. How will you know when all the acid has been neutralized?

If students have not worked with Phenol Red, they should just answer that it will change

colors (the purpose of an indicator). If they know Phenol Red, they should know that it

changes from a yellow in acid to a red color when neutralized.

9. List TWO reasons why a buret is a great laboratory tool to use when completing a titration.

A buret allows you to accurately measure the volume of Na(OH) base added to the acid

flask. A buret makes it easy to add Na(OH) base quickly or in very small amounts – a drop

at a time.

10. Write a pH number that would best fit the following situations as they occurred during this

training lab.

A. The “stomach” acid before adding anything to it. Around 1 or 2

B. The “stomach” acid after adding an antacid tablet. Between the answer to A and 7.

C. The Na(OH) you placed in the buret. Around 12-14

D. The “stomach” acid after adding an antacid tablet, phenolphthalein, and titrating with

Na(OH) until the solution turned a pink color. Around 7

E. The antacid tablet if you were to dissolve it in distilled water. Around 10 or 11