Bio IIName:
Evaluating the Effectiveness of Antacids
(Prentice Hall: Where to Turn for Heartburn)
Question: Which antacid is the most effective in neutralizing acid?
Introduction: You will start your investigation of antacid effectiveness by taking a closer look at how acids and bases interact. To begin, you will construct models of hydrogen ions (H+) and hydroxide ions (OH-) to discover what happens with these ions during a neutralization reaction. You will also make models of buffer molecules and explore what happens when an acid is added to a buffer solution. You will also make models of buffer molecules and explore what happens when an acid is added to a buffer.
Background: The parietal cells lining your stomach secrete hydrochloric acid (HCl) to aid in the digestion of food. The strong acid normally remains in the stomach, which is protected from acid burns by a mucous layer secreted by Goblet cells. However, stomach acid can sometimes passthrough the cardioesophageal sphincter into the esophagus. This is known as gastroesophageal reflux disease (GERD) or more commonly known as heartburn.
Antacid mediations are used to treat heartburn and other medical problems caused by stomach acid. In an aqueous solution, HCL breaks apart completely into H+ and Cl- ions. Antacids contain bases, compounds that can remove H+ ions from aqueous solutions. Some bases found in antacids, such as aluminum hydroxide, Al(OH)3, do this by adding OH- ions to the solution. The OH- ions combine with H+ ions and form molecules of water. Removing the H+ makes the solution less acidic. Other antacids, such as calcium carbonate (CaCO3) and sodium bicarbonate (NaHCO3), act as buffers when dissolved in water. These buffers regulate pH by removing H+ ions from the solution when their levels increase and donating H+ ions to the solution when their levels decrease.
Only you and your lab partner will complete the Pre-lab activities.
Pre-lab Activity-Neutralization
Using a paper clip, gummy ring, and a marshmallow, one lab partner needs to build an OH- ion (representing the base) like the one shown below. The other lab partner will have a single marshmallow for the H+ion (representing the acid).
1. If the H+ ions are added to a solution of OH- ions, how will these ions interact?
2. Build the new model and draw it below.
3.a. What molecule was formed?
b. In a neutralization reaction, what else results besides this molecule?
Pre-lab Activity-Interaction Between Acids and Buffers
Construct a model of the buffer molecule like the one shown below. Straighten three paper clips and twist them around each other. Put marshmallows on three of the six ends to represent H atoms. The three free ends represent negatively charged regions.
1. If H+ ions are added to the “buffer solution,” what will happen to the H+ ions? Why?
2. What would happen to the pH of a buffer solution when a small amount of acid is added? Explain!
3. If you keep adding more and more acid to the buffer solution described in question 2, what will happen to the pH over time? Explain!
- Fill in the names of the antacids you tested. Also record the active ingredient (calcium carbonate, sodium bicarbonate, or aluminum hydroxide) and its amount.
Antacid Name / Active Ingredient / Amount
1
2