Where to Turn for Heartburn:

Evaluating the Effectiveness of Antacids

Question: Which antacid is the most effective in neutralizing acid?

Lab Overview: In this investigation, you will compare the effectiveness of two different antacid medications. To do this, you will measure the amount of vinegar (a weak acid) needed to change the pH of solutions containing each antacid from a starting pH of 7 to a final pH of 4.

Background: The lining of your stomach secretes hydrochloric acid (HCl) that aids digestion. This strong acid normally remains in the stomach, which is protected from acid burns by a mucous layer. However, stomach acid can sometimes flow into the esophagus, the tube that connects the mouth to the stomach. If stomach acid comes into contact with the lining of the esophagus, a burning pain in your chest known as heartburn occurs.

Antacid medications 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 the H+ ions and form molecules of water (H2O). Removing the H+ ions makes the solution less acidic (bringing the pH up). Other antacids, such as calcium carbonate (CaCO3) and sodium bicarbonate (NaHCO3), act as buffers when dissolved in water. These buggers regulate pH by removing H+ ions from the solution when their levels increase and donating H+ ions to the solutions when their levels decrease.

Materials:

Antacids (2 types)

Mortar and Pestle

Cups or Beakers (2)

Marking Pens or Labels

Graduated Cylinder

Water

2 Plastic Spoons

Pipette

Universal Indicator Solution

Vinegar (weak acid)

Procedure:

Preparing Antacid Solutions:

  1. Read the dosage information and procure (get) one dosage of each type of antacid.
  2. Label one beaker/cup Antacid A and the other Antacid B.
  3. Crush one dosage with the mortar and pestle and place in Cup A. Keep mortar dry and wipe out carefully with a paper towel. Crush sample B and place in Cup B. Clean and return your mortar and pestle.
  4. Add 100mL of water to each cup. Mix each solution thoroughly with a separate spoon for each cup. Record in your data table the type of antacid is in cup A, repeat with B.
  5. Add 1-2 mL of universal pH indicator to each cup. You should have a definite green color.
  6. Use the color chart to determine the starting pH of each solution. Record the initial/starting pH of each solution in your data table.

Adding Acid to the Antacid Solutions:

  1. Add 0.5 mL of vinegar to each cup and stir with a plastic spoon. Be sure to use a separate spoon for each solution.
  2. Wait until the color has stabilized. Use the color chart to determine the pH and record the pH of each solution in your data table.
  3. Again, add 0.5mL of vinegar to each cup and stir with a plastic spoon.Be sure to use a separate spoon for each solution.
  4. Again, wait until the color has stabilized. Use the color chart to determine the pH and record the pH of each solution in your data table.
  5. Keep a running total of the amount of acid you have added to each cup. Once you have added a TOTAL of 5 mL per cup you may begin adding 1mL per cup, stirring, and checking pH/color.
  6. Continue adding 1mL per cup until each cup reaches a pH of 4. Note: one cup may reach pH 4 before the other. If this is the case, set that cup aside and continue with the second cup until they are both at pH of 4.

You will need the following data tables:

Data Table 1: Total Amount of Acid Added to Each Cup.

Starting pH / After
0.5mL / After 1.0mL / After 1.5mL / After 2.0mL / After 2.5mL / After 3.0mL / After 3.5 mL / After 4.0mL
Antacid A
Antacid B

Data Table 1 Continued:

After 4.5mL / After 5.0mL / After 6.0mL / After 7.0 mL / After 8.0 mL / After 9.0mL / After 10.0 mL / Continue table as needed until pH of 4
Antacid A
Antacid B

Data Table 2: Class Data (Add extra columns if you have more than 9 groups)

Group / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9
mL of Acid added to Antacid A to reach pH of 4
mL of Acid added to Antacid B to reach pH of 4

Analysis & Conclusions:

Create a line graph showing the data you collected for both antacids. (Ask your teacher if you should graph your group’s data, the class data, or both.) The x-axis of your graph should show the independent variable and the y-axis should show the dependent variable. Be sure to include all required parts of a valid graph.

Questions:

  1. What molecule is formed when H+ ions and OH- ions are combined?
  2. Which of the two antacids you tested was more effective at neutralizing the acid? (Think carefully and use your data.) Explain your results using your data.
  3. Of the class overall, which antacid was the most effective?
  4. Whose data is more reliable, your groups or the class data? Why?
  5. Some antacids worked better than others, but all of them eventually lose their effectiveness and allowed the solution to become acidic. What do you think was happening in the antacid solution when the pH started to become acidic?
  6. Suggest a reason why some antacids might be more effective than others.