Jump to main content

Calcium Carbonate to the Rescue! How Antacids Relieve Heartburn

293 reviews


Have you ever experienced heartburn after eating a large, greasy meal? Or have you heard of someone complaining about heartburn pains? It's very common; over 60 million people in the U.S. have heartburn at least once every month. Heartburn pain usually results from stomach acids escaping from the stomach and irritating the esophagus above it. Luckily, there are medical drugs, called antacids, which can help relieve heartburn pain. But how do antacids work, and how effective are they? In this science project, you will create artificial stomach acid and explore how antacids neutralize this super acidic soup!


Areas of Science
Time Required
Short (2-5 days)
Material Availability
Readily available
Low ($20 - $50)
Wear safety goggles and gloves and have an adult help you when handling and working with the artificial stomach acid solution. Hydrochloric acid is corrosive to hands and eyes.

Teisha Rowland, PhD, Science Buddies

  • TUMS® is a registered trademark of the GlaxoSmithKline group of companies.


Determine how antacids change the pH of stomach acid.


When you eat a piece of food, after you chew it in your mouth, it makes its way to your esophagus, a long tube that leads down to your stomach. See Figure 1 below for a diagram of how the esophagus and stomach are connected in the human body. The fluids in your stomach are very acidic, having a pH of around 1 to 3 to help break down your food. pH is a scale that measures how acidic or basic a solution is. A neutral pH is 7, such as distilled water. An acidic pH is below 7, such as lemon juice or battery acid. A basic pH is above 7, such as baking soda or bleach. For a refresher, see the Science Buddies page on Acids, Bases, & the pH Scale.

Simple diagram of the human digestive system with the esophagus, stomach and small intestine labeled
Figure 1. When you eat a piece of food, it travels from your mouth, down through your esophagus, and to your stomach. As the food continues to be digested, it travels through the small intestine. This diagram shows only part of the entire digestive system.

Sometimes, some of a person's stomach acid escapes from the stomach and flows up into part of the esophagus. This is called acid reflux. Eating certain foods or beverages (such as fatty foods or coffee), being overweight, or eating large meals can trigger acid reflux. Because the esophagus is usually at a neutral pH, it is not used to dealing with such an acidic solution. Consequently, during acid reflux the stomach acid irritates the esophagus, causing the common feeling of heartburn. Heartburn is most commonly a pain felt in the chest and usually, but not always, results from acid reflux. A person who frequently experiences extreme heartburn may have gastroesophageal reflux disease (GERD), which can severely damage the esophagus tissue over time.

Luckily, there are medicines, called antacids, which can help relieve heartburn pain. Antacids essentially work by increasing the pH of the very acidic stomach acid. They don't need to raise the stomach acid pH all the way to a neutral pH of 7, but just raising the pH to 3 or 4 will make a person feel better. This is done through an acid/base chemical reaction, which is shown in Equation 1 below.

Equation 1:
Acid + Base → Salt + Water

Equation 1 says that when an acid and a base react together, they produce a salt and water.

Stomach acid mostly contains hydrochloric acid (HCl), a very strong acid. The active ingredient in many antacids is calcium carbonate (CaCO₃), a base that is actually found in several natural minerals, including limestone, marble, and chalk. This acid and base react as shown in Equation 2 below.

Equation 2:
2 HCl (acid) + CaCO₃ (base) → CaCl₂ (a salt) + CO₂ (carbon dioxide, a gas) + H₂O (water)

Equation 2 says that when HCl and CaCO₃ react together, they produce calcium chloride (CaCl₂), carbon dioxide, and water.

What is important about Equation 2 above is that before antacids are added to the stomach, it contains a lot of HCl, but after the antacids are added and react in the stomach, it contains salt, carbon dioxide, and water. The base (the antacid) turns the acid primarily into salt and water.

Although Equation 2 shows that antacids can neutralize stomach acid, just how much antacid is needed to raise the pH of a full stomach, which can hold over two liters, to a pH of 3 or 4? How much antacid is needed to raise it higher than that? In this science project, you will create artificial stomach acid and investigate how antacids neutralize it. Although the stomach is a complex organ, you can create artificial stomach acid that has very similar chemical properties to real stomach acid by using hydrochloric acid and sodium chloride (table salt) to create a solution with a pH of 2.

Terms and Concepts



For help creating graphs, try this website:

  • National Center for Education Statistics. (n.d.). Create a Graph. Retrieved June 2, 2009.

Materials and Equipment

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

Creating Stomach Acid

In this first part of this procedure, you will be creating artificial stomach acid. You will mix together hydrochloric acid (HCL) and sodium chloride in a 2 liter (L) plastic bottle. You will be creating a solution that is 0.01 M hydrochloric acid and 0.150 M sodium chloride, with an overall pH of 2. (0.01 M means it is a 0.01 molar solution, and this represents the amount of a chemical substance that is in a certain amount of liquid.) For more on molar solutions and molarity, read the ChemTalk article on Molarity.

  1. Be sure to wear your safety goggles and latex gloves. Also wear clothes that you would not mind getting damaged. Look at the Science Buddies Chemistry Safety Guide for guidance on how to work with potentially hazardous chemicals. You can also read a webpage on Material Safety Data Sheet on Hydrochloric Acid made by Fisher Scientific.
  2. Cover the surface that you will be working on with newspaper to protect it.
  3. Rinse the 2 L bottle thoroughly with water, but do not use soap.
  4. Using a measuring cup, carefully fill the 2 L bottle with 1.8 L (1800 mL) of distilled water. You may want to use a clean plastic funnel for this step.
  5. To the 2 L bottle, carefully add 200 mL of 0.1 M (also called "0.1 N") hydrochloric acid. You may want to use a clean plastic funnel for this step.
    1. Note: If you are using a concentration higher than 0.1 M for your stock solution of hydrochloric acid, dilute it to 0.1 M HCl using distilled water (making a total of 200 mL) before adding it to the 2 L bottle. Be sure to read and follow the safety instructions for using a more concentrated HCl solution. Read this Science Buddies "Ask an Expert" discussion for information on how to use a different stock concentration of HCl for this experiment:
      1. Science Buddies. (2010, March 21). Science Buddies: "Ask an Expert," Drug Solubility. Retrieved September 16, 2011, from http://www.sciencebuddies.org/science-fair-projects/phpBB3/viewtopic.php?f=25&t=6242
  6. To the 2L bottle, add 17.4 grams of sodium chloride (not iodized).
    1. 17.4 grams of sodium chloride is generally about 3.1 teaspoons. Check the Serving Size on the "Nutrition Facts" of the sodium chloride container to confirm this.
  7. Screw the lid tightly on the 2 L bottle. After making sure it is securely closed, turn the bottle upside down repeatedly until all of its contents appear mixed.
    1. Caution: Hydrochloric acid is dangerous, so be very careful not to get any on your skin, clothing, or especially your eyes. Be sure that the bottle closes securely before turning it upside down to mix its contents. Adult supervision is recommended.
  8. Carefully remove the lid on the 2 L bottle, and measure the pH of the solution using a pH measuring stick. It should be around pH 2.
    1. Copy Table 1 below in your lab notebook and fill it out as you collect your data throughout this Procedure. Write this initial pH in the table in your lab notebook, making note that this is the pH before any TUMS® have been added.
Number of TUMS® pH for Trial 1 pH for Trial 2 pH for Trial 3 Average pH
Table 1. This is a sample table that shows how you can record your data for three different trials, and then calculate the average pH for all three trials.

Neutralizing Stomach Acid with Antacids

In this part of the procedure, you will be adding antacids to the artificial stomach acid you just made to see how antacids affect the pH of the stomach acid.

  1. Have an adult help you use a knife to cut a TUMS tablet into equal-sized quarters. Do this on a piece of paper so that you do not lose any pieces and so that you can easily pour the TUMS into the bottle in the following step.
    1. Crush each quarter tablet into a fine powder by first further breaking up the pieces with a knife and then, crushing these pieces using the back of a metal spoon.
    2. Keep each powdered TUMS quarter separate from the other quarters.
  2. Add ¼ of a powdered TUMS tablet to the 2 L bottle of artificial stomach acid you just made.
  3. Screw the lid of the 2 L bottle on securely, and very carefully turn the bottle upside down repeatedly until the contents appear mostly dissolved.
    1. You may see some little bubbles in the solution. Based on Equation 2 in the Introduction, what do you think these bubbles are?
  4. Measure the pH with the pH measuring stick. Record the total amount of TUMS® tablets added so far and the corresponding pH in the table in your lab notebook.
  5. Repeat steps 2 to 4 until the pH is approximately 4.
    1. Prepare more powdered TUMS quarters as needed by repeating step 1.
    2. Watch the artificial stomach acid solution as you add more TUMS tablets. How does the solution change as you add more TUMS tablets? Write any observations in your lab notebook.
    3. Make sure to record the number of TUMS quarters it took to raise the pH to 4.
  6. Continue to repeat steps 2 to 4 until you have added a total of three more entire TUMS tablets.
    1. For this step, you can add one half of a TUMS tablet at a time. Prepare the powdered TUMS halves you need by repeating step 1, but cut the tablets into halves instead of quarters.
    2. After adding a total of three more TUMS tablets, what was the maximum pH that the solution reached?
  7. In order to ensure that your results are real and accurate, repeat all the steps of the section titled "Creating Stomach Acid" and steps 1 through 6 of this section at least two more times for a total of at least three trials. Remember always to record your data in your lab notebook.
  8. When you are all done, it is safe to dispose of the neutralized stomach acid by pouring it down the sink.

Analyzing Your Results

  1. Calculate the average pH for all of the trials when the same amount of TUMS was added. Write the averages in the table in your lab notebook.
    1. For example, when a total of 1.5 TUMS was added in each trial, if the pH in the first trial was 3, and for the second trial it was about 4, and for the third trial it was about 3.5, you would calculate a pH average of 3.5 for all trials for 1.5 TUMS.
  2. How did the pH change as you added more powdered TUMS tablets?
    1. How many TUMS quarters did you need to raise the pH of the solution to 3? How many more had you added to raise the pH to 4?
      1. How much calcium carbonate is this in grams? You can calculate this by looking at the back of the TUMS container under "Drugs Facts," in the "Active ingredient (per tablet)" section at the top. 1,000 mg is the same as 1 gram.
    2. After the solution had reached a pH of 4, when you added a total of three more TUMS® tablets what was the maximum pH that the solution reached?
    3. Did it seem as though the solution became saturated after adding a certain number of TUMS? That is, was there a point at which the pH did not go any higher, even when you added more TUMS? If so, why do you think this happened? Do you think this would happen in a real stomach? Why or why not?
  3. Look again at how many TUMS you needed to raise the average pH of the solution to 3 or 4. How does this compare with the recommended dose of TUMS? Look at the back of the TUMS container under "Drug Facts," in the "Directions" section, for the recommended dose.
  4. Make a graph using the data you recorded in the table in your lab notebook. Use the average pH data that you wrote down in step 1. You can make a graph by hand or use a website like Create a Graph to make a graph on the computer and print it.
    1. Put the total number of TUMS you added (in amounts of quarter TUMS) on the x-axis (the horizontal axis) and the corresponding average pH on the y-axis (the vertical axis).
  5. Think about how your esophagus and stomach digest food. If the TUMS primarily dissolves in the esophagus and does not mix much with the liquid in the stomach, do you think it is very important to have the pH of your entire artificial stomach acid solution reach 3 or 4, or do you think a lower pH would result in heartburn relief?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • Think about how your artificial stomach acid solution is different from a real stomach and a real digestive system overall. It may be difficult to modify this science project to mimic more closely what happens in a real stomach, but if you could change it any way, what changes would you make? To learn more about the digestive system, check out this website:
  • In this science project you used TUMS, but there are many other different brands of tablets sold to relieve heartburn. Additionally, while the antacid used in TUMS is calcium carbonate, there are many other antacids available. Repeat this science project using a different brand or an antacid with a different active ingredient. To learn more about antacids, check out this website (it has multiple pages):
    • MEDTV. (n.d.). Antacids. Retrieved September 23, 2011.


If you like this project, you might enjoy exploring these related careers:

Career Profile
Growing, aging, digesting—all of these are examples of chemical processes performed by living organisms. Biochemists study how these types of chemical actions happen in cells and tissues, and monitor what effects new substances, like food additives and medicines, have on living organisms. Read more
Career Profile
Pharmacists are the medication experts. They advise doctors, nurses, and patients on the correct drug dosage for a patient's weight, age, health, and gender; on interactions between drugs; on side effects; on drug alternatives; on costs; and on ways to give drugs. They also dispense drugs at pharmacies, according to prescriptions, checking for dangerous drug interactions, and educating patients on how to take drugs, what reactions to watch out for, and how long it should take for drugs to work. Read more
Career Profile
What do the sequencing of the human genome, the annual production of millions of units of life-saving vaccines, and the creation of new drought-tolerant rice varieties have in common? They were all accomplished through the hard work of biological technicians. Scientists may come up with the overarching plans, but the day-to-day labor behind biotechnology advances is often the work of skilled biological technicians. Read more
Career Profile
Pharmacy technicians play a very important role at a pharmacy. Pharmacy technicians help pharmacists in many different ways. They make sure a pharmacy runs smoothly every day. They may have a role in customer service by taking personal information, answering questions, and taking payments. A technician can measure or mix drugs and package and label containers. They may also count all of the medications to let the pharmacists know if there are low stock items. Pharmacy technicians can work in a… Read more

News Feed on This Topic

, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Calcium Carbonate to the Rescue! How Antacids Relieve Heartburn." Science Buddies, 17 Apr. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/BioMed_p010/medical-biotechnology/calcium-carbonate-how-antacids-relieve-heartburn. Accessed 27 Sep. 2023.

APA Style

Science Buddies Staff. (2023, April 17). Calcium Carbonate to the Rescue! How Antacids Relieve Heartburn. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/BioMed_p010/medical-biotechnology/calcium-carbonate-how-antacids-relieve-heartburn

Last edit date: 2023-04-17
Free science fair projects.