DIGESTIVE SYSTEM-ACIDS AND BASES
NEUTRALIZATION AND HEALTHY DIET
Experiment Objective:
Students will examine acid-base chemistry and
neutralization of stomach acids in a mini plastic stomach.
Learning Goals:
Students will observe first hand acid and base properties
in the food they consume everyday. Students will test the
pH of these foods/liquids and learn the simple method of
neutralizing stomach acids with base and antacids. Students
will be able to explain the importance of acid-base balance.
LESSON IMPLEMENTATION OUTLINE
Introduction:
When you eat foods—such as bread, meat, and vegetables—they are not in a form that
the body can use as nourishment. Food and drink must be changed into smaller molecules
of nutrients before they can be absorbed into the blood and carried to cells throughout the
body. Digestion is the process by which food and drink are broken down into their
smallest parts so the body can use them to build and nourish cells and to provide energy.
Digestion involves mixing food with digestive juices, moving it through the digestive
tract, and breaking down large molecules of food into smaller molecules. Digestion
begins in the mouth, (chew and swallow), and is completed in the small intestine.
Content Background:
The stomach is like a mixer, churning and mashing together all the small balls of food
that came down the esophagus into smaller and smaller pieces. It does this with help from
the strong muscles in the walls of the stomach and gastric juices that also come from the
stomach's walls.
The stomach is attached to the end of the esophagus. It's a stretchy sack shaped like the
letter J. It has three important jobs:
1. to store the food consumed.
2. to break down food into a liquid mixture with acids
3. to slowly empty that mixture into small intestine
In order to aid in the digestion of food and to protect
your stomach against bacterial growth, the stomach
secretes gastric acid consisting mainly of hydrochloric
acid at a pH of about 2. The stomach is protected by a
mucous lining which can be damaged if the acidity
becomes too high, possibly causing an ulcer. Heartburn,
indigestion, or upset stomach is also a result of too
much acid in the stomach. For many people, acid indigestion can originate from eating
too much, eating too quickly, eating high-fat foods, or stressful situations.
Treatment of indigestion involves lowering the production of stomach acids or
neutralizing the acid. Antacids, such as Tums and Rolaids, neutralize acid in the stomach
raising the pH level to between 3 and 4. This can significantly relieve symptoms for most
people. Antacids provide relief more quickly and are less expensive than other
medications. Most antacid products contain active ingredients, which are alkaline (or
basic) that react with acid during neutralization.
Neutralization reaction is one in which an acid loses its acidic qualities and a base loses
its alkaline qualities. After neutralization reaction an acid is no more acidic and a base is
no more basic. They become neutral like water.
Lab Activity Instructions:
Students will perform the stomach acids and neutralization experiment individually and
can work together with others during the experiment. Instructors will explain with the
materials for the experiment and briefly demonstrate the steps. Allow one instructor for
presentation and other instructors as assistants around the lab.
Materials:
milk, vinegar, lemon juice, apple juice, pop, baking soda, antacid (Tums or Rolaids),
plastic Ziploc bags, cabbage juice indicator, pH litmus paper, antacid tablets, mortar,
pestle, labels, measuring spoons, water, rubber gloves, goggles, scrap paper, pencils,
picture of the human digestive system
Procedure:
1. Obtain a Ziploc bag and label with your name. The Ziploc bag represents the
stomach where food will be stored and processed.
2.
3.
4.
5.
6.
7.
Select two types of food to use for the experiment. Use a small litmus paper and
test to see if the food/liquid is an acid or a base. Record this information on a
piece of paper.
Use a measuring spoon and place one tablespoon of each food/liquid into the
Ziploc bag. Close the bag and shake the food/liquid lightly to mix. Test the pH of
the mixture and record on the paper whether it is acidic or basic.
Use a mortar and pestle to grind up the antacids.
Add a few drops of the cabbage indicator into the Ziploc bag and mix well.
Slowly add a tablespoon of antacids to the mixture. Compare the colour of the
solution to the cabbage juice indicator reference sheet to see if the solution has
been neutralized (close to pH 7). Neutralization has occurred if the colour of the
food mixture is similar to the colour of cabbage juice indicator at pH 7.
Continue to add antacids and experiment until neutralization has occurred. Add
water to see if it changes the pH.
Red Cabbage Juice Indicator
Checking for student understanding:
Ask students questions during the lab about neutralization and question them about
adding water and its effect on the pH of the mixture. Check students’ experimental
stomach to see if they understood the neutralization process.
Extensions and connections:
Reflect on the type of food and liquid you consume at each meal. Are they acidic or
basic? How do they affect your digestion?
Curriculum Concept:
Health Education –Basic functions of digestive systems and stomach acids
References:
http://www.uen.org/Lessonplan/preview.cgi?LPid=510
http://www.digestive.niddk.nih.gov/ddiseases/pubs/yrdd/#why
http://www.galaxy.net/~k12/body/digest.shtml
http://www.kidshealth.org/kid/htbw/digestive_system.html
http://www.poopreport.com/Doctor/Knowledgebase/what_happens_to_stomach_acid.htm
RED CABBAGE JUICE INDICATOR CHART
COMMON ACIDS AND BASES
DIGESTIVE SYSTEM