Activity 2
Antacids in the Stomach
7HAT$O9OU3EE
GOALS
What Do You Think?
In this activity you will:
People may eat too much of various foods that will work together to
cause an upset stomach, acid indigestion, or heartburn.
• Explore the chemical
environment in the stomach,
especially how it responds in
the presence of bromophenol
blue indicator.
• Observe how commercial
antacids work in the stomach.
• Experimentally determine
whether equal masses of
different antacids have equal
ability to lower the acidity of a
sample, and thereby determine
which one is the most effective.
• How does taking an antacid relieve the discomfort that accompanies
these digestive problems? Do they work?
Record your ideas about these questions in your Active Chemistry log.
Be prepared to discuss your responses with your small group and the class.
Investigate
1. Add 2 mL 0.5 M hydrochloric acid to each of four test tubes.
(Hydrochloric acid will be used to simulate stomach acid.)
2. Place one drop of bromophenol blue indicator in each test tube.
a) What is the color of the indicator when it is in the presence of
the acid?
Safety goggles
and a lab apron
must be worn
at all times in a
chemistry lab.
3. The question you will investigate is: How will the acid, similar to
what is in your stomach, react when different bases are added to it?
Bases are the active ingredients of antacids.
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4. To the first test tube, add some of
the base called sodium bicarbonate,
NaHCO3.
a) Observe and record what
happens. Is there a color change
after the base has been added?
What is the color of the indicator
when an excess of antacid has
been added? Did any other
change occur?
5. Add some ground-up calcium
carbonate antacid tablets to the
second test tube.
a) Observe and record what
happens.
6. Add some liquid antacid to the
third test tube.
a) Observe and record what
happens.
Be careful with
the acid used
in this activity.
It can cause
chemical burns.
Do not eat
anything used in
the lab.
Dispose of
the chemicals
carefully as
your teacher
instructs.
Wash your
hands and arms
thoroughly after
the activity.
b) In your Active Chemistry log,
describe what seems to be
consistent about the color of
the indicator when it is in the
presence of an acid and when it
is in the presence of a base.
7. Save the fourth test tube with its
acid and indicator as a comparison
to use in the following part of the
activity.
8. Grind up the three commercially
available antacids. Measure out
0.25 g samples of each.
a) Record the cost of the bottle and
the number of doses per bottle.
Use this information to calculate
the price per dose. Be aware that
for some products, a dose may
require more than one tablet.
9. Place the 0.25 g of each antacid
into a small plastic cup that has a
volume of about 150 mL.
10. Add 20 mL of water to each
container. Then add 10 drops of
bromophenol blue indicator to
each container.
a) Observe and record the color of
the solution in each container.
11. Using an eyedropper, slowly add
0.50 M hydrochloric acid to the
mixture of water and antacid.
Carefully count the drops of
hydrochloric acid that are required
to change the color of the indicator
to the color it had in acid solution.
(Remember, you saved the fourth
tube for this purpose.)
You will need to swirl the container
and solution after each addition of
the acid. Some of the antacids will
change color but will turn back to
the original color in a few seconds.
You must continue to add acid and
swirl until the new color remains for
at least 60 seconds.
a) Record the final number of drops.
b) Use the data you collected to
decide which antacid provides the
most neutralizing power. Discuss
what evidence you used to make
this decision.
c) Which is the most economical
antacid to use?
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Activity 2 Antacids in the Stomach
Chem Words
ANTACIDS
Is It Heartburn or Acid Indigestion?
Why are there so many commercials for antacids on TV? One reason
is that almost 50% of the population in the U.S. has heartburn at
least once a month, and 7% experience it every day. Statistics on acid
indigestion are difficult to find because the definition is vague, but it’s
probably almost as common as heartburn.
antacid: a substance that
will increase the pH in
the stomach.
acid: a solution that has
a pH less than 7.
base: a solution that has
a pH greater than 7.
Heartburn is the burning feeling in the middle of your chest caused
by acid leaking upwards from the stomach into the esophagus. Your
esophagus doesn’t have a protective lining like the stomach. The acid
leaking up into the esophagus can cause pain and sometimes even
damage. Even though it is called heartburn, it has nothing to do with
your heart. The pain is experienced in the general area of the heart.
Like heartburn, acid indigestion causes a similar burning
discomfort, but it is in the pit of your stomach. The entire
surface of the stomach is covered with a mucus lining
that protects the stomach from the corrosive effects of
the acid. However, this protective layer sometimes breaks
down and results in the feeling of acid indigestion. Severe
damage to the stomach lining can result in an ulcer. An
ulcer is a lesion in the surface of the lining of the stomach.
Until recent times, doctors believed lifestyle factors like
stress and diet caused ulcers. Although it is true that
smoking, drinking alcohol, and using caffeine are still
suspected of causing problems, scientists now believe that
the primary cause of most ulcers is infection caused by the
bacterium Helicobacter pylori (H. pylori).
pH in the Stomach
An empty stomach has a pH of about 1 to 2 and is therefore very
acidic. (Recall that solutions with pH values less than 7 are acids and
those greater than 7 are bases.) When foods are consumed, the pH
will change and cause the contents in the stomach to be less acidic.
For instance, the pH might rise to 4. The bromophenol blue indicator
that you used has different colors depending on the acidity of the
solution. If the pH is 3 or less, the indicator solution will be yellow.
Ulcers are open sores that
develop on the lining of
the esophagus, stomach,
or upper small intestine.
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If the pH of the solution is 4.6 or greater, it will become a purple color.
Notice that between 3 and 4.6, it will be changing colors.
Relieving Heartburn and Acid Indigestion
Those who suffer from more than occasional heartburn sometimes find
the need to take steps to prevent stomach acid from leaking back up
into the esophagus. Avoiding alcohol, peppermint/spearmint, chocolate, all
caffeinated drinks, and fatty foods helps maintain the proper connection
between the esophagus and the stomach. Waiting
two or three hours after eating before lying down
is also recommended. To prevent acid indigestion
and to protect the stomach lining, aspirin and
tobacco products should not be used. To reduce
the production of extra acid, smoking, caffeinated
products, citrus juices, and milk (yes, milk) should
be avoided.
There are two types of over-the-counter
medicines proven to work against heartburn and
acid indigestion. They are antacids and hydrogen
blockers. They both reduce the acidity of stomach
fluids. Antacids work quickly and are relatively
cheap. They do not stop the production of the
acid. They simply use up the excess stomach acid
to provide a short period of relief.
One active ingredient in some antacids is calcium carbonate CaCO3.
This ingredient is often found in chewable antacid tablets. Calcium
carbonate is a solid (s) that reacts with some of the hydrochloric acid
(HCl), a liquid (aq). The products of this reaction are calcium chloride,
water, and carbon dioxide (CO2), a gas (g). The reaction is:
CaCO3(s) ⫹ 2HCl(aq) → CaCl2(aq) ⫹ H2O(l) ⫹ CO2(g)
Another active ingredient, magnesium hydroxide, is also able to react
with the hydrochloric acid in the stomach. This active ingredient is
frequently found in many of the liquid antacids. The reaction is:
Mg(OH)2(s) ⫹ 2HCl(aq) → MgCl2(aq) ⫹ 2H2O(l)
A third active ingredient commonly found in antacids is aluminum
hydroxide, which also reacts with the hydrochloric acid. The reaction is:
Al(OH)3(s) ⫹ 3HCl(aq) → AlCl3(aq)⫹ 3H2O(l)
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Activity 2 Antacids in the Stomach
In this activity, the color of the acid-base indicator tells you the pH
of the stomach acid. When the antacid was added it neutralized some
of that acid and the pH of the mixture changed. The pH went up and
changed the color of the indicator. You saw that all of the antacids
changed the color of the indicator. In the first equation on the preceding
page, the calcium carbonate, CaCO3, used up the hydrochloric acid
(HCl) and made carbon dioxide (CO2), calcium chloride (CaCl2), and
water. But in the other two equations, the active ingredient in the
antacid actually neutralized the acid. This means that the number of
molecules (or moles) of acid consumed equals the number of molecules
(or moles) of water produced. Even though the different types of
antacids reacted in different ways, they all lowered the amount of acid
and made the pH go up. This was shown by the change in color of the
indicator. An indicator is one simple way to show that the amount of
acid is changing. Remember that as the acidity goes up, the pH goes
down, and as the acidity goes down, the pH goes up.
After taking an antacid, a smaller amount of acidic gastric fluid will
reflux into the esophagus, causing less heartburn. As you have seen
in this activity, different products have different abilities to reduce the
acid concentration. Part of this depends on which active ingredients
the product contains. The other factor deals with how much of each of
the ingredients a particular product contains. Reading the label can help
explain which reactions are going on in the stomach.
Hydrogen blockers, rather than neutralizing some of the acid like
antacids do, actually reduce the amount of acid being produced in the
stomach. However, the only way for the blocker to do this is to be
absorbed through the intestine and into the blood stream. This takes
longer than an antacid to work, but the hydrogen blocker will provide
relief longer than an antacid (6–12 hours).
The obvious question is, “Why not put both an antacid and a hydrogen
blocker in the same product?” That way a person could get temporary
relief from excess acid as well as future reduction in the production
of acid. It would appear that you are thinking in the same way as the
big drug companies. At least one product now available, has done just
that. It contains calcium carbonate and magnesium hydroxide along
with a hydrogen blocker, which is used to restrict the production of
hydrochloric acid.
Chem Words
acid-base indicator: a
substance that changes
color when exposed to
either an acid or a base.
hydrogen blocker: a
compound that is used
to inhibit the production
of hydrogen ions in the
stomach and intestines.
Checking Up
1. What are the
differences between
heartburn and acid
indigestion?
2. What is an ulcer?
3. a) How do antacids
work against
heartburn and
acid indigestion
differently?
b) How do hydrogen
blockers work
against heartburn
and acid indigestion
differently?
4. Lowering the
concentration of acid
has what effect on the
pH of a solution?
5. Which type of product
produces relief from
heartburn and acid
indigestion faster,
antacids or hydrogen
blockers? Explain.
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What Do You Think Now?
At the beginning of this activity you were asked:
• How does taking an antacid relieve the discomfort that accompanies these
digestive problems? Do they work?
Now that you have completed this activity, how would you explain the purpose
of antacids and how they work? Are all antacids the same in chemical composition
and in their ability to neutralize acids?
What does it mean?
Chemistry explains a macroscopic phenomenon (what you observe)
with a description of what happens at the nanoscopic level (atoms
and molecules) using symbolic structures as a way to communicate.
Complete the chart below in your Active Chemistry log.
MACRO
What observations did you use
to determine the general acidity
of the different solutions tested?
NANO
At the molecular level, what
is the reaction between the
hydrochloric acid HCl and
the sodium bicarbonate base
NaHCO3?
SYMBOLIC
In chemisty, you can use
equations to represent
reactions. Use equations to
show how the hydrochloric
acid of the stomach can be
neutralized.
How do you know?
Antacids are advertised to reduce the acid in your stomach.
What evidence do you have from the activity that this is true?
Why do you believe?
You or someone you know may have experienced the discomforts
of acid indigestion. What do people you know do to relieve acid
indigestion? (Note: Relief from acid indigestion may not involve the use
of a drug at all. It may involve preventative steps you can take to avoid
these problems.)
Why should you care?
Finding ways to avoid acid indigestion or heartburn are important.
If these conditions occur often you can expect to have more serious
problems at a later time of life. How can you incorporate this into
your presentation?
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Activity 2 Antacids in the Stomach
Reflecting on the Activity and the Challenge
In this activity, you expanded your knowledge about acids, antacids, bases, and
indicators. The stomach contains gastric fluids, which are mostly hydrochloric
acid, and antacids may be used to neutralize this acidity. In this activity, you
examined various antacids and their abilities to neutralize hydrochloric acid.
This information could come in handy as you plan your skit as part of the ride
down the alimentary canal.
Imagine what might happen if all of a sudden some antacid dropped into
the stomach where you were trapped. Would something different happen if it
were a calcium carbonate tablet as compared to a dose of aluminum hydroxide
or magnesium hydroxide? Remember, in your skit you must represent what
is chemically occurring by acting out the roles that the individual molecules
would play.
1. Write a balanced chemical equation for the neutralization reaction between
sodium hydrogen carbonate (sodium bicarbonate) and hydrochloric acid.
(Hint: One of the products is the gas discussed in Activity 3.)
2. What simple method can be used to identify an acid or base?
3. Classify the following household products as acidic or basic based on their pH.
a) Vinegar, pH 3.0
b) Drain cleaner (contains sodium hydroxide), pH 12.0
c) Tomato sauce, pH 4.4
d) Household ammonia, pH 10.0
e) Citric juices, pH 3.0
f) Baking soda, pH 9.0
4. It takes twice as much of antacid X as antacid Y to neutralize a certain mass
(or volume) of an acid. Which antacid contains more base?
5. Solution A is tested with blue litmus paper. It stays blue. Solution A is then
tested with red litmus paper. The red litmus paper stays red. What can you
conclude about the solution?
6. Create a chart like the one below in your Active Chemistry log and record the
information gathered by reading the labels of different antacid products at a
grocery or drug store:
Ingredients
Antacid #1
Antacid #2
Antacid #3
recommended dose
cost per container
cost per recommended dose
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7. Preparing for the Chapter Challenge
Create a few lines of exciting dialog that can be used to describe what happens
in the stomach as the antacid is ingested. Is there a way you can include a
chemical equation into your ride or dialog?
Inquiring Further
1. Choosing relief for an upset stomach
If you were traveling through the alimentary canal and the stomach was upset,
would you want your host body to calm the stomach down with a dose of
magnesium hydroxide, sodium bicarbonate, or calcium carbonate?
2. Structure and function of the stomach
Research the structure and function of the stomach. What controls the movement of
food into and out of the stomach? What is the pH of gastric fluids? In addition to
acid, what other fluid is secreted in the stomach? What protects the stomach lining
from the acid?
3. GERD (gastroesophageal reflux disease)
Research and report to your team about acid-reflux disease (GERD).
4. Definitions of acids and bases
What are the definitions of acids and bases according to Arrhenius, Brønsted and
Lowry, and Lewis? Review your previous work with acids and bases and summarize
these definitions.
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