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c
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Communicating
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Testing Antacids
Did you know that your stomach produces between
1 L and 2 L of gastric juice daily? The main
constituent in this juice is hydrochloric acid, and
the pH of a normal stomach is about 1.5
acidic
enough to dissolve magnesium metal! The purpose
of this very acidic medium is to digest food. But the
stomach itself is made of muscle, so why does it not
digest itself? The stomach copes with normal levels
of acidity because it completely replaces its lining
every few days.
However, if the concentrations of acid in the
stomach are too high, problems can occur. Pain,
swelling, inflammation, and bleeding in the
stomach's lining can cause a condition commonly
called acid indigestion. One solution to the problem
is to take a medication that contains an antacid
a
mild base that can neutralize acid. The typical bases
found in common antacids are listed in Table 1.
IEEEII
Antacids and Their Ingredients
calcium carbonate
calcium carbonate
Deslgn
You will react a measured mass of baking soda with
hydrochloric acid of roughly the same pH as
stomach acid. You will then react a measured mass
of an antacid with hydrochloric acid and compare
the acid-neutralizing effectiveness of the baking
soda and the antacid.
(b) Design
a table
to record all your observations,
Materials
.
'
.
.
'
'
.
.
'
'
.
.
.
apron
safety goggles
sodium bicarbonate (baking soda)
balance
100-mL beakers
water
1O-mL graduated cylinder
universal indicator, with colour chart
stirring rod
hydrochloric acid solution (2,5o/o or 0.3 mol/L,
pH roughly 0.5)
microdropper
various antacid tablets
mortar and oestle
magnesium hydroxide, aluminum hydroxide
Hydrochloric acid is corrosive. Any spills
on the skin, in the eyes, or on clothing
should be washed immediately with
plenty of cold water. Report any spills to
your teacher.
magnesium hydroxide
A typical pharmacy may offer 30 different
antacids to choose from. \{hich one do you choose?
Consumer Reporthas hired you to answer that
question.
Question
How do antacid tablets compare in their acidneutralizing ability to baking soda? Are all antacid
tablets equally effective?
Frediction
(a) Make predictions to answer the Questions.
320
Chapter 8
Procedure
$
Put on your apron and safety goggles.
H
Measure 2 g of baking soda into a 100-mL
@
beaker.
E
Add 5 mL of water and a few drops of universal
indicator.
tr
While stirring the baking soda with the stirring
rod, add hydrochloric acid slowly using a
microdropper. Count the number of drops you
sxlfis x*ilnBosx: @
Uring a Mass Balance
- -: :.-..: - :--* -:-.-- ". - I::--- : ,ll
._
..:,
-...-.: . ..-. -^
l,-,.;.:u
LI]Cl.iIt'f
---- *---.-:\;'
- - :'
<i;--- r- .i--,
,
;- -:- *. .;-:.-.::a
d.op, of acid that u-ouid be neutralized
bl' 1 g of each antacid. Use the following
in \-our data table. re.ord the mass oi baking
and the number oi drops oi acid
'oda
equation:
required.
drops/gram =
E
Determine the mass of an antacid tablet. Crush
the tablet to a fine powder with a mortar and
pestle (Figure 1). Transfer a measured mass
(between I and 2 g) into a 100-mL beaker.
Repeat steps 3 and 4 for the antacid tablet.
(d) In your data table, record the antacid tablet's
name) total tablet mass, mass of tablet
reacted, and number of drops of acid
required.
:.1- -l.iil:Da:
lf
-llifi.
mass
drops of acid
of antacid reacted (g)
(h) To compare the neutralizing ability by
tablet, calculate the number of drops that
would be neutralized by one tablet using the
following equation:
drops/tablet = drops/gram x mass of tablet (g)
(i) Prepare your summary for Consumer
@ Report.Include your results in the form of
@ bar graph.
a
Understand ing Goncepts
l.
Given your results, which antacid tablet would yoconsider taking if you had an acid stomach problem?
Explarn.
2.
Why did you stop the neutralization at pH 2 rather than
at pH
7?
Making Gonnections
@l
3. (a) Would
you want an antacid to dissolve in your
stomach instantly 0r over a perrod of time? Explain.
(b) What
is one possible advantage of liquid medicines
over solid medicines?
$l
f|
Repeat step 5 for the other antacid tablets
provided by your teacher.
Dispose of the mixtures in the beakers, and
clean and put away your materials as instructed
by your teacher. Clean up your work station.
Wash your hands.
{c) What
(d) What other variables would
(")
(f)
\Mhy is it necessary to stir the mixture as the
acid is added?
\{hy did the colour of the indicator change
when the acid was added?
@Evaluating @Graphing
you consider, when
choosing an antacid?
Exploring
4.
Analysis and Evaluation
is one possible advantage of solid medicines
over liquid medicines?
Another issue in deciding whether 0r not t0 purchase
a
product is price. Find out the price of the antacrds per
tablet, per gram, 0r per recommended dosage. Analyze
and rennrt nn thc nnst value of various brands of
anTac | 0s.
Acids and Bases 321