Testing and Comparing Antacids
Theory:
The stomach contains hydrochloric acid, which is used in the
digestion of foods. The acid is released, as needed giving the
stomach a pH range of 0.9 to 2.0. If too much acid is released
the pH may lower too much and cause discomfort, which is commonly,
called “acid indigestion”. Antacids can be used to neutralize
this excess acid.
Most antacids are only slightly soluble in water and are made to
dissolve slowly in the stomach acid so that carbon dioxide is
released gradually. They contain weak bases as sodium bicarbonate
(NaHCO3), calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2),
aluminum hydroxide (Al(OH)3) or combinations of these. Reactions
are given below:
NaHCO3 (s) + HCl (aq)  NaCL (aq) + H2O (l) + CO2 (g)
CaCO3 (s) + 2 HCl(aq)  CaCl2 (aq) + H2O (l) + CO2 (g)
Al(OH)3 (s) + 3HCl(aq) - AlCl3 (aq) + 3H2O(l)
Mg(OH)2 (s) +2HCl(aq)  MgCl2 (aq) + 2H2O(l)
Purpose:
In this lab you will be testing a number of common antacids.
Using the method of titration, you will neutralize the excess
acid. Methyl orange will be the indicator. It changes color
between pH of 3.0 (red) and 4.4 (yellow) (note both are in the
acid range). In this experiment and pH of 3.0 is a reasonable pH
value to use as an endpoint to indicate the excess has been used
up and returns the stomach to a “normal” pH. You should look up
the cautions for each of these solid or liquid antacids.
Materials:
Milk of Magnesia (MOM)
Generic
Tums
Rolaids
Methyl orange indicator
Universal indicator
0.5M HCl
mortar and pestle
pH indicator strips
stirring rod
beral pipets
Erlenmeyer flasks (2 or 3)
graduated cylinder 25-mL
50-mL buret
Safety:
Do NOT eat any of the samples. Methyl orange is toxic.
indicator is flammable. Wear goggles.
Universal
Procedure:
See the end of the lab for the data tables that you will need to
copy.
Part I
1.
Fill a 400-mL beaker about 1/2 full of distilled water.
2. Add 2 ml of universal indicator. (use marked pipet)
3. Add 6 drops of 0.5 M HCl. This will be the “upset” stomach
solution. Record the color of the solution in you Table I (found
at the end of the lab). Also record the approximate pH using the
universal indicator chart.
4. Using a mortar and pestle, grind up a MOM tablet. If you only
have liquid, measure out 1 teaspoon. Add this to the beaker and
stir. Observe for a few minutes and record your observations in
Table I.
5. When the solution is not changing color anymore, add 2-3 more
drops of the HCl. This represents the antacid reacting with the
antacid as the stomach produces more HCl. Record your
observations.
6.
Rinse the solution down the drain with plenty of water.
Part II
A. Prepare a control (if one is not already out on the lab table)
by putting 25 ml of distilled water into a 125-mL Erlenmeyer
flask. Add 20 drops of 0.5M HCl to the flask, 10 drops of methyl
orange indicator and mix well.
Note the color of this acidic solution and use it as control
(color comparison) during your titrations. Do not discard.
B.
1.
the
2.
Choose an antacid table and record the brand in Table 2.
Weigh the table on a balance that reads to 0.01 grams. Record
mass in the table.
Using a mortar and pestle, grind into a powder.
C. Prepare solution for the titration:
3. Measure out 25-mL of distilled water and pour into an
Erlenmeyer flask.
4. Using a spatula, scrap the powdered tablet into the flask and
stir. (Note: It will not fully dissolve.)
5. Determine the pH of this solution by dipping the stirring rod
into the solution and touching the pH paper. Record in table 2.
6.
Add 10 drops of methyl orange, swirl and record the color.
7. Fill your buret with 0.5M HCl. Record the initial volume.
Begin titrating by dispensing 5-mL aliquots, swirling after each
addition. Occasionally rinse the sides of the flask with
distilled water.
8. After about 15 ml change your additions to 1 ml aliquots. As
it approaches the color of your standard and drops more carefully
so as not to pass the endpoint. When you think you are at the end
of the titration, test the solution with pH paper. The color
should remain “red”. The final solution should be near or below a
pH
of 3.
9. Read the volume off the buret and record. Also record the
final pH.
10.
Rinse the solution down the drain using plenty of water.
11.
REPEAT steps 1-10 with a different antacid tablet.
**GO DO WEBASSIGN**
DATA/OBSERVATIONS
Copy these into your lab notebook!!
Table I (part I)
Step # Type environment
3
Upset stomach
4
5
Observations
Antacid introduced into
The stomach
Additional HCl added
Table II (part 2 – titration)
Antacid brand 1 Antacid brand 2 Antacid brand 3
Mass of Tablet (g)
pH of solution
before titration
Color of solution
before titration
Starting volume
of HCl, mL
Ending volume
of HCl, mL
Color of solution
after titration
pH of solution
after titration
Table III (summary of data and calculations)
Make a chart to put in the calculations for each of the 3 brands
you used.
CALCULATIONS (and summary of data)
Show the work your calculations for ONE of the samples. Put those
and the answers for the other 2 samples in the table you made for
these results.
In your Table III include the following:
Volume of HCl used per tablet
Mass of the table used (g)
Volume of HCl neutralized per gram of tablet (mL/g)
Price per bottle of antacid
Number of antacid tablets per bottle
Cost per tablet (in cents)
Cost per gram (cents/g)
Cost per mL of HCl neutralized (cents/mL)
Volume of HCl neutralized per penny (Ml/cent)
Active ingredient(s)
Amount of each active ingredient (mg/tablet)
Recommended adult dosage (# of tablets)
QUESTIONS
1. Why was methyl orange chosen as the indicator for this
titration?
2. Which antacid tested is most effective at neutralizing stomach
acid?
Answer in terms of “per tablet” and “per gram” of antacid. Use
your
data to support your answer.
3. Which antacid is most cost effective?
(Don’t forget to take into account the # of tablets needed per
dose.)
Reference:
Flinn Scientific Inc, How Powerful is Your antacid, publ. # 1741