Advanced Chemistry Titration Lab
Your objective in this lab is to evaluate the cost effectiveness of four brands of
antacid tablets. You will design, perform, and document the procedure and analyze and
present the results.
Antacids neutralize (or buffer) the excess hydronium ion, H30+, (H+) in stomach
acid to relieve this discomfort. The amount of antacid needed for relief is dependent
upon its “strength” which is based on its ingredients. The formulations of some common
antacids are listed below.
Common Antacids
Principal Active Ingredient(s)
NaHCO3/citric acid
Mg(OH)2/Al(OH)3
CaCO3/Mg(OH)2
CaCO3
Al(OH)3/MgCO3
Al(OH)3/MgCO3/Mg(OH)2
Representative Antacid
Alka Seltzer
Mylanta
Rolaids
Tums, Equate
Gaviscon
Di-Gel
The advertised antacids that buffer excess acid in the stomach are those containing
calcium carbonate, CaCO3, or sodium bicarbonate, NaHCO3. These antacids establish
the HCO3-/CO32- buffer system in the stomach.
CO32-(aq) + 2H30+(aq)  HCO3-(aq) + 2H2O(l)
Antacids, like Rolaids, that also contain Mg(OH)2 or Al(OH)3 are a combination antacid
that also reacts with stomach acid.
Mg(OH)2(aq) + CaCO3(aq) + 3H3O+(aq)  Mg2+(aq) + Ca2+(aq) + 5H2O(l) + HCO3-(aq)
The antacids you will use are as follows:
____________________________________________________
Price
Quantity
Dosage
(# tablets)
(# tablets)
Rolaids
$
150
2-4
Equate
$
150
2-4
Tums
$
150
2-4
Alka Seltzer
$
36
2
Mylanta
$
355mL
2-4 teaspoons
(1 tsp = 5mL)
____________________________________________________
You will need to make a standard sodium hydroxide solution. You will also need to
make a standard hydrochloric acid solution of about 0.1M (since that’s about what your
NaOH standard is). I will provide 3M HCL for you to dilute. I recommend you titrate
your final HCl solution to check your dilution. As for indicators there is phenolphthalien
and bromophenol blue.
Because you will be dealing with substances that form buffer solutions, you will be using
a "back titration" process to evaluate effectiveness of the antacid. This process is
described below.
Determine a way to evaluate the effectiveness of each antacid and relate the
effectiveness to cost. Document your procedure, data and results in the form of a typed
memo to me. Show all your calculations in a neatly handwritten attachment to the memo.
Procedure for Standard NaOH solution:
You are to complete at least three trials in the standardization of your NaOH solution. To
hasten the analysis, clean, dry and label three 125 mL or 250 mL Erlenmeyer flasks and
measure the mass of three KHC8H4O4 samples (see below). If all the balances are
occupied, prepare your NaOH solution first.
This is an analytical experiment; you are striving for “good” results. The measured molar
concentration of the NaOH for the three trials should be within ±1%. If not, a fourth or
fifth trial may be necessary.
Preparation of NaOH solution
Using a 10-mL pipet, carefully transfer 10 mL of the concentrated NaOH solution to a
500-mL polyethylene bottle. (Caution: a concentrated NaOH solution causes severe
burns) Dilute to approximately 500 mL with previously boiled, distilled water. Boiling
the water removes traces of CO2. Stir the solution for several minutes (Do not shake the
bottle; this increases the probability of CO2 absorption.) Cap the polyethylene bottle to
prevent absorption of CO2 by the NaOH solution. Label the bottle.
Preparation of KHC8H4O4 samples
Measure 0.3 – 0.5g (±0.001g) of the dry KHC8H4O4 and place in a clean, dry 125-mL or
250-mL Erlenmeyer flask. Add 50 mL of distilled water and 3 drops of phenolphthalein.
Determination of NaOH solution Concentration
Prepare a buret for use with the NaOH solution as the titrant. Record the starting level of
the buret.
Titrate the KHC8H4O4 sample to its endpoint. Record the ending level of the buret.
Calculate the concentration of the NaOH solution using the mass of KHC8H4O4 and the
volume of NaOH solution used in the titration.
After completing titrations of all three samples, compare the molarities calculated for
each sample. If the molarities are within ±1% of each other, average them for the final
molarity of your standard NaOH solution. Label the polyethylene bottle with the
averaged molarity.
Back Titration
In back titration, what we are essentially doing is reacting a known amount of the antacid
with a known amount of acid. We continue doing this until the antacid will no longer
neutralize the acid (ie., there is excess acid in the flask). Then we titrate the acid in the
flask to determine its quantity, thus determining the quantity of acid that the antacid
neutralized.
Basically:
Since an antacid has the same neutralizing effect on stomach acid as does NaOH, the
amount of antacid in a sample is called its NaOHequivalent. To determine the NaOHequivalent
for an antacid, we subtract the excess moles of HCl(aq) from the total moles of HCl(aq)
added to the antacid.
NaOHequivalent = HCl(aq)total – HCl(aq)excess
General Procedure:
1. Add 25.0 mL of standardized HCl into the flask containing the antacid and swirl to
dissolve the antacid.
2. Slowly heat the solution to boiling and continue to heat at a gentle boil, for at least 1
minute, to expel dissolved CO2. Add 4-8 drops of bromophenol blue indicator. If the
solution if blue, add an additional 15.0 mL of HCl and boil again. Continue adding HCl
until the solution turns yellow. (Record the total amount of HCl added.)
3. Titrate the solution to the blue endpoint of the bromophenol blue indicator to
determine the amount of excess HCl.
Rubric for Antacid Analysis Lab
NAMES:
MEMO:
Procedure Documented
Data Provided
Effectiveness related to cost
Methodology appropriate
Conclusion provided/supported by data
CALCULATIONS
Organization
Completeness
Units
Methodology/results supported by calcs
RAW SCORE (18 points possible)
Raw Score x 5 = TOTAL SCORE