Acid-Base Titration with Antacids
Strong soluble bases likes NaOH would certainly neutralize the acid in our stomach but it would also destroy the lining of the
mouth and esophagus on the way down. There are several dangers in taking too much antacid into your system. One danger is
described as the “acid rebound effect”. This is when the stomach acid is neutralized the acid-secreting cells of the stomach will
produce more acid. A second danger lies in those antacids which contain magnesium ions. Magnesium ions are strong
purgatives and abuse leads to chronic diarrhea and dehydration.
Objective: Uses a microscale technique to quickly test various brands of antacids in order to determine the best buy among the
different brands tested.
Safety Concerns: All normal safety rules apply to this lab. Special concerns deal with handling the acid and base solutions as
well as glassware.
Materials
Mortar and pestle
Filter paper
10 mL graduated cylinder
0.10 M HCl
0.010 M NaOH
100 mL graduated cylinder
beral pipets
stirring rod
antacid tablets
funnel
microwell plate
two 150 mL beakers
phenolphthalein
Procedure
Making the HCl/antacid Stock Solution
1.
Obtain one dose of an antacid brand selected for your group from your instructor. It is not necessary to mass the
tablet(s). Grind the tablet using a mortar and pestle and add the powder to a clean beaker.
2.
Obtain 75.0 mL of the microscale acid solution. Use some of the acid solution to rinse the mortar, adding all the liquid
solution to the powder in the beaker.
3.
Obtain 25.0 mL of distilled water in your graduated cylinder and use that water to rinse the mortar one final time. Add
the rinse to the beaker. Stir and swirl the solution using only hand warmth to heat the beaker.
4.
Filter the solution and place the final HCl/antacid solution in a clean 150 mL beaker marked for your antacid brand.
Titrating the HCl/antacid Solution
5.
Obtain approximately 6.0 mL of the HCl/antacid acid solution using a 10 mL graduated cylinder.
6.
Add 15 drops of the acid solution to the large well on the spot plate using your transfer pipet. Make certain you use
proper technique when using the pipet (clean, held vertically, same volume drops, no air bubbles, etc.)
7.
Add 1 drop of phenolphthalein to the acid solution.
8.
Titrate with the NaOH in the marked dropping bottles until endpoint, counting the number of drops used. Record the
number of drops needed. Be certain you are stirring with the clean glass end of the stirring rod. It must be cleaned after
each use.
9.
Repeat steps 6-8 two additional times.
10. Repeat steps 5-9 with as many other brands of antacids as possible till clean-up time is called. At that point you must
clean all equipment for the next class.
Calculations:
1. Determine the average number of drops of NaOH needed to reach the endpoint for the 3 trials for each type of antacid tablet.
2. Use the cost of the antacid package and the number of doses per package to calculate the cost per dose.
3. Develop an effectiveness rating combining the cost and efficiency at neutralizing the acid solution. This mathematical rating
requires creative thinking as well as sound mathematical reasoning. Realize that this rating is the most important and the most
difficult to develop. You must help the consumer decide what your data shows (i.e., which antacid works the best, is the best per
cost, overall, etc.)
General notes:
Brand
Tablets/Dose
Costs
Active Ingredients
Tums
2 tablets/dose
36 tablets
$2.99
1000 mg CaCO3/ tablet
Tums EX
1 tablet/dose
80 tablets
$5.79
750 mg CaCO3/ tablet
Equate
1 tablets/dose
96 tablets
$2.23
750 mg CaCO3/ tablet
Rolaids
1 tablet/dose
150 tablets
$4.99
550 mg CaCO3, 110 mg
Mg(OH)2/ tablet
Rolaids (extra strength)
1 tablet/dose
100 tablets
$4.99
675 mg CaCO3, 135 mg
Mg(OH)2/ tablet
Maalox
1 tablet/dose
90 tablets
CVS (extra strength)
1 tablet/dose
96 tablets
$4.29
750 mg CaCO3/ tablet
CVS (regular)
2 tablets/dose
150 tablets
$4.29
1000 mg CaCO3/ tablet
Gaviscon (extra strength)
1 tablet/dose
100 tablets
$10.49
160 mg Al(OH)3, 105 mg
MgCO3/ tablet
$6.99
1000 mg CaCO3/ tablet