Exp. 10:
Antiacid Analysis
Required Locker Materials:
- Gas apparatus (see figure)
- Small vial
- Standard test tube
Safety:
- Eyewear MUST be worn at all times
Waste:
- All liquid waste must be disposed in the
waste containers.
Experimental Objective:
The object of the lab is to determine the percentage of active anti-acid compound in a
commercially available antiacid medication. Experimentally this will be done by using a gas
collection apparatus to collect the carbon dioxide produced in the reaction of the antiacids
with hydrochloric acid.
Students will again learn to combine a stoichiometry problem with a gas law problem. In
addition, students will also deal with vapor pressures and partial pressure when doing the
calculations.
Introduction:
Many commercial, over-the –counter antacids contain either a carbonate or a bicarbonate
(i.e., hydrogen carbonate) compound as the active ingredient. For example, Alka Seltzer®
contains NaHCO3 and Tums® contains CaCO3. When these antacids reach the stomach, the
following reaction with gastric juice (which is mostly 0.2 M HCl) occurs:
Alka Seltzer: NaHCO3 + HCl 
Tums:
CaCO3 + 2HCl
NaCl + H2O + CO2
 CaCl2 + H2O + CO2
Procedure
For this experiment record all observations and
measurements in your notebook:
1. Obtain about 200 mL to tap water in a beaker and
mix in about 5 mL of 3 M HCl.
2. Dissolve approximately 1.0 g of NaHCO3 (watch
out for fizzing overflow). This will saturate the
mixture with CO2.
3. Use the solution to fill a leveling bulb/buret
assembly as shown in Figure 10-1, except raise
the leveling bulb higher. Set the water level in the
buret near the 5 mL mark.
4. Obtain 25 mL of 3 M HCl. Dissolve 0.2 g of
NaHCO3 in order to saturate it with CO2. (Keep
this solution stoppered when not in use).
5. Measure about 5 mL of this solution into a
medium-sized test tube, and position it next to the
gas buret assemble.
Exp. 10:
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Leo Truttmann – Fall 13
6. Without touching the tablet directly, break an antacid tablet (note the brand) into small
pieces and accurately weigh (to the nearest ±1mg)a sample in the range 0.2 to 0.3
grams, placing the sample inside a small vial.
7. Carefully, nest the vial inside the test tube containing the CO2-saturated HCl solution.
8. Stopper the rest tube, re-equilibrate the water levels in the leveling bulb and buret near
the 5ml mark, if necessary, and record the initial volume in the buret (±0.1 mL).
9. To initiate the reaction, tilt the test tubes so that the contents mix efficiently.
10. When the fizzing reaction has subsided, re-align the leveling bulb until the water levels
are at same pressure. Tap the test tube to dislodge any bubbles, then equilibrate the
water levels and record the final volume (± 0.1 mL).
11. Calculate the volume difference as VCO2 produced from the tablet.
12. Record the barometric pressure (Pair) and room temperature (assume it is the same as
the temperature of the CO2 being collected).
13. Repeat the experiment twice more with accurately-weighed pieces of the tablet. (reset
the water level near the 5 ml mark when restarting the experiment.)
Calculations
For the calculation start a new section in your notebook. Remember you need to show
every calculation you do by writing down the equation and an example calculation. The
example calculation only needs to be done for one trial. The results of the remaining trials
can be written down in a table in your notebook.
For the next Lab meeting organize all your data and calculations in an excel table which is
due at the beginning of the Lab.
Volume of carbon dioxide
The volume of carbon dioxide is the difference between your initial and final volume reading
with your gas buret.
Vapor pressure of water
The vapor pressure of water only depends on the temperature. Read the vapor pressure
from a table based on the measured room temperature. Make sure you write down the
correct unit.
Partial pressure of carbon dioxide
The pressure of carbon dioxide in your apparatus is less than the atmospheric pressure in
the lab. The difference is that nitrogen was collected over water which exerts a small
pressure called vapor pressure.
Moles of carbon dioxide
With the ideal gas equation the number of moles of carbon dioxide can be calculated.
Mass of NaHCO3 or CaCO3
With the number of moles known, the mass can be calculated by using the molar mass of
the corresponding compound.
% of NaHCO3 or CaCO3 in original tablet
Calculate the percentage of the active ingredient in the initially measured tablet.
Exp. 10:
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Leo Truttmann – Fall 13
Average % and Average Deviation of the % mass
Calculate the average mass percentage of your trial and the average Deviation.
Measurements
Trial 1
Mass of tablet
[g]
Mass sodium nitrite
[ml]
Volume initial
[ml]
Volume final
[ml]
Temperature
[C]
Barometric pressure
[mmHg]
Exp. 10:
Page 3 of 3
Trial 2
Leo Truttmann – Fall 13
Trial 3