Jenny Huh
9/8/11
AP Chemistry
Jacobus Period 6
Inquiry Determination Lab
Conclusion:
Based on experimental results of CO2 production, the amount of H+ present increases the
production of CO2 by an overall 106% due to the increase of acidity from the vinegar solutions. The
percent by mass of the NaHCO3 in each run increases by 102% as the amount of vinegar used in
solution increases.
Analysis:
Alka Seltzer, containing acetylsalicylic acid (HC9H7O4), citric acid (HC6H7O7), and sodium
bicarbonate (NaHCO3), is an antacid and analgesic medication that dissolves when in contact with
water, emitting “bubbles” identical to carbonation. The tablet when dissolved in water undergoes
an acid-base reaction where the sodium bicarbonate reacts with the acetylsalicylic and citric acids,
resulting in the reaction of HCO3- (aq) + H+ (aq) H2O (l) + CO2 (g). The carbon dioxide gas produced
causes the “bubbling” of the tablet and the loss of the CO2 gas results in a difference of mass at the
end of the reaction. By using the mass difference the percent by mass of sodium bicarbonate that
had reacted in the Alka Seltzer tablet can be calculated.
When an Alka Seltzer tablet is dissolved in a water solution the sodium bicarbonate is in
excess and the H+ from the acid is the limiting reagent (reference page 2). Only a portion of sodium
bicarbonate can react due to the limit of H+ in the reaction. When using a vinegar-water solution
instead, more acid is available to the reaction and more sodium bicarbonate is able to react, thus
producing more CO2. With increasing volumes of vinegar more CO2 is produced and eventually the
H+ will become the excess reagent and sodium bicarbonate the limiting reagent. The amount of
sodium bicarbonate in each tablet is the constant 1916 mg so additional CO2 will not be produced
as increasing volumes of vinegar are added to the solution.
Eight runs were performed during this experiment with a consistent volume of 35 mL
solution. The first run, acting as a control, consisted of 35.0 mL of water and 0 mL of vinegar had an
initial mass of 142.47 g and a final mass of 145.05 g. By using the difference of mass the grams of
CO2 lost can be calculated, which was about 0.67 g of CO2 lost in the reaction (reference calculations
on page 5). The second run consisted of 30.0 mL of water and 5.00 mL of vinegar which massed to
143.03 g and a final mass of 145.01 g. The CO2 lost was approximately 0.85 g. The amount of
vinegar used in each run increases by regular increments of 5.0 mL (for rest of runs refer to data
table on page 4). As more vinegar is used there is a larger amount of CO2 being released as the
increase of H+ from the vinegar is available to drive the reaction to completion, being able to
produce more products (CO2). Observation of the trend on the graph (see attached) shows the
amount of CO2 released increases as the amount of vinegar used increases as well. There is a 26.9%
increase of CO2 between Runs 1 and 2 and a 25.4% increase between Runs 1 and 3. There is a
56.7% increase of CO2 between Runs 1 and 4 and a 47.8% increase between Runs 1 and 5. Between
Runs 1 and 6 there is a 53.7% increase, a 55.2% increase between Runs 1 and 7 and a 106%
increase of CO2 between Runs 1 and 8.
The percent by mass of NaHCO3 in each tablet in each run conducted in this experiment
increased as the amount of vinegar used in solution increased as determined through stoichiometry
relationships. Observation of the trend on graph 2 shows a similar trend as the graph of CO2
released compared to the amount of vinegar used. In Run 1, 1.28 g of NaHCO3 was used and the
percent by mass was 39.4%. In Run 2, the NaHCO3 used was 1.62 g and the percent by mass was
50.2%, in Run 3 1.60 g and 49.2%, Run 4 2.00 g and 60.6%, Run 5 1.89 g and 57.6%, Run 6 1.97 g
and 60.4%, Run 7 1.99 g and 60.7%, and Run 8 with 2.63 g used and a percent by mass of 79.7%
(refer to page 5 for calculations).
A source of error in this lab would be if the Alka Seltzer tablet was not fully dissolved before
final massing. If the tablet was massed without fully dissolving then the amount of CO2 released is
lower than the amount if the tablet was fully dissolved, which explains the inconsistency of the
trend of the graph where the increasing volume of vinegar had a lower amount of CO2 lost, for
example between Runs 2 and 3 and between Runs 4 and 5 (reference page 3). Another source of
error in this lab would be the difference in mass of the beakers used. Two different beakers were
accidently used during this experiment and the difference of mass of the beakers would have
affected the results of the lab when massing the initial and final masses of the different runs. Also,
there is a possibility of an inconsistency with 35.0 mL of solution as more or less could have been
used with each run.