Honors Chemistry
Name:_____________________________
The Stoichiometry of Alka-Seltzer
This lab will count as your Honors Project. You will submit a typed, formal lab report, including all prelab and post-lab assignments. It will count as a formal grade worth 100 points.
Alka-Seltzer is one of the world’s best-known antacids. Its main function is to absorb excess stomach
acid (HCl). The two main ingredients that accomplish this are sodium bicarbonate (NaHCO3) and citric
acid (C6H8O7). Aspirin is also present in Alka-Seltzer tablets to reduce fever and relieve headaches, but
in this lab, we are going to study the reaction that takes place between the NaHCO 3 and C6H8O7. You
will be doing 2 trials so that you can show precision and accuracy.
Pre-Lab Assignment:
1) Title of Lab
2) Purpose of Lab
3) Balanced Chemical Equation
4) Determine the number of grams of CO2 that will be produced if all 1916 mg of NaHCO3 reacts.
5) Determine the number of grams of CO2 that will be produced if all 1000. mg of C6H8O7 reacts.
*Determine which is the limiting reactant and theoretical yield of CO2 (in grams)
6) Data Table for 2 trials (most important part of pre-lab! You must carefully read through the
procedure to determine what measurements you need to make!)
7) Post Lab Questions with space to answer
Equation:
NaHCO3 (aq) + C6H8O7 (aq)  H2O (l) + CO2 (g) + Na3C6H5O7 (aq)
Objective: Determine what mass of carbon dioxide is produced from the reaction of one tablet of AlkaSeltzer and water. Determine which reactant, NaHCO3 or C6H8O7, is the limiting reactant.
Data: Each tablet contains the following:
1000. mg of C6H8O7
1916 mg of NaHCO3
Procedure:
1) Label and mass two 250 mL beakers for the two trials.
2) Add 100 mL of water to each 250 mL beaker and mass.
3) Determine the mass of one Alka-Seltzer tablet.
4) Add the tablet to the water and observe the reaction. Record your observations.
5) After the tablet has completely dissolved, find the mass of the beaker and its contents.
6) Tap the sides of the beaker to dislodge any bubbles, wait about 10 minutes, and weigh again.
7) Cover each beaker with a watch glass. Heat the beakers to boil off the water until the beaker and its
contents are dry.
8) Determine the mass when cool.
Post – Lab Questions: Show work for all calculations.
1) How many grams of the excess reactant is there in an Alka-Seltzer tablet?
2) How many grams of the limiting reactant would you have to add to your cup after the reaction
is complete to completely use up the rest of the excess reactant?
3) Using your data, what was the percent yield of CO2 in this reaction?
4) Discuss reasons for why your percent yield of CO2 was not 100%. Discuss potential errors that
occurred.
5) Calculate the grams of sodium citrate produced and the percent yield of sodium citrate.
6) Was your percent yield of sodium citrate more than or less than 100%? Explain your results.
7) How many liters of CO2 were produced at the room conditions? Use the Ideal gas law.
8) If you ran this reaction at STP, how many liters of CO2 would have been produced instead?
9) Using the concepts you have learned (including the kinetic molecular theory), explain why #6
and #7 give you a different answer.