Does Alka-Seltzer Tell the Truth? A lab activity with a video pre-lab assigment

text over students at lab bench: Does Alka-Seltzer Tell the Truth? Asynchronous Video Pre-Lab Assignment

 are a fantastic way to streamline chemistry labs. An effective video pre-lab assignment includes background theory, procedure and technique demonstrations, and sample calculations. After completing such an assignment, students enter the lab more confidently and prepared to carry out the lab procedure safely.

The lab activity shared here is a simple experiment where students use stoichiometric principles to experimentally determine the amount of sodium bicarbonate in an Alka-Seltzer tablet. Novice students tend to find stoichiometric calculations difficult, so practicing the calculations on a pre-lab assignment boosts their confidence and ultimately leads to more successful labs. The Asynchronous Video Pre-Lab Assignment shared here demonstrates the procedure and the calculations required in the experiment.

Video 1: Chemistry Experiment: Does Alka-Seltzer Tell the Truth?, The Science Classroom YouTube Channel, published November 29, 2020.

Procedure time: 
70 minutes
Prep time: 
20 minutes
  • Effervescent tablet
  • Vinegar
  • 250-mL Erlenmeyer flask
  • Electronic balance
  • Weighing paper
  • 100-mL graduated cylinder

Students should complete the Asynchronous Video Pre-Lab Assignment before the lab experiment.

The lab experiment procedure is as follows:

  1. Use the graduated cylinder to measure 35 mL of vinegar and pour it into the 250-mL Erlenmeyer flask.
  2. Place the flask with vinegar on the balance and record the mass in table 1.
  3. Remove the flask from the balance and place it on the lab bench.
  4. Place the piece of weighing paper on the balance and zero (tare) the balance. Put the tablet on the weighing paper and record the mass in table 1.
  5. Add the mass from step 2 and step 4 and record in table 1 as the Mass of vinegar, flask, and tablet - before reaction (g).
  6. Carefully drop the tablet into the vinegar and allow the reaction to go to completion (once the bubbling stops completely, the reaction is over). It may take 5 - 10 minutes for the reaction to complete. Carefully swirl the flask to speed up the reaction. DO NOT SPILL ANY SOLUTION -- If solution spills, the trial needs to be repeated.
  7. When all bubbling has stopped, place the flask on the balance and record the mass in table 1 as the mass after reaction. 
  8. Pour the solution down the drain and rinse the flask with tap water. 
  9. Dry the flask with paper towels for use in the next trial.
  10. Subtract the mass after the reaction from the mass before the reaction and record in table 1 as the mass of CO2
  11. Repeat steps 1 - 9 with a second tablet.
  12. OPTIONAL -- If time allows, repeat steps 1 - 9 with a third tablet.

The Pre-Lab asisgnment does not require any teacher preparation time.

The lab experiment requires about 10 - 20 minutes to gather materials and set them out at the lab benches.


YouTube Video in the Pre-Lab Assignment: housed on



General Safety

For Laboratory Work: Please refer to the ACS .  

For Demonstrations: Please refer to the ACS Division of Chemical Education .

Other Safety resources

: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies



Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at  and further resources at .


Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Assessment Boundary:

Assessment does not include complex chemical reactions.


Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.