Determination of amount of NaHCO3 in Alka Seltzer Tablets

Objective : Determine the amount of NaHCO3 in Alka Seltzer tablets using stoichiometry.: Make sure this is handwritten in the lab notebook.

Use the “LAB : HOW TO…” link from the class website if you need help with how to use balance, Bunsen burner… and such.

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Procedure :

Alka Seltzer is an effervescent tablet containing aspirin (acetylsalicylic acid), citric acid, and NaHCO3. Vinegar is 5% acetic acid aqueous solution.

(1)Add 35mL of water (use 50mL/100mL graduated cylinder) to a container #1.

(2)Measure the mass of container and its content.

  • What is that a mass of?

(3) Measure the mass of one Alka Seltzer tablet.

  • How would you know if all the ingredients or just the active ingredients are written on the package?

** Record the content and amount of Alka Seltzer tablet ingredients from the package.

(4)Drop the tablet into the container and mix carefully. As soon as the bubbling stops, measure its mass.

  • What is that a mass of?

(5)Fill container #2 with 5mL vinegar and 30mL water. Repeat (2), (3) & (4).

  • what is the total volume?

(6) Fill container #3 with 10mL vinegar and 25mL water. Repeat (2), (3) & (4).

(7) Fill container #4 with 15mL vinegar and 20mL water. Repeat (2), (3) & (4).

(8) Fill container#5 with 20mL vinegar and 15mL water. Repeat (2), (3) & (4).

(9) Fill container#6 with 25mL vinegar and 10mL water. Repeat (2), (3) & (4)

(10)Fill container #7 with 30mL vinegar and 5mL water. Repeat (2), (3) & (4).

(11) Fill container #8 with 35mL vinegar. Repeat (2), (3) & (4).

  • Which solution is most acidic? Explain.

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Prelab Questions :Make sure the Q and A’s are all hand written for this part!

Alka Seltzer is an effervescent tablet containing aspirin (acetylsalicylic acid), citric acid, and NaHCO3.

NaHCO3(s) + H+ (aq)  Na+(aq) + H2O (l) + CO2 (g)

(PL1) In order for this reaction to occur, you need both reactants. NaHCO3(s) comes from the Alka Seltzer tablet. Where does H+ come from in solution 1?

(PL2) What would be the visual indication that the reaction did occur?

(PL3) If NaHCO3(s) is the limiting reactant, what happened to the amount of CO2 produced when more H+ is added?

(PL4) If H+ (aq) is the limiting reactant, what happened to the amount of CO2 produced when more H+ is added?

(PL5 ) Calculate the amount of NaHCO3 associated when a reaction generated 5.078g of CO2. Show your work clearly.

(PL6) Is the answer to (PL5) the amount of NaHCO3present in the tablet or the amount of NaHCO3reacted ?

(PL7) Fill in the blank. ( Pick from < , > , =, , )

The amount of NaHCO3 present in the tablet ___ amount of NaHCO3 reacted to produce CO2

(PL8) Draw a data table you will be filling in during the lab. Include all the measurements that will be made in this lab and qualitative observation if needed.

Analysis : : Make sure this is handwritten in the lab notebook.

(A1) Calculate the mass of CO2 generated in each solution.

(A2) Starting from CO2 amounts, calculate mass ofreacted NaHCO3 in the tablet for each experiment. Show your work at least once clearly.

(A3) Draw the amount of reacted NaHCO3 (y-axis) vs. the volume of vinegar used. Draw the best fitted line/curve. Make sure your data points are still clear.

(A4) Figure out the amount of NaHCO3 present in one tablet. – This may not be a calculation question.

Question :Make sure the Q and A’s are all hand written for this part!

(Q1) Compare the experimental (yours) mass of NaHCO3(s) to theoretical (from the package) mass of NaHCO3(s). Give two reasons why they might be different.

(Q2) What is the relationship (directly, inversely, or not related) between the amount of acid (H+) in the beaker and the amount of CO2 generated?

(Q3) If you were to re-design the lab to get more accurate result, what change(s) would you make in the procedure? Briefly explain.

(Q4) Remember how the bottles were sitting on the bottom of the container, would it be a better idea to shake or stir the mixture to pop those bottles or leave them in the mixture when the final mass is measured? Briefly explain.

Summary :: Make sure this is handwritten in the lab notebook.

Everything in the summary should be a ‘repeat’ of what you already have in data or analysis section. You have to have the summary in this given format!

Mass of Alka Seltzer tablet (report all) ______

Mass of CO2 generated(report all) ______

Mass of NaHCO3reacted (report all) ______

Mass of NaHCO3 present (report ONE and explain where this one value is coming from) ______

Theoretical mass of of Alka Seltzer tablet ______
Theoretical mass of NaHCO3in each tablet______

Abstract: : Make sure this is handwritten in the lab notebook.

No more than 100 words stating why the lab was done, what was done, the major result(s), and conclusion(s).

Reflection Statement:: Make sure this is handwritten in the lab notebook.

One thing I might do differently next time is …… because…….