Part 2: Determining Percent-By-Mass NaHCO3 in Alka-Seltzer
In this part of the lab, the sodium bicarbonate will be the limiting reactant in only some of the trials.
1. Take seven 50 mL beakers from the Containers shelf and place them on the workbench. You should label each beaker by double-clicking on the container. Label each with a beaker number (#1-7).
2. Take a balance from the Instruments shelf and place it on the workbench.
3. Weigh each beaker and record its mass. Note: In a classroom laboratory, the beakers will not all have the same mass. It is therefore important to weigh each beaker independently.
4. The Materials shelf contains a bottle of vinegar solution that is 5% acetic acid. This bottle is labeled "5% vinegar". Take water and 5% vinegar from the Materials shelf and measure the amount of each liquid and solution as specified in the following table into the corresponding beaker:
Beaker Water (mL) 5% Vinegar (mL)
1 30 0
2 28 2
3 26 4
4 24 6
5 22 8
6 20 10
7 18 12
5. Weigh each beaker again after the addition of the water and 5% vinegar. Record the mass of each. Add a 4th column in your table to include the mass of each beaker containing the water and vinegar.
Note: This is not the full initial mass, but the Alka-Seltzer reacts too quickly to measure it with the balance. To find the total initial mass, you will have to add the mass of Alka-Seltzer to this mass. Add a 5th new column in your table to include the total initial mass.
6. Take another 50 mL beaker from the Containers shelf. Place this beaker on the balance, and zero the balance by clicking the Zero button to tare the mass of the beaker.
7. The approximate weight of one tablet of Alka-Seltzer is 3 g. Add 3.000 g Alka-Seltzer from the Materials shelf to the beaker on the balance, and record the actual mass dispensed by reading the balance display. Transfer this Alka-Seltzer to Beaker 1. Wait until all of the bubbling stops. This indicates that the reaction has finished and all gas produced has been released. Repeat this process for Beakers 2-7.
8. Weigh Beakers 1-7 again and record the total mass of each in your Lab Notes. This is the final mass.
9. Clear the bench of all materials, containers, and instruments, then return to your course page to complete any assignments for this lab.
When You Finish Your Experiments:
When you are ready, close the browser window that contains the lab simulation. Go to the Canvas to complete the Lab Quiz and Lab Assignment. The assignment is a Word Document that you should download, complete, and then upload in the Lab Assignment page in Canvas. Your external Lab Notes (in MS Word or pdf) should be uploaded.