Science Buddies: "Ask an Expert"

Hi, I am considering to do an experiment with bath bombs. I am planning to investigate the concentration of baking soda (NaHCO3) in bath bombs at lush (using titration?). But I am not sure how this will work. Do you guys have any suggestions to help?
Thanks!

Hello paulanders0623,

If you want to determine the amount of some substance in a bath bomb, I might suggest this fun idea:

The active ingredient that you may be interested in is the cause of the 'fizz.'

One way to quantify the amount of the reagent responsible for this fizz is to capture the evolved gas (CO2). Invert a graduated cylinder or beaker or measuring cup or other container while under water and lift above the water's surface. (Same idea as putting your thumb over a straw and pulling up the liquid.) Put a bath bomb (or carefully measured piece of the bath bomb) under this inverted container. You'll capture the evolved gas and be able to measure the volume of the evolved gas.

From this volume, you can determine how much CO2 was released using an the ideal gas law. You can then convert the mass or moles of CO2 to the active ingredients if you know the chemical reaction, e.g.

C5H7O5CO2H (aq.) + NaHCO3 (aq.) → C5H7O5CO2−Na+(aq.) + H2O(l) + CO2 (g)

where there's 1 mole of NaHCO3 for every mole of CO2.

-John