By Brynne

The purpose of this experiment was to determine which toothpaste most
effectively prevents tooth decay. To carry out this experiment, 21 petri
dishes were filled with 5 ml of Coke. A limestone chip was placed inside each
petri dish and soaked in the Coke for 24 hours. After 24 hours, the
limestone chips were placed onto a balance to record their mass and then
brushed with one of the seven different types of toothpaste that were tested;
three chips were brushed with Crest, three were brushed with Listerine, three
were brushed with Tom,s Natural, three were brushed with Mentadent, three
were brushed with Colgate, three were brushed with Aquafresh, and the other
three were left unbrushed to serve as controls. Each limestone chip was then
returned to its container. This procedure was repeated for 10 days (not
consecutive).
After completing this experiment, the results didn,t answer the question
about toothpaste effectiveness because there were many unexpected chemical
reactions that occurred.
When this experiment was first planned, it was thought that the Hydrogen
from the acid in the soda would break down the CaCO3 ( calcium carbonate),
and the chips would lose mass. What really happened was the soda contained PO4
-3 (phosphate) which when combined with Ca+2 (calcium) on the surface of the
chip, caused the chips to gain mass. Another chemical reaction that occurred
was the Ca+2 (calcium) pulled the H+ (acid) out of the soda and onto the
surface of the chips, thus changing the soda into a basic solution and making
the chip increase in mass. The average percent increase in mass on the chips
was: the control with 22%, Colgate with 22.4%, Crest with 6.93%, Aquafresh
with 8.2%, Tom,s Natural with 9.16%, Listerine with 24.5%, and Mentadent with
9.06%. It can be concluded that in some way the Crest, Mentadent, Tom,s
Natural, and Aquafresh worked better because the Listerine and Colgate were
closest to the control and gained the most mass whereas the Crest, Aquafresh,
Mentadent, and Tom,s Natural didn,t gain as much mass.