Strength Of A Shell Lab

In the Shells lab, we were to test the effect of pH on shell strength. The independent variable in this experiment is the type of liquid that we put the shell in and the independent variable is the shells’ strength. The first thing we did was get our materials and label the two shells. The shell that was going into the vinegar was labeled “E” (which stands for experimental) and the shell that was going to be put in the salt water was labeled “C” (which stands for control since it is the control of our experiment). Before we put them into the water/vinegar, we recorded some quantitative and qualitative observations such as the mass and color and shape of the shells. Then we took the two beakers and poured the 150mL of salt water or vinegar into them and labeled them according to which liquid was inside the beaker.
We then gently set the shells into the liquid making sure not to drop them in and started the timer for thirty minutes. We put shell E in the vinegar since it was our experimental and shell C into the saltwater since it was our control. We then observed them at the 15 minute mark and the 30 minute mark. We didn’t measure mass in the 15 minute mark but instead made qualitative observations about the shells. After 30 minutes, we took the shells out with tweezers, poured out the liquid that was trapped in them and then measured their new masses and recorded other visual observations such as discoloration and change in shape. We then decided that we would test their strength by dropping a textbook on them. We used the same textbook for each shell and had it at the same height when