The outer shells of two eggs are removed. One is kept in water and the other in dil. HCl. What will one observe? Why?
The egg shell placed in the water will produce no noticeable observation. Water has a pH of 7, which places it in a neutral position on the pH scale. Water will tend to hold onto it's hydrogen ions and therefore offer no available potential to produce a chemical change.
Dilute hydrochloric acid, on the other hand, is a weak acid, somewhere in the vicinity of 4 to 6 on the pH scale. This means it will dissociate into hydrogen ions (H+) and chlorine ions (Cl-). The egg shell has a high concentration of calcium, which will combine in solution with the chlorine ions to form calcium chloride, a salt. The shell will noticeably dissolve, leaving behind the cell membrane, a rubbery, pliable substance that once served to house the interior of the egg.