CaCO3, one of the most important ingredients in anti-acid pills, is used to effectively remove acid from stomach. CaCO3 is a common ingredient, because neither CaCO3, nor its products with HCl are harmful to the human body. Such a reaction occurs, as follows: CaCO3 (s) + 2 H3O+ (aq) ---> Ca^(2+) (g) + CO2 (g) + 3 H2O (l). This reaction is used to determine the CaCO3 content of a given anti-acid pill. However, since CaCO3 is not water soluble, it can not be directly titrated. The sample must be reacted with an excess amount of HCl solution with known concentration, in order to determine how much HCl is left after the acid reacted with the CaCO3 that was present in the sample.
After the amount of excess HCl has been determined, a normal titration can be performed. During a titration, an indicator produces a visual signal when one reactant has been completely used up (when the equivalence point has been reached). At this point, the number of moles of the other reactant can be determined by using the volume, molarity, and stoichiometric ratio. During this lab, this technique is used to standardize a solution of sodium hydroxide, and thus accurately determine the molarity of the solution. Although indicators are used in this lab, in order to avoid subjectivity, a pH sensor will be used to detect the equivalence point. The sensor monitors the pH as the titrant solution is added, and thus the steepest point of the curve represents the equivalence point.
To determine the CaCO3-content of a anti-acid pill and compare with the nominal value of a generic.