DRAFT: This module has unpublished changes.

February 23rd, 2011


Purpose: To determine the CaCO3-content and compare with the nominal value of a generic.


Background: Antacid pills contain CaCO3 which reacts with HCl in the stomach to get rid of excess acid. To perform this experiment, a back titration method needs to be used because CaCO3 is not water soluble. To do this, a known amount of HCl is added to a crushed antacid pill and a titration is used to determined how much HCl was in excess. After doing this, the CaCO3 content of the pill can be determined. A titration is an example of quantitative analysis that determines the unknown concentration of a reactant. Knowing the amount of a substance in a solution allows one to use collected data to learn exactly how many mL of the titrant was needed to reach the equivalence point. The equivalence point is the point at which all of the unknown solution has reacted. By tracking this process on a graph, a clear equivalence point can be observed. This data also allows the experimenter to learn how many moles of the titrant were needed to completely react with the solution of unknown concentration because at the equivalence point the volume and molarity are known. Because chemical reactions always happen in specific stoichiometric ratios, we can then calculate the concentration of the unknown solution by using the formula: C = n/V Where C= concentration (mol/L) n= amount of substance (mol) V= volume of the solution(liters) A common method of performing a titration is with indicators (like phenolphthalein which turns the solution pink). The indicator changes the solution a different color at the equivalence point to show equilibrium has been reached. However, this method is not the best way to perform a titration because it is impossible to determine the exact amount of solution needed and always involves some subjectivity when determining color change. Using an automatic titrator system is an extremely more effective way to conduct a titration. This requires a pH sensor which takes the place of human inference.

DRAFT: This module has unpublished changes.