Chemistry Lab 114 – R5Determination of Copper (Cu2+) by TitrationPurposeThe purpose of this experiment is to use a special type of titration known as a complexometrictitration in order to determine the mass percentage of copper in the unknown solution. In theexperiment, a strongly bonding Lewis base, also known as the complexing reagent, is attached tothe copper cation forming a copper complex. The endpoint of the titration is reached whenenough of the reagent has been added to complex all of the metal ions in solution.TheoryThe theory behind this experiment is to utilize the complexing ability of the complexing reagent,known as ethylenediaminetetraaceticacid (H4EDTA), to bind all of the metal ions in the unknownsolution in order to determine the mass of copper in the unknown solution and the correspondingmass percentage of copper. Due to buffering, it is actually the anion of the acid, EDTA4-, thatcomplexes to the metal ions. EDTA4-reacts with the metal by forming coordinate-covalentbonds. The resulting structure is a coordination compound, or complex. Ligands such as EDTA4-that can form more than one of these coordinate-covalent bonds are called chelates. A total of sixcoordinate-covalent bonds are formed between the copper cation and EDTA4-. When thebuffering solutions (NH4Cl and NH4OH) are added to the unknown copper solution, the colorchanges from light blue to dark blue. When the Murexide indicator solution is added, the solutionturns an even darker violet color. Depending on the sample, the color may be gray or blue tinged.As the EDTA4solution is titrated into the copper solution and swirled constantly, the solution willgradually turn yellow. The color change from yellow back to pale violet indicates the endpoint.