Determination of Cu2+ by Titration
The purpose of this lab is to determine the concentration of copper ions in an unknown solution. Complexometric titration will be used to determine the concentration. A buret will be used to deliver the complexing agent to the unknown solution. Ethylenediaminetetraacetic acid will be used as the complexing reagent. An indicator, Murexide in our case, will be used to indicate the endpoint of the reaction.
Theories and Concepts:
The anion of the acid, EDTA4-, will complex to the metal. This anion reacts with the metal by forming coordinate-covalent bonds with the metal. This is a coordination compound. This ligand is called a chelate because it can form coordinate-covalent bonds by wrapping itself around the metal. A total of six coordinate covalent bonds are formed between the copper cation and the ligand. The Murexide indicator will mix with the blue copper solution to form a compound that is purple. As soon as an exact amount of the ligand is titrated and binded to all of the metal in the solution the color of the solution will change immediately. The reaction in this lab is Cu2+In + EDTA4- Cu2+ EDTA4- + In.
Measure exactly 25.0 mL of your unknown copper solution into a graduated cylinder and place it in a 250 mL Erlenmeyer flask.
Add 10 mL of 1 M NH4Cl to this it and mix the solution by swirling
Add 5 mL of 1 M NH4¬OH and notice the color change
Add 15 drops of Murexide indicator to the dark blue solution. This will turn the solution to a violet color.
Fill a buret with the standard EDTA4- solution to a point somewhere between the 0 and 2 mL mark and carefully read the initial volume of the buret. Record it.
Record the molarity of the EDTA4- solution.
Slowly titrate the EDTA4- solution into the copper solution.
Swirl constantly, and the solution will gradually turn yellow
Continue titrating and when the...