Edta Titration: Determination of Mg2+

Topics: Titration, PH indicator, Erlenmeyer flask Pages: 4 (1264 words) Published: April 10, 2013
The objective of this experiment is to utilize the techniques of weighing and titrating to determine the total amount of MgSO4 present in an unknown sample. Standardized EDTA will be used to titrate the unknown solution. This type of reaction is a complexation reaction, which usually involves Lewis acids and bases. EDTA in complexation reactions serves as a chelating ligand. The base, EDTA, will bind to the metal ions, which serve as the Lewis acid, thus playing a role as a ligand. The indicators used in EDTA titrations are metal ion indicators. Metal ion indicators work by the presence of absence of metal ions. Just like EDTA, the metal ion indicators will bind with metals. When the titrations begin, Mg2+ will be formed in a complex with the indicator. Once EDTA is added, it binds to the free Mg2+ ions, and then it reacts with the Mg2+ ions that are already bound to the indicator. When the EDTA is added, the solution will turn red. Once the solution turns from red to blue, that is the end point of the titration. The color change marks when the indicator is not bonded to the metal ion. The indicator used is “Eriochrom Black T”. If the proper techniques of weighing and titrating are employed in this experiment, the percentage of MgSO4 present in the unknown sample for each trial should be similar and precise.

The concentration of the standardized EDTA solution was obtained from the TA. A clean and dry weighing bottle was used to obtain the unknown. After obtaining the unknown, it was placed in a desiccator until titrating began. A 250 mL beaker was used to obtain the EDTA solution. A buret was acquired and rinsed with deionized water. After rinsing with deionized water, the buret was then rinsed with 5-10 mL of the standardized EDTA solution. The standardized EDTA solution was then used to fill the buret. 0.14 to 0.16 g of the unknown sample was weighed out by using the weigh-by-difference technique and placed in a 250 mL...
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