Determination of Water Hardness Through the Titration of Standard Solution of Ethylenediamminetetraacetic Acid (Edta)
Introduction Why: The goal of this experiment is to determine the water hardness of the prepared unknown water sample. Determining water hardness is a useful test that measures the quality of water for its household and industrial users. Water’s hardness arises from the presence of metal ions – specifically metal ions with a charge of +2 or higher. The ‘scum’ left over in a cleaned shower stall or coffee pot is equivalent to water hardness. Water dissolves salts which contains ions of sodium, magnesium, calcium, iron, and many other metal; however, the most prevalent ion found is calcium. Since calcium ions typically make the most predominant contribution to water hardness, by convention hardness is reported as mg 〖CaCo〗_3/L of solution. Water with a hardness value less than 60 ppm is considered “soft” water, while water ≥ 200 ppm 〖CaCo〗_3/L is labeled as “hard”.
How: Ethylenediamminetetraacetic Acid (EDTA) is a complex versatile chelating agent. A chelating agent is a substance whose atoms can form several bonds (ligands) to a single metal ion. Chelating agents are multi-dentate ligands. Multidentate ligands are many clawed, holding onto the metal ion to form a very stable complex. EDTA can form four or six bonds with a metal ion. EDTA is used to capture and bind the metal ions. However, EDTA and the EDTA-complex are both colorless compounds and so an indicator will also need to be used. In order to prepare for titration, 500 mL of approximately 0.004 M disodium EDTA solution is created by weighing 0.7761 grams of 〖Na〗_2 EDTA dissolved in approximately 500 mL of deionized water. The stock calcium ion and the prepared unknown water sample, Unknown # 7 are used to standardize the 〖Na〗_2 EDTA solution.
The indicator for this experiment is called Eriochrome Black T. It will show complete EDTA chelation of the metal impurities by a color change from pink to blue. Blue represents that the H_2 〖In〗^- (In stands for indicator) anion is free of calcium ions. Further
How: Ethylenediamminetetraacetic Acid (EDTA) is a complex versatile chelating agent. A chelating agent is a substance whose atoms can form several bonds (ligands) to a single metal ion. Chelating agents are multi-dentate ligands. Multidentate ligands are many clawed, holding onto the metal ion to form a very stable complex. EDTA can form four or six bonds with a metal ion. EDTA is used to capture and bind the metal ions. However, EDTA and the EDTA-complex are both colorless compounds and so an indicator will also need to be used. In order to prepare for titration, 500 mL of approximately 0.004 M disodium EDTA solution is created by weighing 0.7761 grams of 〖Na〗_2 EDTA dissolved in approximately 500 mL of deionized water. The stock calcium ion and the prepared unknown water sample, Unknown # 7 are used to standardize the 〖Na〗_2 EDTA solution.
The indicator for this experiment is called Eriochrome Black T. It will show complete EDTA chelation of the metal impurities by a color change from pink to blue. Blue represents that the H_2 〖In〗^- (In stands for indicator) anion is free of calcium ions. Further