Removal of Calcium and Magnesium Salts from Water

One of the most important factors determining water quality is its degree of hardness. The water hardness level depends on the concentration of calcium and magnesium ions it contains.

During hardness analysis, Ca and Mg are not differentiated. Therefore, hardness is determined in terms of CaCO3.

In our daily lives, we can better observe water hardness when washing laundry with soap or when bathing in a bathtub rather than a shower. This is because Ca+2 and Mg+2 ions form insoluble salts with the raw materials in soap.

To determine water hardness, a chelating agent that can easily chelate with Calcium and Magnesium ions is necessary.

Ethylenediaminetetraacetic acid(EDTA) is the best chelating agent used for determining water hardness. Due to its structural properties, it is a weak acid that can achieve complete neutralization by losing 4 protons in water.

EDTA's Factors Affecting the Chelating Property?

As can be seen from EDTA's molecular structure above, the four acid molecules at the terminal ends and the two nitrogen atoms all contain unshared electron pairs. Consequently, a single EDTA molecule has the ability to form a complex with one cation at each of its six sites.

How is the Chelated Complex Formed?

When EDTA is added to hard water, all of the Calcium and Magnesium ions in the water will form a chelated complex. During this process, all the ions can be converted into the complex form.

In the structure of EDTA's metal complexes, the EDTA anion can act as a tetra-, penta-, or hexadentate chelating agent with the metal being complexed.