Question

$EDTA$ is hexadentate ligand and is used to remove hardness in water .
A.True
B.False

Answer 1

The donor atoms , molecules or anions which donate a pair of electrons to the metal atom or ion and form a coordinate bond with it are called ligands . They attach with different metal atoms or ions to form complexes .

Complete step by step answer:
Hexadentate ligand is one in which there are six donor atoms .
$EDTA$ is ethylenediaminetetraacetate and its structure is as shown below :
${H_2}C - \ddot N < _{C{H_2}CO{O^{: - }}}^{C{H_2}CO{O^{: - }}} \\\ {H_2}\mathop C\limits^| - \ddot N < _{C{H_2}CO{O^{: - }}}^{C{H_2}CO{O^{: - }}} \\\$
As we can see from the structure that it has six donor atoms , that is , two nitrogen and four oxygen atoms ( of the carboxylic acid groups ) capable of bonding to the metal atom . Hence it is a hexadentate ligand .
As we know that hardness of water is due to presence of calcium and magnesium ions which are metal ions and can form complex ligands .
$EDTA$ is a hexadentate ligand and hence it coordinates through two nitrogen atoms and four oxygen atoms with the metal ion and forms stable complexes .
Since , the metal ions ( $C{a^{2 + }},M{g^{2 + }}$ ) form stable complexes with $EDTA$ , it is used to remove the hardness of water .

Note:
$EDTA$ is the most commonly used hexadentate ligand . A lot of metal ions react completely with this ligand at an appropriate pH to form stable complexes . The disodium salt of ethylene diamine tetraacetate is commonly used because of its better solubility in water .