Chapter 13: EDTA Titrations

What is complexation?

Association of two or more chemical species that are capable of independent existence by sharing one or more pairs of electrons

_____ is a Lewis Acid

Metal

_____ is a Lewis Base

Ligand

How are ligands classified?

according to the number of pairs of electrons which they can share with the central metal or metal ion

A ligand that can share one pair of electrons with a metal or metal ion

Monodentate or unidetate

A ligand that can share more than one pair of electrons with a metal or metal ion

multidentate

What determines a metal’s coordination number?

the maximum number of electron pair donor groups that a metal ion can accommodate in complexation reaction

What is chelation?

the process of complex formation where a single central metal ion is bonded to a multidentate ligand

What is a complexometric titration?

a titration based on complex formation

What is the most widely used chelator in analytical chemistry?

ethylenediamine tetraacetic acid (EDTA)

Why use EDTA in titrations?

readily available as a primary standard, forms 1:1 metal-ligand complex, forms stable water soluble metal complexes, and large formation constants with many metal ions

When fully protonated, EDTA is _______

hexaprotic H6Y2+

When electrically neutral, EDTA is ______

tetraprotic, H4Y

The form of EDTA most commonly used in titrations is…

Na2H2Y

What does the formation constant Kf measure?

the extent of formation of the complex at equilibrium

How are metal ligand bond strength and complex stability related?

the stronger the metal ligand bond strength the more stable the complex is

What is a auxiliary complexing agent or masking agent?

a species used to stabilize another species (metal) and keep that other species in solution

What is a colorimetric indicator?

intensely colored substances in at least one form (bound or unbound to the metal) and change color when the metal-ion analyze binds with EDTA