Part 13 EDTA Titrations

Presentation Transcript

Part 13 EDTA Titrations Lewis corrosive base idea Lewis corrosive : electron match acceptor metal Lewis base : electron combine contributor ligand arrange covalent bond ligand gives both electrons of the electron combine bond

organize covalent bond

Species with at least two cores that are great Lewis bases are potential chelate ligands. The term chelate was initially connected in 1920 by Sir Gilbert T. Morgan and H.D.K. Drew, who expressed: "The descriptor chelate, got from the colossal paw or chela ( Greek: chely) of the lobster or different scavangers, is proposed for the caliper-like gatherings which work as two partner units and secure to the focal molecule to deliver heterocyclic rings." This term is non specific for all ligands which have no less than two particles facilitated to the focal metal particle.

Chelate Effect the capacity of multidentate ligands to frame more steady metal edifices than those shaped by comparative monodentate ligands comes about because of the development of 5-membered "ring" with metal and two particles on the ligand

Metal particle Monodentate Stability 

Metal particle Bidentate Stability 

Metal particle Tridentate Stability 

Metal particle Tetradentate Stability 

What types of EDTA exist? At Low pH? Which Functional Groups will be protonated?

EDTA is a Hexaprotic corrosive (H 6 Y 2+ ) pK 1 = 0.0 ,pK 2 = 1.5 ,pK 3 = 2.0 pK 4 = 2.66 ,pK 5 = 6.16 ,pK 6 = 10.24 The measure of ethylenediaminetetraacetate anion, EDTA - 4 => Y - 4 in arrangement is essential. WHY????

EDTA - 4

[Fe(EDTA)(H 2 O]

Let's investigate the a plot for EDTA

EDTA M +n + Y - 4 ¾ MY (n-4)+ [MY (n-4)+ ] K MY = - [M][Y - 4 ] [Y - 4 ] a 4 = - C T where C T = [Y - 4 ] + [HY - 3 ] + [H 2 Y - 2 ] + [H 3 Y - 1 ] + [H 4 Y]

Minimum pH for Effective EDTA Titrations

Metal Ion Indicators Erichrome Black T MgIn + EDTA  MgEDTA + In (red) (dull) (blue)