Titration

Question 1

Ligand

Answer 1

• All ligands are lone pair donors. In other words, all ligands function as Lewis bases.
• binds to a central metal atom to form a coordination complex

Question 2

Monodentate ligand

Answer 2

• Donate to metal ion at one point
• useless in pharmaceutical analysis
• ie, water, ammonia and chloro ligands

Question 3

Bidentate ligand

Answer 3

• Bidentate ligands have two lone pairs, both of which can bond to the central metal ion.
• Like a pair of headphones, carrying lone pairs on each of the “ear pieces”. These will then fit snuggly around a metal ion.

Question 4

Bidentate ligand example

Answer 4

• Structure of ethylenediamine
• aka 1,2-diaminoethane

Question 5

Multidentate ligand/Polydentate ligand

Answer 5

• In pharmaceutical analysis, multidentate ligands are more important
• Donates to metal through more than one point

Question 6

Hexadenate ligand

Answer 6

• A hexadentate ligand has 6 lone pairs of electrons
• all of which can form co-ordinate bonds with the same metal ion.

Question 7

Hexadentate ligand example

Answer 7

• common example:EDTA
• Stands for Ethylenediaminetetracetic acid (EDTA)
• It’s a derivative of etyhlenediamine
• EDTA is used as a negative ion - EDTA4-.

Question 8

Chelation

Answer 8

• Greek word=claw
• The formation of rings with multidentate ligands
• It’s very thermodynamically favoured
• Such complexes have excellent stabiliy.
• In diagram, sp3 hybridisatrion with lone pair on N

Question 9

Ethylenediaminetetraacetic acid (EDTA)

Answer 9

• Chelating agent used in determination of metal ions
• It can be haxadentate, wrapping itself around the metal ion
• When complexing, EDTA can react in its fully ionised form, EDTA^4-
• It’s rarely used fully ionised it’s often complexes metal ions with fewer than 6 co-ordination bonds

Question 10

EDTA in pharmaceutical analysis

Answer 10

Is often used as its disodium salt, Na₂H₂Y

Only four sites available for complexation