Chapter 15: complexation and precipitation reactions and titrations

Ligand

A species that contains one or more electron pair donor groups that tend to form bonds with metal ions

Chelate

A cyclic complex consisting of a metal ion and a reagent that contains two or more electron donor groups located in such a position that they can bond with metal ion to form heterocyclic ring structures.

Tetradentate chelating agent

A molecule that contains four pairs of donor electrons located in such positions that they can bond to a metal ion and form two rings

Adsorption indicator

An organic compound that adsorbs onto the surface of solid in a precipitation, titration. Adsorption or desorption of indicator occurs near equivalence point and thus results in a color change and a transfer of color from the solution to the solid or vice versa.

Argentometric titration

Titration based on formation of precipitates with standard solution of silver nitrate. An example is the titration of a halide ion with silver nitrate to form insoluble silver halide.

Conditional formation constant

An equilibrium constant for the reaction between a metal ion and a complexing agent that applies only when the pH and or concentration of other complexing ions are carefully specified

EDTA displacement titration

An unmeasured excess of solution containing the magnesium or zinc complex of EDTA is introduced into solution of an analyte that forms a more stable complex than that of magnesium or zinc. The liberated magnesium or zinc ions are then titrated with standard solution of EDTA. Displacement titrations are used for determination of cations for which no good indicator exist.

Lewis base

Electron pair acceptor

Lewis acid

Electron pair donor

Water hardness

Concentration of calcium carbonate that is equivalent to the total concentration of all multivalent metal carbonates in water

They form more stable complexes and often form a single complex with a cation

Why are multidentate ligands preferable to unidentate ligands in complexometric titrations?

Overall formation constant beta(n) is equal to the product of the individual stepwise constants

How are step wise and overall formation constants related

Unidentate

Ligands that have a single donor group

Bidentate

Ligands that have two groups available for covalent bonding

Titrant

Generally, ligands acts as the - in complexation titrations

Analyte

Metal ions mostly act as the - in complexation titrantions

Aminocarboxylic acids

What type of acids are used in applications for volumetric determination of most of the metals in the periodic table?

6

How many binding sites does EDTA have?

Back-titrations

What type of titration is useful for determining the cations that form stable EDTA complexes