complex formation equilibria Flashcards
assemblies of a central metal ion bounded to a group of surrounding molecule or ions
metal complexes
molecules or ions surrounding a complex
ligand
ligand in latin and meaning
ligare = to bind
either an anion or polar molecule
ligand
contain at least one unshared pair of valence electron
ligand
what is the bond called when the central metal ion and the ligand bond
coordinate covalent bond
what is the number of atoms directly bonded to the central atom called
coordination number
contains only a lone pair hence it can donate only one electron pair per ligand
monodentate ligand
possess only single donor atom per molecule and are able to occupy only one site in a coordination sphere
monodentate ligand
example of monodentate ligand
NH3
ligands that contain two or more atoms that can simultaneously coordinate to a central metal ions so they can occupy two or more coordination sphere
polydentate ligand
they appear to grasp the metal between two or more donor atoms
chelating agent in polydentate ligand
advantages multidentate ligands over unidentate
complexometric titrations
generally react more completely with cations and thus provide sharper end points
complexometric titrations
ordinarily react with metal ions in a single step process
complexometric titrations
complex formation with unidentate ligands usually involves how many intermediate species
two or more
among the most important and widely used reagent in titrimetry
EDTA
what type of ligand is EDTA?
hexadentate
what type of base is EDTA?
Lewis
how many binding sites does EDTA have
six with fpur negatively charged carboxylate groups and two tertiary amino groups
ratio of EDTA and all metals
1:1 stoichiometry
is EDTA a base or an acid
EDTA is a weak acid that dissociates in water
which group EDTA dissociates in the 1st and 2nd dissociation
carboxylic group
which group EDTA dissociates in the 3rd and 4th dissociation
amine group
what is the indicator for EDTA or complexation titrations
organic dyes known as matallochromic indicators that form stable complexes with metal ions
if the indicator’s color is red, blue, and orange
red: below 8 pH, blue: 7-11 pH, orange: above 12 pH
what are the metallochromic indicators
- calmagite (8.5-11 pH)
- eriochrome Black T (7.5-10.5 pH)
- eriochrome Blue Black T (8-12 pH)
- murexide (6-13 pH)
- PAN (2-11 pH)
- salicylic acid (2-3 pH)
why is the concentration of auxiliary complexing reagents should always be the minimum
required to prevent precipitation of the analyte
what happens if there is a presence of ammonia
decreases the change in pZn near the equivalence point
titration techniques
- direct titration
- back titration
- displacement titration
- indirect titration
in this titration you simply add an indicator to a buffered solution of the metal ion and titrate with standard EDTA
direct titration
in this titration, an excess of EDTA is added to the metal ion solution and the excess EDTA is titrated with a known concentration of a second metal ion
back titration
why is the second metal ion in back titration must form a weaker complex with EDTA
to avoid displacement of analyte ion
when are back titration used?
- the metal ion blocks the indicator
- when the metal-EDTA complex forms too slowly
- when the metal precipitates in the absence of EDTA
this is used for metal ions that do not have a good indicator
displacement titration
the analyte is treated with an excess of a second metal bound to EDTA and the displaced second metal is titrated with EDTA
displacement titration
EDTA can be used as a titrant for anions like SO4²-
indirect titration
SO4²- is precipitated with Ba as insoluble BaSO4, the precipitate is wash then boil in excess EDTA to complex all the Ba²+, excess EDTA is then back titrated to determine how much Ba is present SO4²-
indirect titration
auxiliary complexing agents can be added to keep metal ions in solution
masking
CN-(cyanide) will form strong complexes with what?
Zn²+, Hg²+, Co²+, Cu+, Ag+, Ni²+, Pd²+, Pt²+, Fe²+, and Fe³+ but not Mg²+, Ca²+, Mn²+, Pb²+
