Ch 17 Complexation and Precipitation Reactions and Titrations Flashcards
In the formation of complexes, what do you call the donor species that has at least one pair of
unshared electrons available for bond formation
ligand
Common inorganic ligands:
Water, ammonia, and halide ions
is an ion or a molecule that
forms a covalent bond with a cation
or a neutral metal atom by donating a
pair of electrons, which are then shared
by the two
ligand
The number of covalent bonds that a cation tends to form with electron donors
is its
coordination number
Titrations based on complex formation, sometimes called
complexometric titrations
is produced when a metal ion coordinates
with two or more donor groups of a single ligand to form a five- or six-membered
heterocyclic ring
chelate
A ligand that has a single donor group, such as ammonia, is called single-toothed or
unidentate
A ligand that has a two donor group, such as glycine
bidentate
comes from the Latin word
dentatus and means having toothlike
projections
Dentate
Another important type of complex is formed between metal ions and cyclic
organic compounds, known as
macrocycles
macrocyclic compounds that form three
dimensional cavities that can just accommodate appropriately sized metal ions.
cryptands
Are pH-dependent equilibrium constants
that apply at a single pH only. Commonly used when the complex compound formed are pH dependent
conditional formation constant
In these titrations, a
metal ion reacts with a suitable ligand to form a complex, and the equivalence point
is determined by an indicator or an appropriate instrumental method.
complexometric titrations.
Usually in complexometric titrations, the ligand is the ________, and the metal ion is the ______
titrant, analyte
Titration that is based on reactions that yield ionic compounds of limited solubility
Precipitation titrations
Titrations with silver nitrate, the most widely used and important precipitating reagent, are sometimes called
argentometric titrations
titration curves for precipitation reactions is consist of a plot of
pAg (y-axis) vs. volume of the silver reagent (x-axis)
The 3 End Points for Argentometric Titrations
Chemical, potentiometric, and amperometric end points
the potential difference between a silver electrode and
a reference electrode is measured as a function of titrant volume
potentiometric titrations
the current
generated between a pair of silver electrodes is measured and plotted as a function of
titrant volume
amperometric titrations
The ______________is one of the most common argentometric methods. In this method, silver ions are titrated with a standard solution of
thiocyanate ion, where Iron(III) serves as the indicator. The solution turns red with the first slight excess of
thiocyanate ion due to the formation of Fe(SCN)^2+.
Volhard method
An argentometric titration, wherein sodium chromate serves as the indicator of chloride, bromide, and cyanide ions. Silver ions react with chromate to form the brick-red silver chromate (Ag2CrO4)
precipitate in the equivalence-point region.
Mohr method
The ________________ uses an adsorption indicator, an organic compound that
adsorbs onto or desorbs from the surface of the solid in a precipitation titration. Ideally, the adsorption or desorption occurs near the equivalence point and results not
only in a color change but also in the transfer of color from the solution to the solid
or vice versa.
Fajans method
these are the stable complexes, produce by organic complexing agents, that bind a metal and prevent interferences
masking agents
Who recognized tertiary amines that remarkably form stable chelates with many metal ions
Gerold Schwarzenbach
most widely used complexometric titrant
EDTA/ Ethylenediaaminetetraacetic acid
the six potential sites of EDTA for bonding a metal ion:
four carboxyl groups and the two amino groups, each of the latter with an unshared pair
of electrons.
Solutions of EDTA are particularly valuable as titrants because the EDTA combines
with metal ions in a ____ ratio regardless of the charge on the cation.
1:1
EDTA and other similar chelating agents are often called because of their ability to remove or inactivate metal
ions
sequestering
agents
must be used in EDTA titrations to prevent
precipitation of the analyte as a hydrous oxide. Such reagents cause the end points to be less sharp.
auxiliary complexing
agents
a typical metal-ion organic dyes that form colored chelates with metal ions, where the metal complexes form are generally red. It behaves as an acid/base indicator as well as a metal-ion indicator for EDTA Titrations.
Eriochrome Black T
What are the Titration Methods Involving EDTA
Direct Titration:
Methods Based on Indicators for the Analyte.
Methods Based on Indicators for an Added Metal Ion.
Potentiometric Methods.
Spectrophotometric Methods
Back Titration:
Displacement Methods
In ____________, an unmeasured excess of a solution containing the magnesium or zinc complex of EDTA is introduced into the analyte solution
displacement titrations
is a
complexing agent that reacts
selectively with a component
in a solution to prevent that
component from interfering in a
determination.
masking agent
A magnesium ion indicator that decomposes less than eriochrome black T
Calmagite
