COMPLEXATION AND PRECIPITATION REACTIONS IN TITRATION Flashcards
are widely used in analytical chemistry.
One of the earliest uses of these reactions was for titrating cations.
Complexation reactions
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
common inorganic ligands
Water, Ammonia, and Halide Ions
The number of covalent bonds that a cation tends to form with electron donors is its ___
coordination number.
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 ____ , have been used for more than a century.
complexometric titrations
Remarkable growth in their analytical application, based on a particular class of coordination compounds called
chelates
A ligand that has a single donor group, such as ammonia, is called
unidentate
has two groups available for covalent bonding, is called
bidentate
molecules containing nine or more atoms in the cycle and include at least three heteroatoms, usually oxygen, nitrogen or sulfur.
MACROCYCLES
Earliest complexation reaction used in analytical chemistry
Complexometric Titration -
is one of the oldest analytical techniques, dating back to the mid-1800s
It is based on reactions that yield ionic compounds of limited solubility
Precipitation Titration
Titrations with silver nitrate are sometimes called
argentometric titrations
is one of the most common argentometric methods. In this method, silver ions are titrated with a standard solution of thiocyanate ion.
The Volhard method
sodium chromate serves as the indicator for the argentometric titration of chloride, bromide, and cyanide ions -
Mohr Method
uses an adsorption indicator
Fajans Method
first described by K. Fajans, a Polish chemist in 1926
Is an organic compound that adsorbs onto or desorbs from the surface of the solid in a precipitation titration
Adsorption Indicator
is the most widely used complexometric titrant
it has six potential sites for bonding a metal ion: the four carboxyl groups and the two amino groups, each of the latter with an unshared pair of electrons
Ethylenediaminetetraacetic Acid (EDTA)
is a typical metal-ion indicator that is used in the titration of several common cations
Eriochrome Black T
If direct indicator for the analyte is unavailable, a small amount of a metal ion for which a good indicator is available can be added. The metal ion must form a complex that is less stable than the analyte complex.
Methods Based on Indicators for an Added Metal Ion
Potential measurements can be used for end-point detection in the EDTA titration of those metal ions for which specific ion electrodes are available.
Potentiometric Methods
Measurement of UV/visible absorption can also be used to determine the end points of titrations. In these cases, a spectrophotometer responds to the color change in the titration rather than relying on a visual determination of the end point
Spectrophotometric Methods
are useful for the determination of cations that form stable EDTA complexes and for which a satisfactory indicator is not available.
Back-titrations
an unmeasured excess of a solution containing the magnesium or zinc complex of EDTA is introduced into the analyte solution. If the analyte forms a more stable complex than that of magnesium or zinc
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
is often used as a masking agent to permit the titration of magnesium and calcium ions in the presence of ions such as cadmium, cobalt, copper, nickel, zinc, and palladium.
Cyanide ion
which forms the least stable EDTA complex of all of the common multivalent cations in typical water samples, is not titrated until enough reagent has been added to complex all of the other cations in the sample.
Magnesium
