Titrations According To The Reaction Type - Hanna Instruments Hi934 Bedienungsanleitung

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The potential that develops in the electrochemical cell is the result of the free energy change that would occur if the
chemical phenomena were to proceed until the equilibrium condition has been satisfied.
There are many types of titrations where potentiometry can be used, e.g. pH electrodes for acid-base titrations, platinum
ORP electrodes in redox titrations, ion selective electrodes, such as chloride or fluoride for a specific ion titration, and
silver electrodes for argentometric (silver-based) titrations.
2.1.3. SPECTROPHOTOMETRIC TITRATIONS
The name comes from the method used to detect the endpoint of the titration, not its chemistry. Highly colored indicators
that change color during the course of the titration are available for many titrations. More accurate data on the titration
curve can be obtained if the light absorption is monitored instrumentally using a light source, a simple monochromator
and a photodetector, rather than visually determining the color or light absorption change. Light absorption by either an
indicator or by one of the reactants or products can be used to monitor the titration.
Figure 2, shows two titration curves. In graph A the absorption of a metal-indicator complex is being monitored. The
absorption is constant while the metal is complexed by the EDTA titrant. The metal indicator complex was stripped,
causing a sharp break in the titration curve. The point where all the metal is complexed and stripped from the indicator
is the equivalence point. This point is marked by "e.p." on the graph.
In the second titration curve, graph B, the metal complex is being measured while being titrated with EDTA. The new
complex being formed is not colored and does not absorb light. The extrapolated intersection of the two lines determines
the equivalence point.
Figure 2

2.2. TITRATIONS ACCORDING TO THE REACTION TYPE

2.2.1. KARL FISCHER TITRATIONS
This method is based on a well-defined chemical reaction between water and the Karl Fischer reagent. The chemistry
provides excellent specificity for water determination. The method can be used to determine free and bound water in a
sample matrix. The Karl Fischer method is widely considered to produce the most rapid, accurate and reproducible results
and has the largest detectable concentration range spanning 1 ppm to 100%.
The determination of water content is one of the most commonly practiced methods in laboratories around the world.
Knowledge of water content is critical to understanding chemical and physical properties of materials and ascertaining
product quality. Water content determination is conducted on many sample types including pharmaceuticals and
cosmetics, foods and natural products, organic and inorganic compounds, chemicals, solvents and gases, petroleum and
plastic products as well as paints and adhesives. The KF method is verifiable and can be fully documented. As a result,
Karl Fischer titration is the standard method for analysis of water in a multitude of samples as specified by numerous
organizations including the Association of Official Analytical Chemists, the United States and European Pharmacopoeia,
ASTM, American Petroleum Institute, British Standards and DIN.
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