Applications of Multidentate Complexes

Not surprisingly, a large number of applications take advantage of the chelate effect. In this section, we start by discussing compleocometric quantitative analytical methods, which are those involving the formation of a complex as the key to the measurement of the amount of a material in a sample. 

Complexometric titrimetric methods involve the formation of a metal complex as the end point of a titration. In these procedures a solution of the metal ion is usually 

Due to the especially stable complexes formed by EDTA, it is put to a large number of uses. In one of the most common, EDTA titrations are used to determine the concentrations of hard-water ions, Ca and Mg, in a natural water supply. (More on hard water can be found in Section 6.4 as well as in Section 13.3, pp. xxx-xxx.) Because EDTA ties up so many 2 + and 3 + cations in complex form, these metals are not chemically available to participate in ways they normally would. For this reason, EDTA is sometimes referred to as a sequestering agent, one that isolates and chemically sets aside metal ions. Left free, these trace metals often 

Three different chelating agents (a) triethylenetetra-mine (trien), b) 1,10-phenanthroline (phen), and (c) ethylenediaminetetiaacetic acid (H4EDTA) and the resulting coordinated ions employed in various complexometric titrations. 

EDTA is also used to remove the calcium carbonate and sulfate scales that form in hot-water boilers and heaters. Calcium carbonate precipitates out when hard water is heated because the bicarbonate present in any naturally aerated water supply decomposes under the action of heat into carbonate, water, and carbon dioxide, as shown in Equation (6.15). (This reaction is the source of some of the very small bubbles that form on the sides of a beaker before water heated in it comes to a boil.) The carbonate is then available to be precipitated by calcium, magnesium, or iron cations that are often present in a natural water supply. This precipitation reaction is shown for calcium in Equation (6.16)  

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