Chromimetry

We begin this chapter with the study of three important titration methods involving quantitative oxidization reactions. They are based on oxidizations with permanganate, dichromate, and ceric ions. These methods are sometimes (notably in the french literature) called manganimetry, chromimetry, and cerimetry, respectively. Next, we very briefly mention three titration methods involving reduction reactions. 

Titrations with Dichromate Ions Chromimetry 20.2.1 Definition... 

The term chromimetry refers to all the titrimetric methods using standardized solutions of potassium dichromate K2Cr2(>7. Titrations with chromous ions Cr + are not taken into account in the term chromimetry. ... 

Chromium at oxidation state -i-III is under the form of chromic ions Cr + Chromic hydroxide Cr(OH)3 already precipitates at weakly acidic pH [Als(Cr(OH)3)= 10 °]. The predominance diagram /pH of the different species of chromium is given in Fig. 20.3. The couple used in chromimetry is Cr207 /Cr +. Hence, it is practiced only for pH <4. The half-redox reaction is... 

Chromimetry is used in inorganic and organic analysis. We mention the following... 

In organic analysis, most of the time the determinations involving dichromate ions are back titrations. The dichromate in excess is determined by indirect iodometry. Several organic compounds can be determined by chromimetry, including ethylenics, alcohols, carboxylic acids, and aldehydes. The reaction products are usually water and carbon dioxide. Ethanol gives acetic acid. This reaction is used to determine the alcohol level in blood. 

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