Orthophenanthroline indicators

Assay With the aid of about 25 mL of water, transfer about 125 mg of sample, accurately weighed, into a 300-mL Erlen-meyer flask. Add 50.0 mL of 0.5 N potassium dichromate, mix, then carefully add 100 mL of sulfuric acid, and heat to boiling. Remove the mixture from the heat, allow it to stand at room temperature for 15 min, cool it in a water bath, and transfer it into a 250-mL volumetric flask. Dilute almost to volume with water, cool to 25°, then dilute to volume with water, and mix. Titrate a 50.0-mL aliquot with 0.1 iV ferrous ammonium sulfate, using 2 or 3 drops of orthophenanthroline TS as the indicator, and record the volume required, in milliliters, as S. Perform a blank determination (see General Provisions), and record the volume of 0.1 N ferrous ammonium sulfate required, in milliliters, as B. Calculate the percent cellulose in the sample by the formula... 

Assay Dissolve about 0.4 g of sample, accurately weighed, in 20 mL of 16 100 sulfuric acid, add 5 mL of 85% phosphoric acid, dilute with approximately 50 mL of water, and immediately titrate with 0.1 N ceric sulfate, using orthophenanthroline TS as the indicator. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1 N ceric sulfate is equivalent to 5.585 mg of Fe. Chloride Heat 100 mg of sample, accurately weighed, with 25 mL of water and 2 mL of nitric acid until the sample dissolves. Cool, dilute to 100 mL with water, and mix. Take 10 mL of this solution, and dilute to 30 to 40 mL with water. Proceed as directed in the Chloride Limit Test under Chloride and Sulfate Limit Tests, Appendix IIIB, beginning with add 1 mL of silver nitrate TS... . Any turbidity produced does not exceed that shown in a control containing 20 pig of chloride (Cl). 

Assay Dissolve about 1 g of sample, accurately weighed, in a mixture of 150 mL of water and 10 mL of sulfuric acid in a 300-mL flask. Add 1 drop of orthophenanthroline TS, and immediately titrate with 0.1 A ceric sulfate prepared as indicated in Volumetric Solutions under Solutions and Indicators. Perform a blank determination (see General Provisions), and make any necessary correction. Each milliliter of 0.1 A ceric sulfate is equivalent to 24.00 mg of Fe(OH2)2 (OOCCH2NH2)2. 

Assay Dissolve about 100 mg of sample, accurately weighed, in 20 mL of water add 40.0 mL of 0.1 N ceric sulfate prepared as directed for Volumetric Solutions under Solutions and Indicators (or use a commercially available solution) mix well and add 2 mL of silver sulfate solution (5 g of Ag2S04 dissolved in 95 mL of concentrated sulfuric acid). Cover, heat nearly to boiling, and continue heating for 30 min. Cool to room temperature, and titrate with 0.1 A ferrous ammonium sulfate to a pale yellow color. Add 2 drops of orthophenanthroline TS, and continue the titration to a salmon-colored endpoint, recording the volume required, in milliliters, as S. Perform a residual blank titration (see General Provisions), and record the volume required as B. Each milliliter of the volume B - S is equivalent to 2.650 mg of NaH2P02H20. 

Dipyridyl and orthophenanthroline form particularly stable complexes with iron. The octahedral [Fe(phcn)3] + ion (Fig. 2C4) is blood-red but is oxidised to pale blue [Fe(phen)3] without any structural change. for the system = 1.14 V, making the compound, also known as ferroin, a most useful redox indicator for the oxidation of Fe + ion Fe +/Fe + = 0.77 V) by cerium(IV) ion (E Ce +/Ce + = 1.45 V). 

Ferroin indicator Dissolve 1.485 g of orthophenanthroline monohydrate in about 80 ml distilled water (warm if necessary and then cool) and add 0.69 g ferrous sulphate heptahydrate. Stir to dissolve and dilute to 100 ml. 

The dichromate is reduced to chromic ion while the ferrous ion is oxidized to ferric ion. When all of the CraO has been reduced, it is possible for Fe + to exist in solution. An indicator called orthophenanthroline is added, which forms a red complex with Fe " and thereby detects the presence of... 

The standard potential (and, of course, the formal potential) exhibited by ferroin may be appreciably modified by the introduction of varied substituents on the 1,10-phenanthroline nucleus. The most important indicators of this series are the derivatives of the 5-nitro ( ° = 1.25 V), 5-methyl (E° = 1.02 V), and 4,7-dimethyl (E° = 0.88 V) orthophenanthroline. 

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