Ferric salts, color

Deep red coloration. Boil for one minute and note the formation of a brown ppt. of basic ferric salt. Add dil. HCl the ppt. dissolves, giving a clear solution. 

Fenton s reagent. To a solution of tartaric acid or a tartrate add 1 drop of freshly prepared ferrous sulphate solution, i drop of hydrogen peroxide solution and then excess of NaOH solution an intense violet coloration is produced, due to the ferric salt of dihydroxyfumaric acid, HOOC C(OH) C(OH)COOH. 

In 1877, Nencki (22) condensing ammonium thiocyanate with chloroacetic acid, attributed the name rhodaninic acid (Rhodaninsaure) to the compound he obtained. He noted the ability of rhodaninic acid to give colored derivatives with ferric salts. 

Ana.lytica.1 Methods. Thiocyanate is quantitatively precipitated as silver thiocyanate, and thus can be conveniendy titrated with silver nitrate. In the presence of a ferric salt, a red-brown color, produced by the ferric thiocyanate compex, indicates the end point. 

Aq solns of ferric azide have a deep red coloration similar to that produced by Fe(CNS)s. This characteristic coloration is also produced when ferric salts are added to aq solns of hydrazoic acid, thus serving as a colorimetric test for HN3(Ref 3)... 

Ferric Salts,—The solution of 1 gm. of powdered ferrous ammonium sulphate in 20 cc. of boiled and cooled water (freed from oxygen), with 1 cc. of hydrochloric acid, should not afford an immediate red color on adding a few drops of potassium sulphocyanate solution. 

It is obvious that such a definition will include molecules which are not tannins in the commercial sense of being economically important in the tanning of hides, but will exclude a large number of substances whose only relationship to the tannins is their capacity to reduce alkaline permanganate or give colors with ferric salts. 

The product should be stored out of light. Cold aqueous solutions of pure potassium hexathiocyanatochromate (III), when freshly prepared, give no color with ferric salts. In... 

The ferric salts of benzoic, succinic, hydroferrocyanic, gallic and tannic acids are sparingly soluble in cold water, while basic ferric salts of formic and acetic acids formed on boiling are also sparingly soluble. Solutions of ferric thiocyanate and salicylate exhibit characteristic colorations. 

If the addition of the ferric salt produces a brownish coloration owing to the presence of tannin in the solution and so masks any coloration due to salicylic add, it is necessary to repeat the extraction on the residue obtained, after acidifying it with a few drops of dilute hydrochloric acid. 

Rutkowski (33) reported the simultaneous colorimetric assay of salicylamide, salicylic acid and genetisic acid in pharmaceutical preparations. These compounds give hlue color complexes with ferric salt (nitrate in ethanol solution). The blue color complex of salicylamide is extracted with ether while the others are not. 

Stirring is continued for one hour after all the diazo solution has been added. The mixture is now filtered and the filtrate concentrated to a volume of approximately 51. this is deep brown in color. Concentrated hydrochloric acid is added in small portions, and the tarry material which separates is filtered off. The add is added until after filtering a clear, pale yellow solution results. The phenylarsonic add is now precipitated by the addition of more hydrochloric acid. An excess must be avoided since it causes a certain amount of the phenylarsonic acid to go into solution. When this neutralized mixture has cooled, the product is filtered off and washed with a little distilled water. Small quantities of phenylarsonic acid remaining in the filtrate may be predpitated as the ferric salt by adding ferric chloride. The yield of white or cream-colored product averages more than 800 g. (50%) and in many cases runs well over 1000 g. (62%). After recrystallization from water the product is practically white and softens at 158°, passing into the infusible anhydride, C6H5ASO2. 

Similar to the halides is the thiocyanate, Hg(SCN)2. This compound is also very slightly dissociated, and, consequently, mercuric ions in solution may be titrated with a standard solution of sodium thiocyanate, using a bit of ferric salt as an indicator the end point is marked by appearance of the blood-red color of the FeSCN2+ ion. Students enjoy this titration, not only because the end point is sharp, but also because the solid Hg(SCN)2 so formed may be filtered off, dried, and ignited, whereupon it evolves a voluminous, serpentlike ash (Pharaoh s serpents). 

Ferric Salts Potassium ferrocyanide TS (10%) produces a dark blue precipitate in acid solutions of ferric salts. With an excess of 1 N sodium hydroxide, a red-brown precipitate is formed. Solutions of ferric salts produce with ammonium thiocyanate TS (1.0 AO a deep red color that is not destroyed by diluted mineral acids. 

Sulfuric acid was often used, either alone or in conjunction with other oxidants such as ferric salts, to convert phenothiazine drugs and their metabolization products into the colored radical species, which may then be identified and estimated by spectrophotometry. Rieder found the absorption maximum of the... 

Experiment 189. — (a) Put a few grams (3 to 5) of iron filings in a test tube, add about 10 cc. of dilute hydrochloric acid, and warm gently. Ferrous chloride is formed (in solution), (i) Pour a little into a test tube one-third full of sodium hydroxide solution. The precipitate is ferrous hydroxide. Watch the changes in color. To what are the changes due (2) Add a second portion to potassium ferricyanide solution. The precipitate is ferrous ferricyanide. Describe it. (3) Add a third portion to potassium thiocyanate solution. If ferric salts are absent, no change results. (4) Add a fourth portion to potassium ferrocyanide solution. The precipitate is ferrous ferrocyanide. Describe it. 

The hydrolysis of ferric salts is so common that the color of ferric ion, Fe(H20)g+ + , is usually masked by that of the hydroxide complexes. Ferric ion is nearly colorless it eems to have a very pale violet color, seen in crystals of ferric alum, KFe(SO )o I2H.2O, and ferric nitrate, Fe(N03)3 9H20, and in ferric solutions strongly acidified with nitric or perchloric acid. Solutions of ferric salts ordinarily have the characteristic yellow to brown color of the hydroxide coniplexe Fe(H20)50H + + and Fe(H20)4(OH)o+, or even the red-brown color of colloidal particles of hydrated ferric hydroxide. 

Ferric Compounds. The hydrated ferric ion, Fe(H20)g+ + +, is pale violet in color. The ion loses protons very readily, however, and ferric salts in solution usually are yellow or brown, because of the formation of hydroxide complexes. Ferric nitrate, Fe(N03)3 6H20, exists as pale violet deliquescent crystals. Anhydrous ferric sulfate, Fe2(S04)g, is obtained as a white powder by evaporation of a ferric sulfate solution. A well-crystallized ferric sulfate is iron alum, KFe(S04)2 12H20, which forms pale violet octahedral crystals. 

Xanthurenic acid is easily detectable and measurable through the reaction, now well known, of forming a green color with ferrous or ferric salts. In 1951 Musajo and Coppini after many attempts perfected an analytical procedure which allows the quantitative determination of kynurenic and xanthurenic acids, separately or mixed, in amounts of at least 100 [ig, also when occurring in urine (M17). 

The iron salts of ferro and ferricyanic acid are the compounds to which the names cyanogen and cyanide are due. Two of these salts are of deep blue color and the Greek word from which cyanogen and cyanide are derived is cyanos which means blue. The ferric ferro-cyanide, Fe4 "(Fe"(CN6)3, is known as Prussian blue and the ferrous ferri-cyanide, Fe3"(Fe" (CN)6)2, is Turnbull s blue. These compounds are formed when ferric salts in solution are treated with potassium ferro-cyanide and when ferrous salts in solution are treated with potassium ferricyanide. They are common qualitative tests for the two forms of iron salts. The compounds are also used as laundry blueing and are formed in the blue print process of photography. 

Inks.—Formerly all writing inks except so-called India ink, which is a carbon product, were made by the treatment of ferric salts with tannin or tannic acid. The green solution produced with excess of the iron salt becomes black on drying and exposure to the air. Such iron inks may be bleached by means of oxalic acid which reduces the colored ferric compound, produced with the gallotannic acid, to a colorless compound. At the present time many writing inks are made from aniline dyes. These are not bleached with oxalic acid, but are... 

Phenol is a reducing agent and is capable of reacting with ferric salts in neutral to acidic solutions to form a greenish-colored complex. Phenol decolorizes dilute iodine solutions, forming hydrogen iodide and iodophenol stronger solutions of iodine react with phenol to form the insoluble 2,4,6-triiodo-phenol. 

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