Ferrous acid ferrocyanide

Keith WG, Powell RE (1969) Kinetics of decomposition of peroxynitrous acid. J Chem Soc (A) 90 Keyer K, Imlay JA (1997) Inactivation of dehytratase [4F3-4S] clusters and disruprion of iron home-stasis upon cell exposure to peroxynitrite. J Biol Chem 272 27652-27659 Khaikin Gl, Alfassi ZB, Huie RE, Neta P (1996) Oxidation of ferrous and ferrocyanide ions by peroxyl radicals. J Phys Chem 100 7072-7077... 

Upon prolonged exposure to light, a solution of potassium ferrocyanide deposits Prussian blue (see p. 225), whilst on continued boiling ammonia is evolved. WTith ferrous salts it yields an immediate white precipitate of ferrous potassium ferrocyanide, K2Fe[Fe(CN)6], which readily absorbs oxygen, becoming blue. The presence of dilute hydrochloric or sulphuric acid, or the employment of excess of the ferrous salt, accelerates the formation of the blue colour, and the reaction is exceedingly delicate.12... 

Ferrous hydrogen ferrocyanide, H2Fe[Fe(CN)6], results when hydrogen ferrocyanide solution is heated to 110°-120° C.4 with exclusion of air. It readily oxidises to ferric hydrogen ferrocyanide, Fe H[Fe (CN)6].H20, which is a blue compound, insoluble in water, oxalic acid, and ammonium oxalate solutions. 

Ferric chloride solution is then added to com ert the sodium ferrocyanide to the deep blue ferric ferrocyanide (or Prussian Blue), dilute sulphuric acid being also added to dissolve any ferrous and ferric hydroxides present in the other-... 

Upon boiling the alkaline ferrous salt solution, some ferric ions are inevitably produced by the action of the air upon the addition of dilute siilphurio acid, thus dissolving the ferrous and ferric hydroxides, the ferrocyanides reacts with the ferric salt producing ferric ferrocyanide (Prussian blue) ... 

Ferric ammonium ferrocyanide—The blue pigment obtained by oxidising under acidic conditions with sodium dichromate the acid-digested precipitate resulting from mixing solutions of ferrous sulfate and sodium ferrocyanide ia the presence of ammonium sulfate. The oxidized product is filtered, washed, and dried. The pigment consists principally of ferric ammonium ferrocyanide with small amounts of ferric ferrocyanide and ferric sodium ferrocyanide. 

Put 20 g. of potassium ferrocyanide in a 250-cc. Erlenmeyer flask, adding 30 cc. of water. Place the flask on the water bath and heat till the ferrocyanide dissolves. Add 35 cc. of nitric acid (sp. gr., 1.24) and continue heating until a test portion shows no blue color but a dark green precipitate when treated with ferrous sulfate. Let stand for a day or two and filter off the tarry impurities. Now neutralize with sodium carbonate, taking care that no excess is added. Warm and, when cool, add from one to two times the volume of alcohol (ethyl). Set the flask in a dry place for a day or two, after which the impurities (chiefly crystals of potassium nitrate) may be filtered off, and the nitro-prusside crystallized out. Sometimes two or three treatments with alcohol are necessary. In order to expedite the operation of evaporating down to crystallization, the solution may be evaporated by heating in a suction flask under reduced pressure. Quick crystallization increases the yield. The yield should be above 75 per cent. 

Sulphates, Copper, and Alkalies. — Boil for a few minutes a solution of 5 gm. of ferrous chloride in 10 cc. of water and 5 cc. of nitric acid (sp. gr. 1.3), dilute to 120 cc., add 20 cc. of ammonia water, and filter evaporate 50 cc. of the filtrate and ignite the residue. The weight of the latter should not exceed 0.001 gm. Slightly acidulate 20 cc. of the filtrate with hydrochloric acid and add barium nitrate solution. No change should appear. 20 cc. of the filtrate acidified with acetic acid should show no change upon addition of potassium ferrocyanide solution. 

Fe4(Fe(CN)6)3 (c). Berthelot27 measured the heat of reaction of aqueous ferrocyanic acid with ferric hydroxide to be 76.6, and the heat of reaction of aqueous KCN with aqueous ferrous and ferric sulfates to be 225.0 whence, for ferric ferrocyanide, Qf=— 322.5 and —312. 

Experiment Prepare a solution of a ferrous salt by dissolving 2 grams of ferrous ammonium sulphate in 20 cc. of water, adding a little dilute sulphuric acid and a piece of iron wire. Test both this solution and a solution of a ferric salt (nitrate or chloride) with potassium ferrocyanide, potassium ferricyanide, and potassium sulphocyanate. Tabulate the results. These constitute the standard tests for ferrous and ferric salts. Write equation. 

Occluded hydrogen is more reactive chemically than the normal gas. Hydrogenated palladium precipitates mercury and mercurous chloride from an aqueous solution of the dichloride, without any evolution of hydrogen. It reduces ferric salts to ferrous potassium ferricyanide to ferrocyanide chlorine water to hydrochloric add iodine water to hydriodic acid 2 chromates to chromic salts ceric to cerous salts whilst cupric, stannic, arsenic, manganic, vanadic, and molybdic compounds are also partially reduced.3... 

The chemical activity of the absorbed hydrogen is considerably enhanced. For example, the hydrogenated sponge when placed for twenty-four hours in the dark at ordinary temperatures in dilute solutions of ferric salts reduces them to the ferrous condition. In a similar manner potassium ferricyanide is reduced to ferrocyanide chlorine water to hydrochloric acid and iodine water to hydriodic acid.2... 

Sodium Ferrocyanide Prepare a Sample Solution by dissolving 9.62 g of sample in 80 mL of water in a 150-mL glass-stoppered cylinder or flask. Prepare a Standard Solution containing 125 pig of sodium ferrocyanide [Na4Fe(CN)6], in each milliliter by dissolving 99.5 mg of decahydrate ferrocyanide [Na4Fe(CN)6-10H2O] in 500.0 mL of water. Transfer 1.0 mL of Standard Solution into a similar 150-mL container for the control. Add 2 mL of ferrous sulfate TS and 1 mL of 2 N sulfuric acid to each container, dilute to 100 mL with water, and mix. Transfer 50-mL portions of the sample and control solutions into matched color-comparison tubes. The Sample Solution shows no more blue color than the control. 

Iron blues, or cyanide iron blues, are complex ferriferrocyanide, generally with ammonium, potassium, or sodium cations. They are most commonly produced by a two-step process. First, ammonium, potassium, or sodium ferrocyanide, M4[Fe(CN)6], is reacted with ferrous sulfate, FeS04, to yield M2Fe[Fe(CN)]6. The latter is digested with hot sulfuric acid and oxidized with sodium chlorate or sodium bichromate to yield the ferric ferrocyanide M(Fe[Fe(CN)6]. ... 

Hydrogen ferrocyanide is soluble in water and possesses a strong acid reaction. The solution decomposes on boiling, evolving gaseous hydrogen cyanide, and yielding a white precipitate of ferrous cyanide. Thus —4... 

Another method 2 consists in passing the vapour of trimethylamine into a retort at red heat. The resulting products are passed into sulphuric acid, whereby ammonium cyanide is converted into hydrogen cyanide, which is now absorbed in potash to yield the corresponding cyanide. Ferrous hydroxide, prepared by addition of milk of lime to a solution of ferrous chloride, is added to the cyanide solution, and the liquid, after filtering, deposits a relatively pure crop of potassium ferrocyanide. 

It may be conveniently prepared by heating potassium ferrocyanide with 50 per cent, nitric acid solution on a water-bath until a drop of the solution gives no colour with ferrous sulphate. The whole is cooled, the liquid poured from the precipitate, neutralised with sodium carbonate, and taken to dryness. Extraction with water, filtration from the insoluble iron compounds, and crystallisation from the clear aqueous solution yields the salt in ruby-coloured, rhombic prisms. The reactions involved may be represented as follows —... 

Wet Tests.—The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate—Turnbull s blue—is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not d troyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present. 

Ferrous and ferric iron—ferricyanide and ferro-cyanide tests. To 2 (hops of sample add 3 (hops of 2Mhy(hochloric acid and 1 drop of 1% potassium ferricyanide solution. A deep blue precipitate indicates ferrous iron. Repeat the test but adding 1 drop of 1% potassiiun ferrocyanide solution. A deep... 

Copper, Nitric Acid, etc. (Alkali Salts, Calcium). — Dilute 20 iM. of ferric chloride solution (1 1) with 100 cc. of water, fuld 25 cc. of ammonia water, and filter. On evaporating 50 cc. of the colorless filtrate and igniting the residue, the weight of the latter should not exceed 0.001 gm. On mixing 2 cc. of the filtrate with 2 cc. of concentrated sulphuric acid, and overlaying tliis mixture with 1 cc. of ferrous sulphate solution, no brown zone should form at the contact-surfaces of the two licpiids. 20 cc. of the filtrate acidulated With acetic a

potassium ferrocyanide solution. 

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 Prussian Blue Reaction. On addition to an alkaline solution of hydrocyanic acid of a few ml. of ferrous sulphate solution and of ferric chloride solution, then shaking and warming, a blue precipitate of ferric ferrocyanide appears on acidification with hydrochloric acid. In presence of only a trace of hydrocyanic acid, only a greenish-blue colouration appears, due to the formation of a colloidal suspension of the ferric ferrocyanide. On standing (sometimes for as long as 12 hours) the suspension settles to blue floes, leaving the supernatant solution colourless. 

Detection of cyanide ion and other tests for nitrogen. The cyanide is converted first to ferrocyanide ion by boiling with ferrous sulfate, then to ferric ferrocyanide, or Prussian blue, by addition of ferric chloride and addition of acid. The Prussian blue is detected by its blue color, which is intensified by addition of fluoride ion ... 

The above reaction occurs rapidly at pH levels below 3. Because the acidic properties of ferrous sulfate are low at high dilutions, acid must be added for pH adjustment. The ferrous sulfate reducing process generates large volumes of sludge and thus its use is rare in large-scale treatment facilities. In addition, the use of ferrous sulfate to treat chromate wastes containing cyanide results in the formation of very stable ferrocyanide complexes, which prevent subsequent effective cyanide treatment. 

Still a third method is to oxidise ferrous sulphate with nitric acid and mu into the solu potassium ferrocyanide solution. Tire deep bine precipitate is collected and washed until from iron. 

Test for a Soluble Cyanide (Section 240).—To 1 cc. of a dilute solution of potassium cyanide add 5 drops of a solution of sodium hydroxide and 5 drops of a solution of ferrous sulphate heat to boiling, cool, and add dilute hydrochloric acid, drop by drop, until the solution shows an acid reaction. If no color develops add 3 drops of a solution of ferric chloride. Potassium ferrocyanide is formed from the potassium cyanide and ferrous sulphate the ferrocyanide and the ferric salt then form Prussian blue. (Eqs.)... 

NOTE.—It is usually not necessary to add ferric chloride, since the ferrous sulphate contains enough ferric salt to give the reaction. An excess of hydrochloric acid should be avoided since it interferes with the formation of the ferric ferrocyanide. 

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