Prussian Blue water solution

In the first experiment 10 ml of 500 ppm solutions of FeCl3 were sonicated for 15, 30, 45 and 60 min. To examine the reduction of Fe(III) to Fe(II), 0.1 ml of the sonicated sample was transferred to a 10 ml volumetric flask and mixed with 0.5 ml of 2,000 ppm K3[Fe(CN)6] solution before making up to the mark with distilled water. Final concentration of this sonicated sample in 10 ml of volumetric flask was 5 ppm. UV-vis absorbance at >.max 795 was recorded. Sonication reduced Fe3+ to Fe2+, which reacted with K3[Fe(CN)6], already added in the solution, to form blue colour due to prussian blue. Continuous sonication gradually increased the concentration and intensity of prussian blue complex, as is clear from the Table 10.1. 

Metal hexacyanoruthenates possess a lower symmetry. Several compounds have highly disordered structures, especially when no alkali cations are present for charge compensation. Such a complex defect structure has been found for a completely potassium free Prussian blue precipitated very slowly from a solution in concentrated hydrochloric acid [25, 26]. Here, the structure still remains cubic face-centered however, one-third of the [M1 -1(CN)6] is vacant, randomly distributed and that space is filled with water molecules. The coordination sphere of the remaining ions is maintained... 

TO EACH, ADD A FEW DROPS OF SOLUTION OF /4 TEASPOON POTASSIUM FERROCYANIDE IN 50 ml WATER. FERRIC SALT MAKES A DEEP BLUE PRECIPITATE OF PRUSSIAN BLUE. FERROUS SALT MAKES LIGHT BLUE PRECIPITATE. 

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)6]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkali or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial applications, although the majority of industrial production of iron cyanide complexes is of iron blues such as Prussian Blue, used as pigments (see PIGMENTS, inorganic). Many transition-metal salts of [Fe(CN) J4"" have characteristic colors. Addition of [Fe(CN)6]4 to an unknown metal salt solution has been used as a qualitative test for those transition metals. 

All of the [Fe(CN) J4- salts may be considered salts of ferrocyanic acid or tetrahydrogen hexakiscyanoferrate [17126-47-5], H4[Fe(CN)J, a strongly acidic, air-sensitive compound. It is soluble in water and alcohol but is insoluble in ether. It can be prepared by precipitation of an etherate by adding ether to a solution of [Fe(CN) J4"" that was acidified with concentrated sulfuric acid. Removal of the ether of solvation affords a white powder which is stable when dry but slowly turns blue in moist air because of Prussian Blue formation. 

Test for Hydrocyanic Acid.—2 5 grams of the substance are digested for an hour with 30 c.c. of water and a few drops of potassium hydroxide solution, the liquid being then rendered add with sulphuric add and distilled, the first 3 c.c. of distillate being collected and tested by means of the Prussian blue reaction, which is carried out as follows ... 

Cyanide ion, and hence nitrogen in the sample, may be detected by the Prussian Blue test. The filtered alkaline solution, resulting from the action of water upon the sodium fusion, is treated with iron(n) sulphate and thus forms sodium hexacyanoferrate(n). Upon boiling the alkaline iron(n) salt solution, some iron(m) ions are inevitably produced by the action of air upon addition of dilute sulphuric add, thus dissolving the iron(n) and (hi) hydroxides, the hexa-cyanoferrate(n) reacts with the iron(m) salt producing iron(m) hexacyano-ferrate(n), Prussian blue ... 

Small Quantities or Solutions. Wear eye protection, laboratory coat, and nitrile rubber gloves. In the fume hood, add the sodium cyanide to a solution of 1% sodium hydroxide (about 50 mL/g of cyanide). Household bleach (about 70 mL/g of cyanide) is slowly added to the basic cyanide solution while stirring. When addition of the bleach is complete, the solution can be tested for the presence of cyanide using the Prussian blue test To 1 mL of the solution to be tested, add 2 drops of a freshly prepared 5% aqueous ferrous sulfate solution. Boil this mixture for at least 60 seconds, cool to room temperature, and then add 2 drops of 1% ferric chloride solution. The resulting mixture is made acid to litmus with 6 M hydrochloric acid (prepared by adding concentrated acid to an equal volume of cold water). If cyanide is present, a deep blue precipitate will form. (Concentrations of cyanide greater than 1 ppm can be detected.) If the test is positive, add more bleach to the cyanide solution, and repeat the test. Continue until no Prussian blue precipitate is formed. Wash the solution into the drain.4 6... 

Potassium ruthenocyanide crystallises in square pseudo-rhombic plates, isomorphous with the corresponding ferro- and osmo-cyanides.2 Its solution in water yields no precipitate with salts of the alkaline earth metals as their ruthenocyanides are soluble. Ferric chloride gives a rich purple precipitate resembling Prussian blue in its chemical properties. Soluble in pure w ater it is precipitated by salts or alcohol. When precipitated in cotton fibre it adheres well, imparting its own beautiful colour. Alkalies decompose the salt, which, however, is re-formed on addition of dilute acid. This constitutes a useful test for ruthenocyanides. 

Add a freshly prepared 10% solution of ferrous sulphate in freshly boiled and cooled water a precipitate of ferrous hydroxide is formed. Add sufficient dilute hydrochloric acid to dissolve the precipitate a blue colour (Prussian Blue) indicates the presence of cyanide. 

The Prussian blue reaction may be rendered more convenient in use by employing a reaction paper. For this purpose Ganassini s paper is strongly recommended. It is prepared by immersing a strip of filter paper, just before use, in a mixture of 10 ml. 10% ferrous sulphate solution (containing a trace of ferric salt) and 20 ml. of an alkaline solution of Rochelle salt (30 gm. Rochelle salt, 10 gm. potassium hydroxide and 100 ml. water). This paper should be exposed first to the atmosphere containing hydrocyanic acid and then to hydrochloric vapour, when it becomes greenish-blue. 

Cleaning Up Add the aqueous filtrate to 10 mL of a 1% sodium hydroxide solution. Add 50 mL of household bleach (5.25% sodium hypochlorite) to oxidize the cyanide ion. The resulting solution can be tested for cyanide using the Prussian blue test described in Chapter 70, Part 3a. When cyanide is not present, the solution can be diluted with water and flushed down the drain. Ethanol used in crystallization should be placed in the organic solvents container. 

The iron compounds have been known for several centuries and valued as pigments. The name Prussian (Berlin) blue is given to the compound formed from a solution of a ferric salt and a ferrocyanide, while that obtained from a ferrous salt and a ferricyanide has been known as Turnbull s blue. It appears from Mbssbauer studies that both of these compounds are (hydrated) Fe4 [Pe (CN)6]3. with high-spin Fe and low-spin Fe in the ratio 4 3. There is also a soluble Prussian blue with the composition KFe[Fe(CN)6] which is also a ferrocyanide. Most, if not all, of the compounds we are discussing are hydrated we consider the water of hydration later. 

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