Ferric alums hydrates

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. 

The hexaquo ion exists in very strongly acid solutions of ferric salts, in the several ferric alums, MIFe(S04)2- 12H20, and presumably also in the highly hydrated crystalline salts. 

As a preliminary, ferric sulfate is made by the oxidation of ferrous sulfate. Dissolve 100 g. of ferrous sulfate in 100 cc. of boiling water, to which has been added before heating 10 cc. of sulfuric acid. Add concentrated nitric acid portionwise to the hot solution, until a diluted sample gives a reddish-brown (not black) precipitate with ammonia. This will require about 25 cc. Boil the solution down to a viscous liquid to get rid of excess nitric acid, dilute to about 400 cc., and add the calculated weight of ammonium sulfate. The crystallization is conducted as in the former exercise, preferably under 20°. By the addition of potassium sulfate, the corresponding potassium iron alum may be secured. In this case, it is necessary to concentrate the solution until there is about four parts of water to one of the hydrated alum and cool to about zero to secure crystallization. Both of these alums are amethyst in color, the potassium salt being much less stable and having a rather low transition point. 

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. 

Incompat Acids, alkalies, alum, ammonia water, amyl nitrite benzoates betanaphthol, phenol, calomel, chloral hydrate, copper sulfate, ferric chloride ferrous sulfate chromium trioxide (chromic acid), cinchona alkaloids, hydrocyanic acid iodides iodine Lead subacetate mercuric chloride, orthoform potassium permanganate, resorcinol, sod. bicarbonate sod. salicylate (in powder) soln arsenic and mercury iodide, spirit nitrous ether (unless prescribed with sod, bicarbonate), syrup ferrous iodide, tartar emetic tannic acid, thymol, urethane, infusions of catechu, cinchona, rose leaves and uva ursi tinctures of catechu, ferric chloride, cinchona, hamanielis iodine, kino, and rhubarb. 

The pH found in Example 5-2 is quite low, showing that the mercuric ion has the property of a weak acid of approximately the same strength as acetic acid. The acid strength of some metal ions is quite considerable. For example, the pH of equimolar H3PO4 and solutions are similar. The strong acid properties of hydrated metal ions become evident in processes such as coagulation/flocculation, where hydrated aluminum sulfate (alum) or ferric chloride is added to a natural water that is buffered with bicarbonate. The metal ion "titrates" (or reacts with) a stoichiometric amount of alkalinity, just as the addition of an equal amount of strong mineral acid would. 

The bronze age did not arrive in China until around 1500 bce, and iron appeared only about 500 bce, but by the beginning of their alchemical age, around 100 ce, the Chinese had knowledge of zinc and brass (a copper-zinc alloy), mercury, sulfur, and several of the common salts, such as niter. In the 400s bce an administrator made a list of known materials that included lead oxide, lead carbonate, sulfur, calcium carbonate, hydrated calcium sulfate, ferric oxide, niter, talc or soapstone, hydrated magnesium silicate, alum (the double sul-... 

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