Uranic acid salts

Uranium and Hydrogen—Halogen and Oxyhalogen Compounds—Oxide. and. Hydroxides—Uranic Acid—Salts of Uranic Acid—Peruranic Acid and Peruranates—Compounds with Sulphur, Selenium, and Tellurium. 

Uranium trioxide is slightly basic, but with the exception of uranium hexafluoride, the salts formed by interaction with acids still contain two-thirds of its oxygen in the form of the uranyl radical, compounds of the type UOjR g being produced. On the other hand, however, the oxide acts towards strong bases as an acid anhydride, similar to chromic anhydride, and produces stable uranates. In contact with water it readily forms uranic acid, U02(0H)2. ... 

Potassium Peruranate, (K202)2.U04, is obtained by adding hydrogen peroxide to a solution of uranic acid or peruranic acid in aqueous caustic potash, and precipitating by means of alcohol. The salt is less stable than the corresponding sodium compound. Red peruranates of composition KjUOg and KaUOj.SHaO have been described. ... 

The dihydrate is formed by evaporation at ordinary temperature of an ethereal solution of the hexahydrate which has been dried with calcium nitrate or by crystallisation of the hexahydrate from concentrated nitric acid solution. It yields small lustrous plates, thick and square, probably rhombic, and possessing a green fluorescence. It melts at 179-3° C. It is much more stable than the trihydrate, and can be kept in a vacuum desiccator with caustic alkali or i hosphorus pentoxide without any loss of water. It dissolves readily in ether. If the dihydrate is heated in a current of carbon dio.xide at 98° C. a product corresponding very nearly in composition to the nioiiohydrate, U03(N03)3.H20, is obtained at 160° C. under the same conditions the ankydi ffus salt, U02(N03)2, is obtained. The latter may also be obtained by passing a current of dry nitric anhydride over the tri-hydrate carefully heated at 170° to 180° C. It is a yellow amorphous powder, readily soluble in water with c -olution of heat. It reacts violently with ether. When heated to 200° C. it decomposes and leaves a mixture of uranic acid, UO3.H2O, and uranic anhydride. ... 

When a solution of SeOg is evaporated the acid, HgSeOg, separates as hexagonal prisms. There are normal and acid selenites, and also superacid salts such as KH3(Se03)g. Heteropolyacids are formed with vanadic, molybdic and uranic acids. 

In neutral or masked alkaline solutions of uranyl salts, a quantitative precipitation of a red-brown product is obtained by adding 8-hydroxyquinoline (oxine). In contrast to other metal oxinates, which for the most part are inner complex phenolates, the uranium compound contains also a molecule of oxine as neutral part according to the formulation U02(CoHeNO)2 C9HeNOH.3 Probably this compoimd should not be viewed as uranyl oxinate but rather as the oxine ester of uranic acid, in other words as oxine uranate. 

Uranous Salt. — The solution of 1 gm. of uranium nitrate in 20 cc. of water and 1 cc. of dilute sulphuric acid should be colored red on the addition of 0.1 to 0.2 cc. of decinormal potassium permanganate. 

Many oxidation and reduction reactions, especially in organic chemistry, ai-e in consequence considerably influenced by the presence of uranyl salts under the action of light. The reaction may also be used as a means of preparing uranous salts, by exposing to light a solution of the uranyl salt containing the requisite quantity of the acid entering into the constitution of the salt, and a readily oxidisable substance such as alcohol. In the case of the chloride the reaction is as follows ... 

If insufficient acid is added, basic salts result while if the reaction is allowed to proceed further, a black precipitate of uranous hydroxide is obtained. 

Double fluorides have been obtained by reduction of complex alkali uran d fluoride solutions by means of oxalic or formic acid under the influence of sunlight. The potassium salt, KUFj, is a green powder, insoluble in water. 

The chloride may also be obtained in solution by the reduction of uranyl salts in hydrochloric acid solution, either by means of nascent hydrogen, or by electrolysis in a special apparatus, in which a layer of mercury is used as the cathode, the anode being of carbon, and the whole is cooled in ice. In the latter case, traces of dissolved mercury or platinum are liable to act as negative catalysts and stop the reduction when the uranium is in the tetravalent condition. The solutions of the trichloride obtained contain excess of hydrochloric acid and are purple red they are comparatively stable, but are readily converted into uranous compounds. 

Double Chlorides of the type R2UCI5 (R=Na, K, Li R2=Ca, Sr, Ba) have been obtained by passing uranous chloride vapour over the chloride of the alkali or alkaline earth metal heated to dull redness. The salts, which are green, are hygroscopic, and darken as they absorb moisture from the air. They are unstable, and their solutions oxidise slowly at ordinary temperature and more rapidly when heated. When evaporated in a vacuum over sulphuric acid they decompose, so that the salts cannot be obtained in the crystalline form. 

The double salt, uranous chlorophosphate, UCl4.UH2(P04)2, separates in green crystals from a solution of uranous phosphate, UH2(P04)2.5H20, in concentrated hydrochloric acid. A chlorophosphate, of composition UCI4.3UO2.2P2O5, has also been prepared (see p. 328). 

On a commercial scale uranous oxide is prepared by fusing at red heat a mixture of 35 parts of common salt and 20 parts of sodium uranate with 1 part of powdered charcoal, the heating being continued until the escape of gas ceases. After cooling, the mass is lixiviated with water, and the residue of uranous oxide is washed by decantation. By washing with 5 per cent, hydrochloric acid, any iron, aluminium, or vanadium compounds may be removed, and a commercial product of purity equivalent to 97 per cent. U3O3 is obtained. If the uranous oxide is required for the production of ferro-uranium, the complete removal of iron is not necessary. 

Uranous Hydroxide.—The addition of alkali to a solution of a uranous salt produces a reddish-brown gelatinous precipitate, which darkens in colour on boiling the solution. If dried in vacuo it becomes black and has the composition UOg.HgO. This rapidly oxidises in the air and readily dissolves in dilute acids, forming uranous salts. It acts upon a neutral solution of silver nitrate, first precipitating silver oxide and forming a green solution which, however, soon turns yellow, and the oxide is reduced to metallic silver as the uranyl salt forms in solution, thus ... 

According to Aloy, a black crystalline hydrate, of composition UO2.2H2O, is obtained when crystallised uranous sulphate is treated with hot potassium or sodium hydroxide solution. The product, when thoroughly w ashed, remains stable in air for several days. It dissolves in dilute acids, yielding uranous salts. On heating, it is completely converted to the green oxide. 

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