Solutions of precipitates

Re-solution of precipitated ferric hydroxide consumes hydrogen ions. These reactions provide a buffering effect against rapid pH fluctuations by maintaining the pH in the range 2.0—2.2 due to precipitation and resolubilization of ferric iron (Duncan and Walden, 1972). Other acid-generating reactions which involve ferric and other ions are the formation of jarosites (eqn (3)) ... 

The number of units per ml. in each case equals the inverse of the dilution required to give 0.50 mg. of reducing sugar as glucose. Filter paper (F.P.) and cotton activity is also expressed as the mg. of glucose produced by undiluted culture filtrate, or a solution of precipitated enzyme at 5 mg./ml., in the standard test. All values were corrected for appropriate enzyme and substrate blanks. 

Solution of precipitated Sb in H2S04and titration with KMnO. ... 

Consideration of precipitation also plays a major role in describing and understanding selective solution of precipitates and minerals in the laboratory, process plant, and in the environment. 

Adding Na3[Bi(S203-KS,xC>)3] to an ethanohc solution of precipitates yellow K3[Bi(S203-KS,xO)3]. The test is very sensitive, depending, however, on the amount of ethanol present. Apparently NH4 and Ba interfere. The reagent is unstable. 

Solutions of precipitate Zn " as a white zinc oxalate, ZnC204 2H20, soluble in acids and alkalis. 

Reduced chalcogens. Sulfane, H2S, precipitates some of the Zn as ZnS, white, from solutions not too acidic with enough CH3CO2 to consume the H3O, precipitation is complete. Alkaline solutions of precipitate ZnS completely except for a small solubility in excess sulfide, although a large excess of NH3, OH" or Cl" etc. tends to inhibit the reaction. 

Eliminate extraneous materials for separation. The third option is to eliminate extraneous materials added to the process to carry out separation. The most obvious example would be addition of a solvent, either organic or aqueous. Also, acids or alkalis are sometimes used to precipitate other materials from solution. If these extraneous materials used for separation can be recycled with a high efficiency, there is not a major problem. Sometimes, however, they cannot. If this is the case, then waste is created by discharge of that material. To reduce this waste, alternative methods of separation are needed, such as use of evaporation instead of precipitation. 

Benedict solution Aqueous solution of Na2C03, CuSO, and sodium citrate used for testing for reducing agents, particularly sugars, which give red-yellow colours or precipitates. 

CH2CI-CO-CH3. Colourless lachrymatory liquid b.p. 119°C. Manufactured by treating propanone with bleaching powder or chlorine. It is used as a tear gas and is usually mixed with the more potent bromoacetone. chloro acids Complex chloroanions are formed by most elements of the periodic table by solution of oxides or chlorides in concentrated hydrochloric acid. Potassium salts are precipitated from solution when potassium chloride is added to a solution of the chloro acid, the free acids are generally unstable. 

Dow process The process for the extraction of magnesium from sea-water by precipitation of Mg(OH)2 by Ca(OH)2 followed by solution of the hydroxide in hydrochloric acid. 

Mercury [) iodide, HgiL- pale green, is precipitated from a solution of a Hg2 salt by I". 

Nessler s reagent An alkaline solution of Hglj in KI used for detecting and estimating ammonia (brown colour or precipitate formed). 

By analogy, ammonium salts should behave as acids in liquid ammonia, since they produce the cation NH4 (the solvo-cation ), and soluble inorganic amides (for example KNHj, ionic) should act as bases. This idea is borne out by experiment ammonium salts in liquid ammonia react with certain metals and hydrogen is given off. The neutralisation of an ionic amide solution by a solution of an ammonium salt in liquid ammonia can be carried out and followed by an indicator or by the change in the potential of an electrode, just like the reaction of sodium hydroxide with hydrochloric acid in water. The only notable difference is that the salt formed in liquid ammonia is usually insoluble and therefore precipitates. 

The larger cations of Group 1 (K, Rb, Cs) can be precipitated from aqueous solution as white solids by addition of the reagent sodium tetraphenylborate, NaB(C( H5)4. Sodium can be precipitated as the yellow sodium zinc uranium oxide ethanoate (sodium zinc uranyl acetate). NaZn(U02)3(CH3C00)y. 9H2O. by adding a clear solution of zinc uranyl acetate in dilute ethanoic acid to a solution of a sodium salt. 

A white gelatinous precipitate of aluminium hydroxide is obtained when an alkali is added to an aqueous solution of an aluminium salt. Addition of an excess of caustic alkali causes the precipitate to redissolve, the whole process being reversed by the addition of a strong acid the actual substance present at any time depending on... 

Addition of ammonium hydroxide to a solution of an aluminium salt gives a white gelatinous precipitate of aluminium hydroxide, Al(OH)3, insoluble in excess. Sodium hydroxide gives the same precipitate, but in this case, it does dissolve in excess. 

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