Precipitation reactions fractional

Lee and Bethke (1996) presented an alternative technique, also based on mass balance equations, in which the reaction modeler can segregate minerals from isotopic exchange. By segregating the minerals, the model traces the effects of the isotope fractionation that would result from dissolution and precipitation reactions alone. Not unexpectedly, segregated models differ broadly in their results from reaction models that assume isotopic equilibrium. 

When butadiene was polymerized in the presence of a PVC suspension in chlorobenzene using a catalyst system based on Et2AlCl, the methanol-precipitated reaction product had little or no solubility in refluxing hexane. The soluble fraction, when obtainable, was identifiable as a greater than 90% cw-1,4-polybutadiene. In this case, the hexane-insoluble residue was essentially completely soluble in tetrahydrofuran, probably owing to the low molecular weight of the polybutadiene in the PVC-cw-1,4-polybutadiene reaction product. 

Classical methods of separation [7] are (1) fractional crystallization, (2) precipitation and (3) thermal reactions. Fractional crystallization is an effective method for lanthanides at the lower end of the series, which differ in cation radius to a large extent. The separation of lanthanum as a double nitrate, La(N03)3-2NH4N03-4H20, from praseodymium and other trivalent lanthanide with prior removal of cerium as Ce4+ is quite a rapid process and is of commercial significance. Other examples are separation of yttrium earths as bromates, RE(Br03>9H20 and use of simple nitrates, sulfates and double sulfate and alkali metal rare earth ethylenediamine tetraacetate complex salts in fractional crystallization separation. 

Moreover, a solute B satisfying the condition e < 0 can cause precipitation of an oxide B203 by reaction with the excess oxygen in the alloy. The mole fraction of dissolved oxygen in equilibrium with the B203 precipitate (reaction (6.37)), denoted X , is given by ... 

In soils, F can be found in four major fractions (1) dissolved in soil solution (2) sorbed to Al, Fe, and Mn oxides and hydroxides and carbonates (3) solid phases, such as fluorite and fluorophlogopite and (4) associated with organic compounds. The solubility of F in soil solution is variable and is affected by pH, speciation, adsorption and desorption reactions, and dissolution and precipitation reactions (Luther et al., 1996). Acidic conditions and low calcium carbonate content are favorable to F solubility and can therefore enhance both root uptake (Weinstein and Alscher-Herman, 1982) and migration to surface and ground water (Smith, 1983). These conditions can lead to human, plant, and animal health issues. Soils that do contain appreciable amounts of calcium carbonate and are neutral to slightly alkaline conditions can fix F as insoluble calcium fluoride (CaF2), and reduce its bioavailability and mobility (Kubota et al., 1982 Tracy et al., 1984 Reddy et al., 1993 Poulsen and Dudas, 1998). 

Although we have considered many reactions so far, we have examined only a tiny fraction of the millions of possible chemical reactions. To make sense of all these reactions, we need some system for grouping reactions into classes. Although there are many different ways to do this, we will use the system most commonly used by practicing chemists. They divide reactions into the following groups precipitation reactions, acid-base reactions, and oxidation-reduction reactions. 

A crude cell-free extract of skeletal muscle contained 32 mg orotein/ml. Ten microliters of the extract catalyzed a reaction-aJL rate of. mole/min ) under standard optimum assay conditions, (gifty millilitei ot qhe extract were fractionated by ammonium sulfate precipitation. The fraction precipitating between 20% and 40% saturation was redissplved in 10 ml. This solution was found to contain 50 mg protein/ml. Ten microliters of this purified fraction catalyzed the reaction ata rate of 0 65 mole/min. Calculate (a) the percent recovery of the enzyme in the purified fraction, and (b) the degree of purification obtained by the fractionation (the purification factor). 

Fifty milliliters of the cell-free extract described above was fractionated by ammonium sulfate precipitation. The fraction precipitating between 30 and 50% saturation was redissolved in a total volume of 10 ml and dialyzed. The solution after dialysis occupied 12 ml and contained 30 mg protein/ml. Twenty microliters of the purified fraction catalyzed the phosphorylase reaction at a rate of 5.9 nmoles/min under the standard assay conditions. Calculate (a) the recovery of the enzyme and (b) the degree of purification obtained in the ammonium sulfate step. 

Principle The EDTA-plasma sample is applied onto the protective mesh. Integrated precipitation and lipoprotein fractionation by means of dextrane sulfate and magnesium ions then take place in the precipitation layer. The precipitated lipoprotein fractions - chylomicrones, VLDL (very low density lipoproteins) and LDL (low density lipoproteins) - are filtered by the transport layer and only the HDL (high-density lipoproteins) fraction reaches the indicator him where the HDL cholesterol concentration is determined enzymatically by the following reaction ... 

Experimental time-temperature-transformation (TXT) diagram for Ti-Mo. Xhe start and finish times of the isothermal precipitation reaction vary with temperature as a result of the temperature dependence of the nucleation and growth processes. Precipitation is complete, at any temperature, when the equilibrium fraction of a is established in accordance with the lever rule. Xhe solid horizontal line represents the athermal (or nonthermally activated) martensitic transformation that occurs when the p phase is quenched. 

Cations often interfere with each other in the final tests designed to detect the presence of specific cations. Therefore, cations must first be separated before identification can be accomplished. In fact, as with many chemical mixtures, separation of cations may be considerably more difficult than identification. Careful work is again very important if the separations are not clean, results in identification tests may be masked by interfering cations. Separation of a complex mixture of cations is by no means simple and is generally broken down into several parts. Each part involves a fairly small group of cations which can be isolated from the mixture on the basis of some property which is common to the ions in the group and then studied as a separate set. After isolation, the cations within a group are further resolved by means of a series of chemical reactions into soluble and insoluble fractions which are sufficient to allow identification of each cation by one or more tests specific to that ion once interferences have been removed. Various types of chemical reactions will be used for separations and identifications in this experiment precipitation reactions, acid-base reactions, complex ion formations, and oxidation-reduction reactions. 

A major fraction of sludge in most merchant-sludge acids is the compound (Fe,AI)3KHi4(P04)a 4H2O. It precipitates slowly over a period of several weeks therefore, long storage periods are required to ensure reasonable completion of the precipitation reaction. 

We have described the precipitation reactions that occur when solid AgN03 is added slowly to a solution that is 0.0010 M in Cl", Br", and I". Silver iodide begins to precipitate first 99.955% of the l precipitates before any sohd AgBr is formed. Silver bromide begins to precipitate next 99.82% of the Br" and 99.999917% of the 1 precipitate before any solid AgCl forms. This shows that we can separate these ions very effectively by fractional precipitation. 

Figure 1. SEC elution curves of the precipitated hemicellulose fraction from the Organocell process and a glucomannan, both from Norway spruce. SEC TSK HW 55 (100 X 2,5 cm) 1 ml/min 0,1 Mphosphate buffer pH 7.2 detection 540 nm after reaction with 0.2% 3,5 dihydroxytoluene in 72% HfS04.

A polysaccharide obtained from certain seaweeds which forms a gel when water is added. It is composed of at least two fractions, agaropectin and agarose. Agar gels are used in many immunochemical precipitation reactions and can also be used as an electrophoretic medium, although agarose is preferred for this particular purpose. 

Fit a 1500 ml. bolt-head flask with a reflux condenser and a thermometer. Place a solution of 125 g. of chloral hydrate in 225 ml. of warm water (50-60°) in the flask, add successively 77 g. of precipitated calcium carbonate, 1 ml. of amyl alcohol (to decrease the amount of frothing), and a solution of 5 g. of commercial sodium cyanide in 12 ml. of water. An exothermic reaction occurs. Heat the warm reaction mixture with a small flame so that it reaches 75° in about 10 minutes and then remove the flame. The temperature will continue to rise to 80-85° during 5-10 minutes and then falls at this point heat the mixture to boiling and reflux for 20 minutes. Cool the mixture in ice to 0-5°, acidify with 107-5 ml. of concentrated hydrochloric acid. Extract the acid with five 50 ml. portions of ether. Dry the combined ethereal extracts with 10 g. of anhydrous sodium or magnesium sulphate, remove the ether on a water bath, and distil the residue under reduced pressure using a Claiseii flask with fractionating side arm. Collect the dichloroacetic acid at 105-107°/26 mm. The yield is 85 g. 

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