Solutions and Precipitates

Aqueous solutions of ionic compounds contain dissolved positive, and negative ions. When two such solutions are mixed, the ions may take part in a double-replacement reaction. One outcome of a double-replacement reaction is the formation of a precipitate. By writing ionic equations and knowing the solubilities of specific ionic compounds, you can predict whether a precipitate will be formed. 

Can you predict whether two aqueous solutions wil form a precipitate when they are mixed  

Always wear safety goggles, gloves, and a lab apron. Use extra care when handling the solutions. 

Do not dispose of wastes in the sink or trash can. Never place the pipette in your mouth. 

What are the three types of products that can form from double-replacement reactions  

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Amino-3 5-diiodobenzoic acid. In a 2 litre beaker, provided with a mechanical stirrer, dissolve 10 g. of pure p-aminobenzoic acid, m.p. 192° (Section IX,5) in 450 ml. of warm (75°) 12 -5 per cent, hydrochloric acid. Add a solution of 48 g. of iodine monochloride (1) in 40 ml. of 25 per cent, hydrochloric acid and stir the mixture for one minute during this time a yellow precipitate commences to appear. Dilute the reaction mixtiue with 1 litre of water whereupon a copious precipitate is deposited. Raise the temperature of the well-stirred mixture gradually and maintain it at 90° for 15 minutes. Allow to cool to room tempera-tiue, filter, wash thoroughly with water and dry in the air the yield of crude acid is 24 g. Purify the product by dissolving it in dilute sodium hydroxide solution and precipitate with dilute hydrochloric acid the yield of air-dried 4-amino-3 5-diiodobenzoic acid, m.p. >350°, is 23 g. 

Acids that are solids can be purified in this way, except that distillation is replaced by repeated crystallisation (preferable from at least two different solvents such as water, alcohol or aqueous alcohol, toluene, toluene/petroleum ether or acetic acid.) Water-insoluble acids can be partially purified by dissolution in N sodium hydroxide solution and precipitation with dilute mineral acid. If the acid is required to be free from sodium ions, then it is better to dissolve the acid in hot N ammonia, heat to ca 80°, adding slightly more than an equal volume of N formic acid and allowing to cool slowly for crystallisation. Any ammonia, formic acid or ammonium formate that adhere to the acid are removed when the acid is dried in a vacuum — they are volatile. The separation and purification of naturally occurring fatty acids, based on distillation, salt solubility and low temperature crystallisation, are described by K.S.Markley (Ed.), Fatty Acids, 2nd Edn, part 3, Chap. 20, Interscience, New York, 1964. 

The mixture of diastereomers has been separated into its two principal components by Izatt, Haymore, Bradshaw and Christensen who had previously identified the two principal diastereomers as the cis-syn-cis and cis-anti-cis isomers. Their previous separation technique involved a protracted chromatography on alumina but the new method relied upon the difference in water solubility between the lead perchlorate and hydroniur perchlorate complexes. The lead perchlorate complex is essentially insoluble in aqueous solution and precipitates from it. Using this method, one may obtain 39% of the high-melting polymorph (mp 83—84°) and 44% of the low-melting compound (mp 62—63°). Note that the former also exists in a second crystalline form, mp 69—70°. 

A solution of 2o, 3o, 16o, 17o -diepoxy-17/3-acetoxy-5o -androstane (25 grams), prepared from 3,17-diacetoxy-5o -androstane-2,16-diene Chem. Abs. 1960, 54, 8908) by treatment with m-chlor-per-benzoic acid, in piperidine (120 ml) and water (40 ml) was boiled under reflux for 5 days, the solution was concentrated and the product precipitated by the addition of water. The solid was collected, dissolved in dilute hydrochloric acid, filtered to give a clear solution and precipitated by the addition of sodium hydroxide soiution. Crystalliza-... 

The mixture is then flushed with nitrogen to expel excess chlorine. During this process the product crystallizes from the solution and precipitation is completed by cooling the reaction mixture to 20°. The mixture is filtered and the product is washed with 1 1. of water, and air dried to yield 112 g. (77%) of 2,3-dichloro-2,5-di-[Pg.33]

If heated in glycerol,7-9 or ethylene glycol, or even in water solution and precipitated from these solutions by alcohol, inulin separates in a form soluble in cold water. This soluble form is also produced by the action of carbon dioxide.10... 

The amine (B) is a proprietary mixture of C8 and C10 primary alkylamines dissolved in kerosene. The uranium is stripped from the organic solution with an alkaline stripping solution and precipitated as ammonium diuranate. See also Dapex. 

Dual Alkali A flue-gas desulfurization process. The sulfur dioxide is absorbed in aqueous sodium hydroxide and partially oxidized, and this liquor is then treated with calcium hydroxide to regenerate the scrubbing solution and precipitate calcium sulfate. Developed by Combustion Equipment Associates and Arthur D. Little. 

Dissolve the sample in NaOH solution and precipitate ZnS with NaS solution. Dissolve ZnS in HC1 solution, add ammonium citrate to mask A1 and then titrate Zn at pH = 9 using eriochrome black T as indicator. 

In precipitation studies (4 7, 4 ) it has been shown that, below a certain Mg/Ca concentration ratio in the aqueous solution, the rate of nucleation of calcite was faster than that of aragonite. Above that Mg/Ca ratio the order was reversed. This was explained by the effect of Mg2+ ions on the interfacial tension between the solution and precipitate, which apparently is larger for calcite than for aragonite (49). At still higher Mg/Ca ratios dolomite can be formed (50). Such low temperature precipitates of dolomite contain ordering defects. The number of defects increases when precipitation proceeds in a shorter time interval or at lower temperatures C51 ). 

Solutions and precipitates were analyzed on a Beckman Spectra-Span VI direct current plasma emission spectrophotometer (DCP), Precision for the Ca2 + analyses was 3% and for the Ba2 + 2% except for the most dilute samples In which It rose as high as 5%. Calcite mineralogy was determined on a Philips x-ray diffractometer calcite was the only phase recorded except In speed runs of under one hour In duration (not Included In this study) which produced vaterite. Details of analytic procedures are available In Pingitore and Eastman (30,31). 

Highly reactive calcium can be readily prepared by the reduction of calcium halides in tetrahydrofuran solution with preformed lithium biphenylide under an argon atmosphere at room temperature.5 This colored calcium species seems to be reasonably soluble in THF. However, the reactive calcium complex prepared from preformed lithium naphthalenide was insoluble in THF solution and precipitated out of solution to give a highly reactive black solid. The exact nature of this black calcium complex has not been determined. Acid hydrolysis of the black material releases naphthalene as well as THF. Accordingly, the most likely structure of the black material is a Ca-naphthalene-THF complex similar in nature to the soluble magnesium-anthracene complex recently reported.6... 

Elemental composition Be 8.58%, S 30.51%, 0 60.91%. The metal may he analyzed hy various instrumental techniques (see Berylhum). Sulfate may he measured in the aqueous solution of the salt hy gravimetric method (adding BaCh solution and precipitating BaS04) or hy ion chromatography. 

Metal catalytic activity may be expected to be a function of the solubility of the active species and/or the ease of electron transfer to the catalyst. The results given in Table IV show conclusively that the suggestion that catalysis occurs at a gas-solid interface (13) does not hold in these systems. Preliminary experiments showed that copper ion- and haemin-catalyzed systems oxidized rapidly with no trace of solid precipitation, and that cobalt and nickel catalysis were characterized by the production of colored solutions and precipitates. Filtration experiments showed these precipitates played only a small part in catalysis (Table IV). 

Secondary phases predicted by thermochemical models may not form in weathered ash materials due to kinetic constraints or non-equilibrium conditions. It is therefore incorrect to assume that equilibrium concentrations of elements predicted by geochemical models always represent maximum leachate concentrations that will be generated from the wastes, as stated by Rai et al. (1987a, b 1988) and often repeated by other authors. In weathering systems, kinetic constraints commonly prevent the precipitation of the most stable solid phase for many elements, leading to increasing concentrations of these elements in natural solutions and precipitation of metastable amorphous phases. Over time, the metastable phases convert to thermodynamically stable phases by a process explained by the Guy-Lussac-Ostwald (GLO) step rule, also known as Ostwald ripening (Steefel Van Cappellen 1990). The importance of time (i.e., kinetics) is often overlooked due to a lack of kinetic data for mineral dissolution/... 

The solution and precipitate were separated by filtration. Qualitative analysis of the precipitate showed that it contained cerium(III) and sulfate ion. [No precipitate appeared when m-bisoxalatodiaquochromate(111) ion and cerium(IV) were allowed to react at this acidity under conditions where the sulfate and/or cerium concentrations were somewhat lower.] The filtrate, including washings, was diluted to a measured volume, and two measured aliquots of this solution were withdrawn for study. The first aliquot was passed onto a cation exchange column in the hydrogen form. Elution with 1M sulfuric acid left a small dark violet band of hexaaquochromium(III) ion at the top of the column, while the rest of the chromium passed through the column. [In separate experiments it was confirmed that the Cr(OH2)fe+3 ion is retained as a dark violet band at the top of the resin when the resin is eluted with 1M sulfuric acid. This is in agreement with the observations of King and Dismukes (23).] Analysis of the effluent solution showed that 4 to 5% of the chromium had been retained by the column. 

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