Precipitation, acid

We have only recently understood the phenomena that control rainwater pH in the natural, unpolluted environment. As pointed out in Section 16.2, these appear to be mainly the cycles of sulfur and nitrogen compounds. A model of the unperturbed system is necessary in order to understand and predict the changes that occur when strong sulfur- and nitrogen-acids are 

When fossil fuels such as coal and oil are burned, a variety of 

Properties of Basic Soiutions Most soaps are bases, so if you think about how soap feels, you can figure out some of the properties of basic solutions. Basic solutions feel slippery. Acids in water solution taste sour, but bases taste bitter— as you know if you have ever accidentally gotten soap in your mouth. 

Like acids, bases are corrosive. Bases can cause burns and damage tissue. You should never touch or taste a substance to find out whether it is a base. Basic solutions contain ions and can conduct electricity. Basic solutions are not as reactive with metals as acidic solutions are. 

Chalk and oven cleaner are examples of familiar products that contain bases. Your blood is a basic solution. Calcium hydroxide, often called lime, is used to mark the lines on athletic fields. It also can be used to treat lawns and gardens that have acidic soil. 

Sodium hydroxide, known as lye, is a strong base that can cause burns and other health problems. Lye is used to make soap, clean ovens, and unclog drains. 

---

The benzoic acid may be separated by steam distillation or by saturating the aqueous mixture of sodium salts with sulphur dioxide whilst maintaining the temperature below 40° the benzoic acid precipitates and can be separated by filtration or extraction with ether. Acidification of the filtrate with hydrochloric acid liberates the pyruvic acid. The pjTuvic acid may be oxidised < lth hydrogen peroxide to the arylacetic acid, for example ... 

Because of the mixture of VOCs in the atmosphere, the composition of smog reaction products and intermediates is extremely complex. formed via reaction 16, is important because when dissolved in cloud droplets it is an important oxidant, responsible for oxidising SO2 to sulfuric acid [7664-93-9] H2SO4, the primary cause of acid precipitation. The oxidation of many VOCs produces acetyl radicals, CH CO, which can react with O2 to produce peroxyacetyl radicals, CH2(C0)02, which react with NO2... 

D. Albritton and co-workers, NAPAPIntenm Assessment, Vol. 3 (Atmosphere Process and Deposition), National Acid Precipitation Assessment Program, Washiagton, D.C., 1987. 

The viscosity of algiaate solutioas is iadepeadeat of pH ia the range 5—10, but below pH 4.5, the viscosity iacreases uatil the pH reaches 3 whea iasoluble alginic acid precipitates. Propyleae glycol algiaate is soluble and stable at pH 2—3 but not above 6.5. 

The significance of phenoxy anions is well recognized in the isolation of kraft and other water-insoluble technical lignins by acid precipitation. The ioniza tion of phenoHc hydroxyl groups coupled with the reduction of molecular size renders native lignin soluble in the aqueous pulping solution, thus enabling its separation from the polysaccharide components of wood. 

Many analytical methods depend on the conversion of the tellurium in the sample to teUurous acid, H2Te02. Should teUurous acid precipitate on dilution, it can be redissolved with hydrochloric acid. Although tellurium is not as readily volatile as selenium, precautions should be taken to prevent the volatilisation of tellurium when halogen or hydrohaUde media are used during sample decomposition. 

Polytungsta.tes, An important and characteristic feature of the tungstate ion is its abiUty to form condensed complex ions of isopolytungstates in acid solution (38). As the acidity increases, the molecular weight of the isopolyanions increases until tungstic acid precipitates. However, the extensive investigations on these systems have been hampered by lack of weU-defined soHd derivatives. 

DAG is treated with ethanol and hydrochloric acid in the presence of inert solvent, eg, chlorinated solvents, hydrocarbons, ketones, etc. The L-ascorbic acid precipitates from the mixture as it forms, minimising its decomposition (69). Cmde L-ascorbic acid is isolated through filtration and purified by recrystallization from water. The pure L-ascorbic acid is isolated, washed with ethanol, and dried. The mother Hquor from the recrystallization step is treated in the usual manner to recover the L-ascorbic acid and ethanol contained in it. The cmde L-ascorbic acid mother Hquor contains solvents and acetone Hberated in the DAG hydrolysis. The solvents are recovered by fractional distillation and recycled. Many solvent systems have been reported for the acid-catalyzed conversion of DAG to L-ascorbic acid (46). Rearrangement solvent systems are used which contain only the necessary amount of water required to give >80% yields of high purity cmde L-ascorbic acid (70). 

R. A. Smith and R. B. Alexander, Evidencefor Acid-Precipitation Induced Trends in Stream Chemistry at Hydrologic Bench-Mark Stations, E.S. Geological Survey... 

National Acid Precipitation Assessment Piogiam (NAPAP), 1992 Keport to Congress NAPAP, Washington, D.C., 1992. 

Some products are precipitated from the fermentation broth. The insoluble calcium salts of some organic acids precipitate and are col-lec ted, and adding sulfuric acid regenerates the acid while forming gypsum (calcium sulfate) that constitutes a disposal problem. An early process for recovering the antibiotic cycloserine added silver nitrate to the fermentation broth to precipitate an insoluble silver salt. This process was soon obsolete because of poor economics and because the silver salt, when diy, exploded easily. 

Acidic Precipitation," Vols. 1-5. Advances in Environmental Sciences, Springer-Verlag, London, 1989-90. 

Interagency Task Force on Acid Precipitation. National Add Predpitation Assessment Plan. NTIS, PB82-244 617, 1982. 

The primary constituents to be measured are the pH of precipitation, sulfates, nitrates, ammonia, chloride ions, metal ions, phosphates, and specific conductivity. The pH measurements help to establish reliable longterm trends in patterns of acidic precipitation. The sulfate and nitrate information is related to anthropogenic sources where possible. The measurements of chloride ions, metal ions, and phosphates are related to sea spray and wind-blown dust sources. Specific conductivity is related to the level of dissolved salts in precipitation. 

The autoclave is cooled to room temperature, and the carbon dioxide is bled off. The solid reaction product is taken from the autoclave, pulverized, and dissolved in 1 1. of water at 50-60°. Ten grams of decolorizing carbon is added, and the mixture is stirred well and filtered to remove cadmium salts and carbon. The filtrate is heated to 80-90° and acidified with concentrated hydrochloric acid to pH 1 (Note 5). 2,6-Naphthalenedicar-boxylic acid precipitates. It is separated from the hot mixture by filtration. It is then suspended in 500 ml. of water at 90-95° (Note 5), separated by filtration, and washed successively with 300 ml. of water, 300 ml. of 50% ethanol, and 300 ml. of 90% ethanol. After being dried at 100-150°/150 mm. in a vacuum oven, the 2,6-naphthalenedicarboxylic acid weighs 42-45 g. (57-61%). It decomposes on a heated block at 310-313°. 

The advantages of m-chloroperbenzoic acid have already been emphasized it is commercially available, stable and highly selective when methylene dichloride is used as solvent, the m-chlorobenzoic acid precipitates from solution, thereby decreasing the danger of acid-catalyzed side reactions." ... 

Franck, R., David, R., Villenuaux, J. and Klein, J.P., 1988. Crystallization and precipitation engineering - II. A chemical reaction engineering approach to salicylic acid precipitation Modelling of batch kinetics and application to continuous operation. Chemical Engineering Science, 43, 69-11. 

By cooling, the sodium salt of 3-n-butylamino-4-phenoxy-5-sulfamylbenzoic acid precipitated. It was filtered off and recrystallized from water (100 ml). The sodium salt, crystallizing with 3 molecules of water, was then dissolved in boiling water (200 ml), 1 N hydrochloric acid was added to pH 2.5, and after cooling the precipitated 3-n-butylamino-4-phenoxy-... 

To 1,400 ml of an approximately 50% water/triglycol solution of the potassium salt of cheno-deoxycholic acid, obtained by the Wolff-Kishner reduction (using hydrazine hydrate and potassium hydroxide) from 50 g of 7-acetyl-12-ketochenodeoxycholic acid, 220 ml of dilute hydrochloric acid is added to bring the pH to 2. The solution is stirred and the crude cheno-deoxycholic acid precipitates. The precipitate is recovered and dried to constant weight at about 60°C. About 36 g of the crude chenodeoxycholic acid, melting in the range of 126°-129°C, is obtained. 

The alkali-insoluble residue comprising ethyl p-cyclohexyloxybenzoate is hydrolyzed by refluxing with 10% sodium hydroxide solution for about 3 hours. The alkaline reaction mixture is acidified with hydrochloric acid whereupon p-cyclohexyloxybenzoic acid precipitates. The precipitate is separated by filtration, washed with water and dried. It melts at about 178° to 180°C. Yield about 7%. 

To the chlorobenzene solution is then added sodium hydroxide dissolved in water and the chlorobenzene is removed by a steam distillation. After all of the chlorobenzene is removed, the precipitate which forms during the distillation is removed by filtration and discarded. The solution is cooled and acidified with hydrochloric acid, precipitating a tan solid. This is removed by filtration and washed acid-free. It Is then treated with sodium bicarbonate solution to remove any acid present and is then washed with water to remove all traces of bicarbonate. After drying approximately a 75% yield of mexenone is obtained. 

---