Weak acids naturally occurring

J. Kendall, J. E. Booze, and J. C. Andrews 3 have shown that the formation of hydrates, in the sense of water of crystallization, with the weak acids very seldom occurs, and when hydrates are formed, the acid has the amphoteric character of a phenol. There is also a regular increase in the tendency of an acid to form hydrates, as the strength of the acid increases, until, with the strong acids, well-defined stable hydrates appear. The complexity and stability of the hydrates increase with the strength of the acid. These facts are in harmony with the weak acid nature of water. 

Lipids differ from the other classes of naturally occurring biomolecules (carbohy drates proteins and nucleic acids) in that they are more soluble m nonpolar to weakly polar solvents (diethyl ether hexane dichloromethane) than they are m water They include a variety of structural types a collection of which is introduced m this chapter... 

Effect on Oxide—Water Interfaces. The adsorption (qv) of ions at clay mineral and rock surfaces is an important step in natural and industrial processes. SiUcates are adsorbed on oxides to a far greater extent than would be predicted from their concentrations (66). This adsorption maximum at a given pH value is independent of ionic strength, and maximum adsorption occurs at a pH value near the piC of orthosiUcate. The pH values of maximum adsorption of weak acid anions and the piC values of their conjugate acids are correlated. This indicates that the presence of both the acid and its conjugate base is required for adsorption. The adsorption of sihcate species is far greater at lower pH than simple acid—base equihbria would predict. 

With very few exceptions, naturally occurring acids and alkalies are weak. All acids known in antiquity were of organic origin some occur in fruits, especially in unripe fruitjuices. Most ancient alkalies were derived from the ash of plants such as barilla, Salsola soda and Salsola kali (Russian thistle), and kelp. 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

The system above describes the addition of alkali to a lake containing a weak acid. The reverse process also occurs, with acid being added to a base, e.g. when the tributary rivers deliver acid rain to a lake and the lake basin is made of limestone or chalk. In such a case, the lake pH drops as the acid rain from the rivers depletes the amounts of natural Ca(OH)2 dissolved in the lake. 

Hydrogen cyanide (HCN) is a colorless, highly poisonous gas or liquid (below 26.7 °C) having an odor of bitter almonds (Hartung 1994 Pesce 1994). It is a weak acid. Exposures may occur in industrial situations as well as from cigarette smoke and combustion products and from naturally occurring cyanide compounds in foods. There is a potential for exposure when any acid is mixed with a cyanide salt. Intravenously administered sodium nitroprusside (Na2[Fe(CN)5N0]-2H20) has been used clinically to lower blood pressure (Schulz et al. 1982). Chemical and physical properties are listed in Table 5-2. 

Caproic acid, C5H11COOH, occurs naturally in coconut and palm oil. It is a weak monoprotic acid, with = 1.3 x 10 . A certain aqueous solution of caproic acid has a pH of 2.94. How much acid was dissolved to make 100 mL of this solution ... 

O Oxalic acid, HOOCCOOH, is a weak diprotic acid that occurs naturally in some foods, including rhubarb. Calculate the pH of a solution of oxalic acid that is prepared by dissolving 2.5 g in 1.0 L of water. What is the concentration of hydrogen oxalate, HOOCCOO , in the solution ... 

Acidification of these nitronic acid salts may lead to a variety of products depending upon the nature and strength of the acid employed. Weak acids, such as acetic or carbonic acids, simply regenerate the nitro-paraffin. Warm, concentrated mineral acids hydrolyze the salts of primary aci-nitroparaffins to produce fatty acids and salts of hydroxyl-amine. This is in reality a reaction of the nitronic acids and occurs when the primary nitroparaffins themselves are warmed with concentrated mineral acid.17... 

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