Acid-alkali indicators

The history of acid-alkali indicators from the time of Robert Boyle to the present has been reviewed in an article that also discusses test papers and biological stains.55... 

It is also plain from his ample citations that Plot saw himself as part of a great Oxford chemical tradition, mentioning as he does Hooke, Mayow, Willis, and the Honorable Robert Boyle Esq. the Glory of his Nation and Pride of his Family , who had, in his own study of Oxfordshire waters, used Syrup of Violets as an early acid-alkali indicator. Then in November 1689, upon marrying, Robert Plot retired from the Chemistry Chair and left Oxford. He was succeeded to the post by Sir Edward Hannes, a medical man, who like so many seventeenth-century Oxford scientists (and most notably Robert Hooke) had followed the road from Westminster School to Christ Church. ... 

Boyle produced hydrogen by dissolving iron in dilute sulphuric or hydrochloric acid. He collected the gas in an inverted glass vessel and noted its inflammability. He made important contributions to qualitative analysis. In his Experimental History of Colours (1665) he described many colour reagents and acid-alkali indicators. 

Coloured salts loith alkalis. Dissolve a few crystals of o-nitro-phenol in a few ml. of 10% NaOH solution. An orange-coloured solution is produced, and becomes almost colourless on the addition of acids. Alkali restores the orange coloration, and so the solution exhibits the properties of an indicator. 

Other sources of hazard arise from the handling of such chemicals as concentrated acids, alkalis, metallic sodium and bromine, and in working with such extremely poisonous substances as sodium and potassium cyanides. The special precautions to be observed will be indicated, where necessary, in the experiments in which the substances are employed, and will also be supplied by the demonstrator. The exercise of obvious precautions and cautious handling will in most cases reduce the danger to almost negligible proportions. Thus, if concentrated sulphuric acid should be accidentally spilled, it should be immediately washed with a liberal quantity of water or of a solution of a mild alkali. 

That examples of glass and glazes manufactured many centuries ago still exist is an indication of the good resistance of such ceramics to abrasion, acids, alkalis, atmosphere, etc. 

Humic acid precipitates at salt concentrations >0.05 M and pH <4, while the fulvic acids are still soluble. Thus, humic acid is hardly ever found in salt water ( O.S M). Titration experiments with alkali indicate that there are consecutive steps of deprotoni-zation. A typical average pka-value would be 7 (26), and for a selected humic acid values of 4 and 9 are given for pk and pk, (27, 28). 31 aZ... 

The electrochemical oxidation of aromatic aldehydes (1) must be studied in strongly alkaline media. Acidity functions for strongly alkaline aqueous solutions of alkali metal and quaternary ammonium hydroxides, corresponding to dissociation of proton (H ), are well established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators for establishment of such scales, but whether an acidity scale based on one type of indicator can be rigorously applied to acid-base equilibria involving structurally different acidic groups for reactions in strongly alkaline media remains questionable. For substituted anilines, behavior both parallel (7) and nonparallel (8) to the H scale based on indole derivatives has been reported. The limited solubility of anilines in aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative with more than one hydroxide ion, irreversible substitution reactions (9), and the possibility of hydroxide ion addition rather than... 

Homopolymers of simple alkyl and aryl isocyanides (Mv.p.osm > 1000-4000) are insoluble in all common solvents. This statement, however, requires elaboration of the fact that trichloroacetic acid successfully disperses these polymers. Observations with poly(cr-toluyl isocyanide) are informative, since the polymer is canary yellow in color, and turns to dark brown in trichloroacetic acid—acting in the manner of an acid-base indicator dye. Dilution with water of the trichloroacetic acid solution of poly(aqueous alkali produces the original yellow color. It appears that the polyisocyanide is dispersed in trichloroacetic acid as a pro-tonated species. Conductimetric experiments on poly(a-phenylethyl isocyanide) in dichloroacetic acid confirm this view (25). 

The monoxide has been variously described, according to the method of preparation, as a black powder, or glistening crystals, or beautiful black cubes. Its density varies from 6 3 to 6-7, and it is a good conductor of electricity. On being heated in air it oxidises readily to the pentoxide with considerable evolution of heat. It dissolves in hydrofluoric acid and hydrochloric acid with evolution of hydrogen, and a pentavalent niobium salt is formed in solution. It is also dissolved by boiling potassium hydroxide to form potassium niobate. This behaviour of niobium monoxide towards acids and alkali indicates that divalent salts of niobium are too unstable to exist. A divalent chloride of tantalum has, however, recently been isolated (see p. 192). 

Infrared spectral studies of pyridine adsorbed on alkali metal ion-exchanged faujasites have demonstrated the absence of Brpnsted acidity, as reported by Eberly (151), Ignat eva et al. (208), and Ward (156, 209-211). Pyridine is adsorbed weakly by coordination to the alkali metal ions (151, 156). Addition of small amounts of water does not result in formation of Br0nsted acid sites, indicating that the coordinate bound pyridine is not associated with Lewis acid sites in the zeolite framework (210). 

The use of sulfur mustard as a vesicant CW agent implies that proteins of the skin are a primary target. It was found that upon exposure of human callus to [14C]sulfur mustard, a significant part of the radioactivity was covalently bound to keratin (30). Most of the radioactivity (80%) bound to keratin could be removed by treatment with alkali, indicating the presence of adducts to glutamic and/or aspartic acid residues. 

Metabolic Transit of Lysinoalanine. Urinary and Fecal Excretion of Protein-Bound Lysinoalanine (113). Three different alkali-treated proteins (lactalbumin, fish protein isolate, and soya protein isolate) containing, respectively, 1.79, 0.38, and 0.14 g of lysinoalanine/16 g nitrogen were given to rats and the urines and feces were collected. Lysinoalanine was measured before and after acid hydrolysis. The fecal excretion varied from 33 to 51% of the total ingested lysinoalanine and the urinary excretion varied from 10 to 25%. The higher level of lysinoalanine found after acid hydrolysis indicates that a certain quantity is excreted in the urines as combined lysinoalanine (see Table VII). The total recovery was inferior to the ingested quantity (50 to 71%) indicating that the molecule is transformed or retained in the body of the rat. 

Certain of the following test solutions are intended for use as acid-base indicators in volumetric analyses. Such solutions should be adjusted so that when 0.15 mL of the indicator solution is added to 25 mL of carbon dioxide-free water, 0.25 mL of 0.02 N acid or alkali, respectively, will produce the characteristic color change. 

Anal3Ttical and Synthetical Study of Proteins.—Fischer attacked the problem of the constitution of proteins from the synthetic side. Assuming that proteins consist of units of amino acids, as indicated by the analytical study of their hydrolytic products, he attempted to synthesize, from amino acids, compounds of similar complexity to the proteins. As already stated (p. 386), he found that the double anhydrides, resulting from the esters of amino acids by the loss of two molecules of alcohol from two molecules of the ester, took up one molecule of water when treated with dilute alkali and a single anhydride was obtained. The reactions may be represented as follows ... 

Stock solutions of DFP can be conveniently prepared in isopropanol in concentrations from 0.1 M to 0.001 M. These solutions are stable for a month in the refrigerator (Jansen et al. 1949). Moon et al. (1965), in their studies of the reaction of chymotrypsin with DFP, have determined the normality of stock solution of DFP in the following manner. Roughly 0.03 moles of DFP were added to an aqueous solution of 0.17 moles of KOH in a volumetric flask. The solution was allowed to stand for 12 hr at 25°C to permit complete hydrolysis, and was titrated to pH 7.0 with 0.1 N HCl. Identical titrimetric results were obtained after 43 hr standing in alkali indicating that complete hydrolysis had taken place after 12 hr. To determine the amount of free acid, if any, in the DFP, the same amount of DFP that was used... 

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