Identification Tests Potassium

In the known absence of bromoform, iodoform, chloral, and other halogenated methanes, the formation of phenyhsonitrile with aniline provides a simple and faidy sensitive but nonspecific test for the presence of chloroform, the carbylamine test. Phenyhsonitrile formation is the identification test given in the British Pharmacopoeia. A small quantity of resorcinol and caustic soda solution (10% concentration) added to chloroform results in the appearance of a yellowish red color, fluorescing yeUow-green. When 0.5 mL of a 5% thymol solution is boiled with a drop of chloroform and a small quantity of potassium hydroxide solution, a yellow color with a reddish sheen develops the addition of sulfuric acid causes a change to brilliant violet, which, diluted with water, finally changes to blue (33). 

Aconitine produces an intense tingling sensation when a drop of a solution, 1 in 10,000, is applied to the tip of the tongue. It also gives a characteristic unstable, crystalline precipitate when a few drops of potassium permanganate solution are added to a solution of the alkaloid in dilute acetic acid. The formation of acetic acid when the alkaloid is heated dry, or of benzoic acid when it is hydrolysed by alkali, have also been suggested as identification tests. For the recognition of minute quantities a biological test is probably the best procedure. ... 

The British Pharmacopoeia describes another identification test [32]. To 0.2 mL of a 10 % w/v solution, one adds 2 mL of water and 0.5 mL of 1 M sulfuric acid. The mixture is shaken, and then 1 mL of a 0.1 % w/v solution of potassium permanganate is added. A positive reaction is where the color is immediately discharged. 

B. Add 200 mg of potassium chloride to 50 mL of the solution or gel obtained in Identification Test A, then reheat, mix well, and cool. A short-textured ( brittle ) gel forms. 

A. Mix 500 mg of sample with 2.5 g of anhydrous potassium carbonate, and heat the mixture in a platinum or nickel cmcible until it melts completely. Cool, add 5 mL of water, and allow to stand for 3 min. Heat the bottom of the cmcible gently, detach the melt, and transfer it into a beaker with the aid of about 50 mL of water. Gradually add hydrochloric acid until no effervescence is observed, add 10 mL more of the acid, and evaporate to dryness on a steam bath. Cool, add 20 mL of water, boil, and filter through ash-free filter paper. An insoluble residue of silica remains. Retain the filtrate for Identification Test B. 

Aluminum Identification Test, 753 Aluminum Magnesium Silicate, 41 Aluminum Potassium Sulfate, 21 Aluminum Sodium Sulfate, 21 Aluminum Sulfate, 22 Ambrette Seed Liquid, 23 Ambrette Seed Oil, 23, 596 Aminoacetic Acid, 186 A-[4-[[(2-Amino-l,4-dihydro-4-oxo-6-pteridinyl)methyl] amino] benzoyl] -l-glutamic Acid, 157 3 - Amino-7-dimethylamino-2-methylphenazine Chloride, 861 L-2-Aminoglutaramic Acid, 175 L-2-Amino-5-guanidinovaleric Acid, 32, (S3)5... 

The scheme that is shown in Figure 9.9 is very simple. More complex qualitative analyses involve many more steps of isolation and identification, including some steps that are not precipitation reactions. For example, some ions, such as sodium, Na", and potassium, K, cannot he precipitated out of an aqueous solution, because the ionic compounds that contain them are always soluble. Instead, chemists identify these ions using a flame test. In the following ThoughtLab, you will simulate a qualitative analysis that includes a flame test. 

Carboxylic acids often have been identified by means of paper chromatography Clarke and Bazill (10) have extracted plasticizers from polyvinyl chloride first with ether and then with methanol. Subsequently the extracts were saponified with alcoholic potassium hydroxide, and the precipitated potassium salts were isolated and converted into free acids. These, in alcoholic solution, were then applied to paper and chromatographed ascendingly with a mixture of butanol, pyridine, water, and ammonia the migration period was about six hours. A number of additional color tests facilitated identification of unknown acids. 

Identification A 1 20 aqueous solution gives positive tests for Aluminum, for Potassium, and for Sulfate, Appendix IIIA. Assay Not less than 99.5% and not more than 100.5% of A1K(S04)2-12H20. 

Identification An infrared absorption spectrum of a potassium bromide dispersion of Aspartame-Acesulfame Salt exhibits maxima only at the same wavelengths as those of a typical spectrum as shown in the section on Infrared Spectra, using the same test conditions as specified therein. 

Identification Cautiously dissolve 250 mg of sample in 5 mL of glacial acetic acid, and add a few drops of a saturated solution of potassium iodide. Iodine is liberated. Add 20 mL of water and sufficient sodium thiosulfate TS to remove the iodine color. The resulting solution gives positive tests for Calcium, Appendix IIIA. 

Identification A 1 5 aqueous solution responds to the flame test for Potassium and gives positive tests for Benzoate, Appendix IIIA. 

Identification A 1 10 aqueous solution gives positive tests for Potassium and for Bicarbonate, Appendix IIIA. 

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