Hydrogen sulphide, determination

Kupec et al. [180] determined total sulphur in sludge by a method involving magnesium reduction in which the sample is heated with magnesium powder to convert all sulphur compounds into magnesium sulphide. The magnesium sulphide is treated with sulphuric acid and the evolved hydrogen sulphide determined by iodometric titration. 

Samples should be taken from the ordinary hydrocast samplers immediately after the oxygen sample and in the the same manner as these samples (see Chapter 4). The hydrocast samplers should preferably be all-plastic, since sulphide reacts with many metals. When no oxygen is present in the water, samples for hydrogen sulphide determination should be taken first (see also Chapter 2). We use 50 mL oxygen bottles. Hydrogen sulphide is probably present in the water when the manganese hydroxide precipitate in the oxygen sample is completely white instead of brownish. 

Many other methods available for hydrogen sulphide determinations have not been applied in routine work. Potentiometric titration with HgQ2 (Bouligue, 1981) or gravimetric methods, e.g., precipitation of HgS (Dyrssen et al., 19%) should be avoided because of detrimental effects on the environment. In Sweden such methods are not allowed in environmental routine work and will probably be illegal in other EU countries. 

Composition - which describes the proportion of hydrocarbon components (C, - Cj+) (which determine the fluid properties), and how many non-hydrocarbon substances (e.g. nitrogen, carbon dioxide and hydrogen sulphide) are present. 

The procedure is illustrated by determination of the concentration of hydrogen sulphide water. 

Soluble sulphides. Hydrogen sulphide and soluble sulphides can also be determined by oxidation with potassium iodate in an alkaline medium. Mix 10.0 mL of the sulphide solution containing about 2.5 mg sulphide with 15.0 mL 0.025M potassium iodate (Section 10.126) and 10 mL of 10M sodium hydroxide. Boil gently for 10 minutes, cool, add 5 mL of 5 per cent potassium iodide solution and 20 mL of 4M sulphuric acid. Titrate the liberated iodine, which is equivalent... 

Antimony pyrogallate, Sb(C6H503). Antimony(III) salts in the presence of tartrate ions may be quantitatively predpitated with a large excess of aqueous pyrogallol as the dense antimony pyrogallate. The method fadlitates a simple separation from arsenic the latter element may be determined in the filtrate from the predpitation of antimony by direct treatment with hydrogen sulphide. 

Florin THJ. 1991. Hydrogen sulphide and total acid-volatile sulphide in feces, determined with a direct spectrophotometric method. Clin Chim Acta 196 127-134. 

As esters the alkyl halides are hydrolysed by alkalis to alcohols and salts of halogen acids. They are converted by nascent hydrogen into hydrocarbons, by ammonia into amines, by alkoxides into ethers, by alkali hydrogen sulphides into mercaptans, by potassium cyanide into nitriles, and by sodium acetate into acetic esters. (Formulate these reactions.) The alkyl halides are practically insoluble in water but are, on the other hand, miscible with organic solvents. As a consequence of the great affinity of iodine for silver, the alkyl iodides are almost instantaneously decomposed by aqueous-alcoholic silver nitrate solution, and so yield silver iodide and alcohol. The important method of Ziesel for the quantitative determination of alkyl groups combined in the form of ethers, depends on this property (cf. p. 80). 

Kumar and Agarwal (1983) modified wood with thioacetic acid in the vapour phase, which results in hydrogen sulphide being generated as the by-product. The decay and termite resistance of the wood was determined. The thioacetic acid modified wood exhibited... 

On elimination of sulphur from hydrogen sulphide an equal volume of hydrogen remains, which of course is evidence for the composition represented by the formula H S. Vapour density determinations also show that the gas consists of single H2S molecules,1 a value 34-085 2 having been obtained for the molecular weight, after making due corrections to the vapour density result. In the liquid state also there appears to be no association of the molecules and the molecular formula is still H2S. 

Quantitative Determination. — Place 0.5 gm. of the finely powdered iron sulphide in a retort, in the tubule of which is fixed a funnel-tube provided with a glass cock. After connecting the retort with a receiver containing 50 to 100 cc. of decinormal iodine solution, allow to flow into the retort, through the funnel-tube, a mixture of 20 cc. of water and 20 cc. of dilute sulphuric acid close the stop-cock, and heat to boiling. After the decomposition of the iron sulphide is complete, and the hydrogen sulphide has been entirely driven off (the iodine solution must not be fully decolorized), determine the excess of iodine by means of decinormal sodium thiosulphate. 

Bunsen 5 showed that the passage of a rapid stream of hydrogen sulphide through a hot solution of an alkali arsenate acidified with hydrochloric acid produced a precipitate of arsenic pentasulphide, and that this was a satisfactory method of determining arsenic quantitatively. These results were confirmed by McCay,6 and led to more systematic investigation of the subject,7 the result of which showed that the conditions favourable for the formation of arsenic pentasulphide, when hydrogen sulphide acts on aqueous arsenic acid or acid solutions of arsenates, are (a) a considerable excess of hydrochloric acid present, (b) a rapid passage of the gas, and (c) a comparatively low temperature—the liquid should be warm, as precipitation is extremely slow in the cold. Under these conditions arsenic pentasulphide alone is formed ... 

If arsenate and phosphate are present together, the total arsenic and phosphorus is first determined, the arsenic is then removed with hydrogen sulphide and the phosphorus determined alone.7... 

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