Hydrogen sulphide reagents

Hydrogen sulphide is used in the preparation of metal sulphides, oil additives ete., in the purifieation and separation of metals, as an analytieal reagent and as raw material in organie synthesis. It burns in air with a blue flame ... 

A rapid and clean oxidation of sulphides to sulphoxides can also be carried out using the titanium(III) trichloride/hydrogen peroxide reagent. On a milimole scale, the oxidation takes place in a time shorter than 20 min upon addition of a solution of hydrogen peroxide to a solution of the sulphide and titanium(III) trichloride in methanol at room temperature. It was suggested that the formation of a sulphoxide in this reaction resulted from a direct coupling of the hydroxy radical with cation radical 20 formed at the sulphur atom of the sulphide (equation 6). 

Ammonium hydrogen sulphide is also a very suitable reagent for the reduction of nitrocompounds to arylhydroxylamines it is used in alcoholic solution in the cold.1... 

Formation and Preparation.—1. From its Elements.—(a) Above 200° C. hydrogen and sulphur interact with appreciable velocity, forming hydrogen sulphide.3 Relow 350° C. the combination proceeds slowly until one or other of the reagents is entirely consumed, but above this temperature, although the reaction is naturally more rapid, the final product is an equilibrium mixture, the change being representable thus ... 

With ammonia, the gas combines to form ammonium sulphide or ammonium hydrosulphide, according to the relative quantities of the reagents.4 The alkaloids, which may be regarded as organic derivatives of ammonia, also combine with hydrogen sulphide, forming crystalline salts such salts of cinchonine, quinine, strychnine, brucine and nicotine have been known for many years.5 When heated in the gas, the alkali metals yield the acid sulphides ... 

Whenever sulphur dioxide, water and nascent sulphur meet, for example in the action of water on sulphur chloride, of mineral acids on a thiosulphate, or of hydrogen sulphide on aqueous sulphur dioxide solution, formation of polythionic acids is likely to occur. Dalton 1 in 1812 demonstrated that the last-named reagents gave rise to an acid liquid, a result which was confirmed later by Thomson 2 in 1846 Wackenroder 3 proved the presence of pentathionic acid in the liquid, since which date the aqueous reaction product has been known as Wackenroder s Solution. ... 

Selenic Acid, HaSe04.—This acid was first prepared by Mitscher-lich in 1827, who suspended lead selenate in water and precipitated the lead by means of hydrogen sulphide. By the oxidation of aqueous solutions of selenious acid with suitable reagents, e.g. chlorine or bromine, selenic acid may also be obtained.6 When chlorine is used, any hydrogen chloride must be removed as soon as it is formed, for selenic acid is reduced by hot hydrogen chloride to selenious acid, with liberation of chlorine the process is best carried out6 by passing a... 

To detect an arsenite and an arsenate in the presence of each other, the neutral solution should be treated with ammonia and magnesia mixture. The precipitate, treated with Bettendorff s reagent, gives a black precipitate of arsenic, indicating arsenate the filtrate, acidified with hydrochloric acid and treated with hydrogen sulphide, yields a precipitate of arsenious sulphide, indicating arsenite.6... 

The sensitivity of hydrogen sulphide as a reagent for detecting ter-valent arsenic by the yellow colour produced in the presence of hydrochloric acid has been stated in widely different terms 4 the smallest amount thus detected is given as 1 part of As203in 1,024,000 parts of water.5... 

When dilute reagents are used—for example, nickel sulphate and ammonium sulphide in dilute aqueous solution—probably the a compound is first formed, and then, when the solubility of this substance is exceeded, a precipitate separates out which subsequently more or less completely polymerises to the [3 and y forms. This suffices to explain the well-known fact in qualitative analysis that whilst nickel sulphide cannot be precipitated in acid solution by hydrogen sulphide, yet when once precipitated in alkaline solution it is very difficult to dissolve again completely in dilute mineral acid.11... 

Precipitation of sulphides Hydrogen sulphide gas is a frequently used reagent in qualitative inorganic analysis. When hydrogen sulphide gas is passed into a solution, metal sulphides are precipitated. For this precipitation the rule mentioned above can be applied precipitation may take place only if the product of concentrations of metal ions and sulphide ions (taken at proper powers) exceed the value of the solubility product. While the concentration of metal ions usually does fall into the range of 1-10 3 mol 1, the concentration of sulphide ion may vary considerably, and can easily be selected by the adjustment of the pH of the solution to a suitable value. 

Alternatively, a saturated aqueous solution of hydrogen sulphide can be used as a reagent. This can most easily be prepared in the bottle B of the apparatus shown in Fig. II. 6. Such a reagent can most conveniently be used in teaching laboratories or classroom demonstrations when studying the reactions of ions. For a quantitative precipitation of sulphides (e.g. for separation of metals) the use of hydrogen sulphide gas is however recommended. 

The group reagents used for the classification of most common cations are hydrochloric acid, hydrogen sulphide, ammonium sulphide, and ammonium carbonate. Classification is based on whether a cation reacts with these reagents by the formation of precipitates or not. It can therefore be said that classification of the most common cations is based on the differences of solubilities of their chlorides, sulphides, and carbonates. 

The great insolubility of lead sulphide in water (4-9 x 10 11 g -1) explains why hydrogen sulphide is such a sensitive reagent for the detection of lead, and why it can be detected in the filtrate from the separation of the sparingly soluble lead chloride in dilute hydrochloric acid. 

Group reagent hydrogen sulphide (gas or saturated aqueous solution). 

Group reagent hydrogen sulphide (gas or saturated aqueous solution) in the presence of ammonia and ammonium chloride, or ammonium sulphide solution. 

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