Bismuth sulfide, solubility

The equilibrium constant for the solubility equilibrium between an ionic solid and its dissolved ions is called the solubility product, Ksp, of the solute. For example, the solubility product for bismuth sulfide, Bi2S3, is defined as... 

There have been no fatalities in industry attributed to bismuth and it is regarded as relatively non-toxic for a heavy metal.246 The toxic problems which have been recorded have in the main been iatrogenic illnesses. A characteristic blue-black line on the gums, the bismuth line , which may persist for years, is a feature of bismuth overdosage. Soluble salts are excreted via urine and may cause mild kidney damage. Less soluble salts may be excreted in the faeces, which may be black in colour due to the presence of bismuth sulfide. Table 31 contains some toxicity data. 

Calculate the Ksp value for bismuth sulfide (Bi2S3), which has a solubility of... 

Solutions of Bi(N03)3 and Na S are both colorless. If we mix the two solutions together, a black solid precipitates. Using solubiUty rule 7 we see that all sulfides are insoluble with only a few exceptions. The bismuth ion (BT+) is not one of the exceptions. Since we know from rule 1 that NaN03 is soluble, we conclude that Na+ and NO 3 are spectator ions in this reaction and that the black precipitate is bismuth sulfide (Bi2S3), as shown in the following net ionic equation ... 

Additives and formulations that can overcome the above-mentioned problems have been reported (106). In one formulation, the electrodes may include 50-99% carbonyl iron, approximately 5-50% of potassium carbonate or a similar soluble additive that creates pores when dissolved, and approximately 5-30% of a pol5meric binder such as a poly(ethylene) binder. Alternatively, a portion of the carbonyl iron, such as approximately 5%, may be substituted with bismuth sulfide. The powder mixture may be spread on a metallic grid, such as a degreased nickel grid or a nickel coated steel... 

Bismuth hydroxide is soluble in alkaline solutions of citric and tartaric acids and of mannitol and glycerol. The structure of these complexes would be similar to that of the complexes obtained with antimony in the same conditions. These complexes, treated by alkaline sulfides, generate the black precipitate of bismuth sulfide Bi2S3. 

Metals less noble than copper, such as iron, nickel, and lead, dissolve from the anode. The lead precipitates as lead sulfate in the slimes. Other impurities such as arsenic, antimony, and bismuth remain partiy as insoluble compounds in the slimes and partiy as soluble complexes in the electrolyte. Precious metals, such as gold and silver, remain as metals in the anode slimes. The bulk of the slimes consist of particles of copper falling from the anode, and insoluble sulfides, selenides, or teUurides. These slimes are processed further for the recovery of the various constituents. Metals less noble than copper do not deposit but accumulate in solution. This requires periodic purification of the electrolyte to remove nickel sulfate, arsenic, and other impurities. 

The compound occurs in nature as mineral bismuthinite. It can be prepared in the laboratory by passing hydrogen sulfide into a solution of bismuth chloride or any soluble bismuth salt ... 

Derivation (1) By melting bismuth and sulfur together. (2) By passing hydrogen sulfide into a soluble of a bismuth salt. (3) Occurs as the mineral bismuthinite. 

Bismuth occurs mainly as bismite (a-Bi203), bismuthinite (Bi2S3) and bismutite [(Bi0)2C03] very occasionally it occurs native, in association with Pb, Ag or Co ores. The main commercial source of the element is as a byproduct from Pb/Zn and Cu plants, from which it is obtained by special processes dependent on the nature of the main product. Sulfide ores are roasted to the oxide and then reduced by iron or charcoal. Because of its low mp, very low solubility in Fe, and fairly high oxidative stability in air, Bi can be melted and cast (like Pb) in iron and steel vessels. Like Sb, the metal is too brittle to roll, draw, or extrude at room temperature, but above 225°C Bi can be worked quite well. 

The selectivity of the method is given first by the ability to stay dissolved in a solution containing tartrate, second by the color of the sulfide precipitate, and finally by the fact that the sulfide salt dissolves in sodium hydroxide. The first property distinguishes it from bismuth(III) and the other cations forming insoluble oxides in neutral or alkaline solutions. But since the test does not show that a precipitate is formed in pure water, which dissolves when tartrate is added, all water-soluble cations are not excluded. So it should be viewed as a trick to facilitate dissolution only and not a part of the identification. The color of the sulfide precipitate is unique, and it is the most important criterion for a positive identification if there is any doubt when judging the result, preparing a positive control would be constructive. The solubility of the sulfide salt in sodium hydroxide is a characteristic shared with, for example, the sulfide salt of arsenate, and in classic inorganic separation the sulfide precipitate solubility in hydrochloric acid or polysulfide is used instead. " ... 

Along with the sulfide and sulphate, precipitation of lead chromate Is one of the most popular separations In lead radlochemlstry. This precipitation serves as a satisfactory separation from Copper, zlnci and other elements that form soluble chromates In acetic acid solution. Thallium, antimony, bismuth and barium are precipitated or carried with the lead chromate however, bismuth contamination can be reduced by leaching the... 

Moore (M5) reports that excellent separation of traces of lead from small amounts of bismuth can be achieved by adding 0.02 grams of copper to 25 ml of the lead and bismuth in 2N hydrochloric acid and saturating the solution with hydrogen sulfide, gas. The copper sulfide precipitate was then filtered and washed with 2N hydrochloric acid saturated with hydrogen, sulfide. The lead was recovered from the filtrate and bismuth from the precipitate. The lead presumably was kept from precipitation because of formation of soluble lead chloride complexes. 

Consequently, addition of soluble mercury or lead salts or a little hydrous bismuth oxide yields the respective black sulfide. 

While some cathodic poisons such as sulfides and selenides are adsorbed on the metal surface, compounds of arsenic, bismuth, and antimony are reduced at the cathode to deposit a layer of the respective metals. Sulfides and selenides generally are not useful inhibitors because they are not very soluble in acidic solutions, they precipitate many metal ions, and they are toxic. Arsenates are used to inhibit corrosion in strong acids, but in recent years the trend has been to rely more on organic inhibitors because of the toxicity of arsenic. 

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