Soluble salts of lead

In basic solutions basic nitrates are formed which precipitate however. In the presence of excess acetate, basic lead acetate Pb(0H)C2H202 Is formed which Is soluble In basic solution and can be used to prevent precipitation or hydrolysis of lead In neutral or weakly basic solutions. 

The only oxidation state of importance In aqueous solution Is the +2 state. Compounds of the +4 plumbic Ion are well known but are Invariably unstable or Insoluble in aqueous solution. Due to the dominant stability of the +2 state In aqueous solution oxidation -reduction reactions are of minor Importance In lead separations and determinations. The notable exceptions are anodic oj ldatlon to the dioxide and reduction to the metal either cathodloally or by Internal electrodeposltlon. 111000 reactions have been used for the separation and determination of lead and are dlsoussed In detail In section IV-10 of this report. 

The Information available (h4), (15) and (S4) on the solubility of the common soluble lead compounds is shown In Table lil. 

The common Insoluble salts of lead are summarized In Table IV. Some of these salts as well as some of the other lead salts and organic complex precipitates are discussed below. 

Lead carbonate Is slightly soluble In water. Is Insoluble In basic solution and Is soluble In ammonium acetate and In acid solution. The carbonate Is frequently formed during separations by metatheslzlhg a lead sulphate precipitate to lead carbonate through heating and stirring the lead sulfate wltii portions of sodium carbonate solution. 

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With sparingly soluble salts of lead, the compactness of the deposits may be strongly influenced by the concentration of the relevant anion. Very low concentrations frequently resulting in imperfect coatings. 

Lead sulfate precipitates when an aqueous solution of lead nitrate or other soluble salt of lead is treated with sulfuric acid. 

Chromate of Lead—TbO, Or Of—chrome yellow.— When chromate of potassa is added to a soluble salt of lead, both solutions being hot, a fine colored anhydrous precipitate is obtained if the solutions are cold, tho precipitate wilt bo pale yellow, and will contain an equivalent of water. 

The solubility of lead chromate in water is exceedingly small indeed, the chromate is probably the least soluble salt of lead. It is practically insoluble also in dilute acetic acid consequently chromate ions in presence of acetic acid constitute a very delicate test for lead ions in solution. The solubility of lead chromate in water at 25° C. is about 10 grams per litre according to Kohlrausch, but von Hevesy and Paneth obtained the value 1-2 X 10 grams per litre by employing... 

It has long been known that the rate of silane homopolymerization is increased by pH or metal salt catalysis and decreased by increased concentration and higher temperature. Most silanes are hydrolyzed most rapidly at pH between 3 and 5. Solution stability depends on the rate of homopolymerization to siloxane polymer. This is affected by pH, the presence of soluble salts of lead, zinc, iron, etc., and silane concentration. A pH in the range of 4 to 5 generally favors the monomeric form and retards polymerization. The formation of homopolymer can be detected as silane loses solubility and forms a gel which is not active in the coupling process. It is, then, desirable to retain silane in the monomeric or dimeric form. In the next two steps a bond is formed with the substrate (e.g., filler). 

Chromate of lead, PbO, CrOs, is an insoluble powder, of a very fine yellow colour, much used in painting, under the name of chrome yellow. It is formed by the action of soluble salts of lead on chromate, or bichromate of potash. 

Self-Test 11.11B The solubility product of lead(Il) fluoride, PbF, is 3.7 X 10 s. Estimate the molar solubility of the salt. 

The feasibility of the above reaction ensues from the data on the solubility products of lead sulfate and lead carbonate salts. Evidence abounds that both sulfate and carbonate ions are present. 

Gruse and Stevens (24) list still other metallic constituents which may be present in recognizable amounts in the ash from various petroleums, including tellurium, barium, lead, manganese, chromium, and silver. According to these authors, oil-soluble salts of petroleum acids probably account for the small portions of most metallic constituents present in crude oil. 

Lead nitrate is one of the most readily prepared salts of lead, since it is of moderate solubility and can be obtained in well-formed anhydrous crystals, Pb(NOs)2. In it lead appears in its usual state of oxidation, which corresponds to that of the oxide PbO indeed, the salt is actually prepared by treating this oxide (litharge) with nitric acid. 

By addition of concentrated aqueous solutions of soluble salts of silver, lead, thallium, and mercury, the following insoluble salts have been obtained Ag2PtI4(OH)2 PbPtI4(OH)2.Pb(OH). Tl2PtI4(OII)2 and HgPtI4(OH)2. 

This can be achieved by making a soluble salt of the drug which is rapidly absorbed from the site of administration. In the case of s.c. or i.m. injections the same objective may be obtained with hyaluronidase, an eri2yme which deploymerises hyaluronic acid, a constituent of connective tissue that prevents the spread of foreign substences, e.g. bacteria, drugs. Hyaluronidase combined with an i.m. injection e.g. a local anaesthetic, or a subcutaneous infusion, leads to increased permeation with more rapid absorption. Hyaluronidase can also be used to promote resorp>-tion of tissue accumulation of blood and fluid. 

The thiophenols are liquids of unpleasant odours the higher members of the series are solids. Like the mercaptans of the aliphatic series, they form difficultly soluble salts with lead and mercury. 

According to the temperature at which the sulphonation takes place, more of one than of the other acid is formed at lower temperatures an excess of the a-add is obtained, at higher an excess of the /3-add. If the mixture is heated to too0, a mixture of 4 parts of the a-acid and 1 part of the /3-add is formed, while at 170° a mixture of the 3 parts of the /3-add and 1 part of the a-add is obtained. In order to separate the sulphonic adds from the excess of sulphuric acid, advantage is taken of the fact that sulphonic adds differ from sulphuric add in that they form soluble salts of caldum, barium, and lead, as mentioned under benzenesulphonic acid. For the separation of the sulphonic acid from sulphuric add, the caldum salt is prepared by neutralising the acid mixture with chalk or lime, since it is cheaper than lead carbonate or barium carbonate. This method is followed technically on the large. scale as well as in laboratory preparations. Since the caldum salts of the two isomeric sulphonic adds possess a very different solubility in water,—at io° 1 part of the a-salt dissolves in 16.5 parts of water, and 1 part of the /3-salt dissolves in 76 parts of water,—the /3-salt, which is more difficultly soluble, and consequently crystallises out first, can be separated by fractional crystallisation from the a-salt which remains in solution. For the conversion into naphthol the caldum salt cannot be used directly it must first be changed into the sodium salt by treatment with sodium carbonate ... 

This auto-catalytic process is characterized by a rather long induction period, which can be shortened by initiating the conversion by the introduction of small amounts (0.05 to 0.5 per cent weight in relation to the feed) of cumyl hydroperoxide or of its sodium salt Other initiators or oxidation catalysts are sometimes introduced these may be soluble salts of heavy metals (Mn, Co, Cu) or alkaline and alkaline earth derivatives of lead, bismuth, tin and antimony. "... 

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