- Structure
- Electronic configuration
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Solubility
- Other properties
- Applications
- In catalysis of chemical reactions
- In the treatment of water contaminated with chromium (VI)
- In the preparation of photothermographic copies
- In mixtures for temporary sealing
- In various applications
- Recent studies
- Risks
- References
The lead hydroxide is a white inorganic solid in which the lead (Pb) is in the 2+ oxidation state. Its chemical formula is Pb (OH) 2. According to some sources of information, it can be prepared by adding an alkali to a solution of lead nitrate (Pb (NO 3) 2). It can also be obtained by electrolysis of an alkaline solution with a lead anode.
However, there is a contradiction by the various authors, since it has long been stated that there is only one stable solid form of lead (II) hydroxide, formulated as 3PbO.H 2 O, or lead (II) oxide hydrate.
Lead hydroxide Pb (OH) 2 in a test tube. Author: Ondřej Mangl. Source: Vlastní sbírka. Source: Wikipedia Commons.
Lead hydroxide is very poorly soluble in water. Its uses include its usefulness to remove chromium (VI) ions from wastewater, as a catalyst in chemical reactions, or to increase the efficiency of other catalysts.
It has also been used as a pH stabilizer in mixtures for sealing permeable formations, as an ingredient in heat-sensitive paper, and as an electrolyte in sealed nickel-cadmium batteries.
Another of its uses is in protective screens against radiation in buildings and to stabilize plastic resins against degradation.
Exposure to Pb (OH) 2 should be avoided as all lead compounds are toxic to a greater or lesser degree.
Structure
Pb (OH) 2 is a white amorphous solid. It does not have a crystalline structure.
Electronic configuration
The electronic structure of lead metal is:
4 f 14 5 d 10 6 s 2 6 p 2
Where is the electron configuration of the noble gas xenon.
Its most stable chemical form in solution is that of the Pb 2+ ion, which is a present in Pb (OH) 2, in which the two electrons of the 6 p layer are lost, resulting in the following electronic configuration:
4 f 14 5 d 10 6 s 2
Nomenclature
- Lead (II) hydroxide.
- Plumb hydroxide.
- Lead (II) dihydroxide.
- Lead (II) oxide hydrate.
Properties
Physical state
Amorphous white solid.
Molecular weight
241.23 g / mol.
Melting point
It dehydrates when it reaches 130ºC and decomposes when it reaches 145ºC.
Solubility
Weakly soluble in water, 0.0155 g / 100 mL at 20 ºC. Slightly more soluble in hot water.
It is soluble in acids and alkalis. Insoluble in acetone.
Other properties
The lead (II) ion, or Pb 2+, is partially hydrolyzed in water. It has been experimentally verified by spectrometry of the UV-Visible region, that the Pb 2+ species present in alkaline solutions of lead (II) perchlorate (Pb (ClO 4) 2) are the following: Pb (OH) +, Pb (OH) 2, Pb (OH) 3 - and Pb (OH) 4 2+.
Applications
In catalysis of chemical reactions
Pb (OH) 2 is useful in the synthesis of carboxylic acid amides as it is used to incorporate a certain percentage of lead to the palladium (Pd) metallic catalyst. In this way the catalytic efficiency of palladium is increased.
It has also been used as a catalyst for the oxidation of cyclododecanol.
In the treatment of water contaminated with chromium (VI)
The hexavalent chromium ion Cr 6+ is a polluting element because even in minimal concentrations it is toxic to fish and other aquatic species. Therefore, in order for water contaminated with Cr 6+ to be discharged into the environment, it must be treated until the complete removal of the chromium it contains.
Lead hydroxide has been used to remove Cr 6+, even in very small amounts, as it forms an insoluble lead chromate compound (PbCrO 4).
Lead chromate, insoluble in water. Author: FK1954. Source: Own work. Source: Wikipedia Commons.
In the preparation of photothermographic copies
Photothermographic copying has been used to make copies of documents.
It involves placing the original document in heat-conductive contact with a blank sheet of paper and subjecting both to intense infrared radiation (heat).
This is done in such a way that the printed part of the original absorbs a portion of the radiant energy. This heat causes the image of the original to develop on the blank sheet.
In this process, the blank sheet of paper must be formulated such that when heated it can change to a contrasting color. That is, the paper must be sensitive to heat.
The heat-generated image can be formed by both a physical change in the blank sheet and a heat-induced chemical reaction.
Lead hydroxide has been used in the preparation of special paper for photothermographic copies. It is applied to paper in the form of a dispersion with a volatile organic solvent so that a coating is formed.
The lead hydroxide coating must be on the inside, this means that another coating is placed on top, in this case a thiourea derivative.
During the heating of the paper, a chemical reaction occurs in which dark-colored lead sulphides are formed.
Paper made in this way produces well defined prints where the graphic part is black in contrast to the whiteness of the paper.
In mixtures for temporary sealing
Sometimes it is necessary to temporarily seal permeable formations in which openings have been made. For this, mixtures are used capable of forming a mass that supports appreciable pressures and then liquefies so that the plug stops working and allows the flow of fluids through the formation.
Some of these mixtures contain gums derived from sugars, hydrophobic compounds, an organic polymer that keeps the ingredients in suspension, and a pH control agent.
Lead hydroxide has been used as a pH controlling compound in this type of mixture. Pb (OH) 2 releases hydroxyl ions (OH -) and helps maintain the pH between 8 and 12. This ensures that the hydrophobically treated rubber does not swell due to acidic conditions.
In various applications
Pb (OH) 2 serves as the electrolyte in sealed nickel-cadmium batteries. It has been used in electrical insulating paper, in the manufacture of porous glass, in the recovery of uranium from sea water, in lubricating greases and in the manufacture of radiation shields in buildings.
Author: Michael Gaida. Source: Pixabay
As a raw material to produce other lead compounds, particularly in the plastics industry, to produce stabilizers for polyvinyl chloride resins to resist thermal degradation and that caused by UV light.
Recent studies
The use of a derivative of Pb (OH) 2, lead (II) hydroxychloride, Pb (OH) Cl, has been investigated as a novel anode in lithium (Li) batteries or energy storage systems. The initial recharge capacity of Pb (OH) Cl was found to be high.
Lithium ion batteries. Author: Dean Simone. Source: Pixabay
However, in the electrochemical process the formation of Pb (OH) 2 and PbCl 2 occurs at the expense of Pb (OH) Cl and the formation of holes on the surface of the electrode is observed. As a result, the cyclical charge and recharge property decreases due to damage to the PB (OH) Cl electrode during the repetition of these cycles.
Therefore, the use of these Pb (OH) Cl electrodes in lithium batteries must be reviewed to find a solution to this problem.
Risks
Lead is toxic in all its forms but to varying degrees depending on the nature and solubility of the compound. Pb (OH) 2 is very poorly soluble in water, so it is likely to be less toxic than other lead compounds.
However, the toxic effect of lead is cumulative, therefore prolonged exposure to any of its forms should be avoided.
The most common symptoms of plumbismus (lead poisoning) are gastrointestinal: nausea, diarrhea, anorexia, constipation, and colic. Lead absorption can affect hemoglobin synthesis and neuromuscular function.
In women, lead can decrease fertility and harm fetuses. In cases of high levels of Pb in the blood, encephalopathies occur.
To avoid this, in industries where there is a possibility of exposure, respiratory protection, protective clothing, continuous exposure monitoring, isolated canteens and medical supervision should be used.
References
- Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 15. Fourth Edition. John Wiley & Sons.
- Nimal Perera, W. et al. (2001). An Investigation of the Lead (II) -Hydroxide Inorg. Chem. 2001, 40, 3974-3978. Recovered from pubs.acs.org.
- Jie Shu, et al. (2013). Hydrothermal fabrication of lead hydroxide chloride as a novel anode material for lithium-ion batteries. Electrochimica Acta 102 (2013) 381-387. Recovered from sciencedirect.com.
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- Otto, Edward C. (1966). US Patent No. 3,260,613. Heat-sensitive sheet for thermographic copying. July 12, 1966.
- Nimerick, Kenneth H. (1973). Method for temporarily sealing a permeable formation. US Patent No. 3,766,984. October 23, 1973.
- Nieuwenhuls, Garmt J. (1974). Process for treating water contaminated with hexavalent chromium. US Patent No. 3,791,520. February 12, 1974.
- Nishikido Joji, et al. (nineteen eighty one). Process of preparing carboxylic acid amides. US Patent No. 4,304,937. December 8, 1981.
- Ullmann's Encyclopedia of Industrial Chemistry. (1990). Fifth Edition. Volume A 15. VCH Verlagsgesellschaft mbH.