Difference between revisions of "Lead(II) acetate"

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Lead(II) acetate

Large lead(II) acetate trihydrate crystals
Names
IUPAC name Lead(II) ethanoate
Preferred IUPAC name Lead(II) ethanoate
Systematic IUPAC name Lead(II) ethanoate
Other names Lead diacetate Plumbous acetate Salt of Saturn Sugar of lead
Properties
Chemical formula	C4H6O4Pb Pb(CH3COO)2
Molar mass	325.29 g/mol (anhydrous) 379.33g/mol (trihydrate)
Appearance	White powder or colorless, efflorescent crystals
Odor	Slightly acetic
Density	3.25 g/cm3 (20 °C, anhydrous) 2.55 g/cm3 (trihydrate) 1.69 g/cm3 (decahydrate)
Melting point	anhydrous 280 °C (536 °F; 553 K) 75 °C (167 °F; 348 K) trihydrate 200 °C (decomposes) decahydrate 22 °C (72 °F; 295 K)
Boiling point	Decomposes
Solubility in water	19.80 g/100 ml (0 °C) 44.31 g/100 ml (20 °C) 69.50 g/100 ml (30 °C) 218.3 g/100 ml (50 °C)
Solubility	Soluble in alcohols, glycerol
Solubility in glycerol	Anhydrous 20 g/100 g (15 °C) Trihydrate 143 g/100 g (20 °C)
Solubility in methanol	Anhydrous 102.75 g/100 g (66.1 °C) Trihydrate 74.75 g/100 g (15 °C) 214.95 g/100 g (66.1 °C)
Thermochemistry
Std enthalpy of formation (ΔfHo298)	−960.9 kJ/mol (anhydrous) −1848.6 kJ/mol (trihydrate)
Hazards
Safety data sheet	Sigma-Aldrich (trihydrate)
Related compounds
Related compounds	Lead(IV) acetate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Lead(II) acetate is a toxic compound with a chemical formula of Pb(CH₃COO)₂ (sometimes shortened to PbAc₂) that is often encountered during home chemistry with lead, due to its high solubility compared to most other lead compounds. It is also easy to prepare with common household chemicals.

Properties

Chemical

Lead(II) acetate will precipitate lead(II) chloride and lead(II) sulfate on addition of the corresponding strong mineral acids, but lead(II) nitrate will not precipitate in this way, due to relative high solubility.

Pb(CH₃COO)₂ + 2 HCl → PbCl₂ + 2 CH₃COOH

Pb(CH₃COO)₂ + H₂SO₄ → PbSO₄ + 2 CH₃COOH

Lead(II) acetate reacts with hydrogen sulfide to from a grey precipitate of lead(II) sulfide. Because of the stark color change, this reaction can be used as a test for the presence of hydrogen sulfide.

Pb(CH₃COO)₂ + H₂S → PbS + 2 CH₃COOH

Physical

Lead acetate forms clear transparent crystals that dissolve to form a colorless solution. It is soluble in water, methanol, ethanol, glycerol. It is odorless, but has a characteristic sweet taste.

Lead acetate is highly poisonous, in this way it is rather similar to barium acetate.

Availability

Due to their toxicity, lead salts have been replaced by less toxic compounds in most applications. Therefore, lead acetate is really only available bought as a chemistry reagent. Toxicity does not generally affect a shipping cost the same way that reactive or dangerous chemicals such as sodium metal have a high shipping cost, therefore online purchasing of lead acetate can be economical. Sometimes lead acetate can be found in hydrogen sulfide testing paper strips.

Preparation

Lead(II) acetate can be formed by adding lead in a solution of acetic acid and hydrogen peroxide. It can also form from the action of acetic acid on several lead compounds, such as lead hydroxide, oxide or carbonate.

If the metallic lead used in reaction is impure and has other elements such as antimony in its composition, antimony oxide will precipitate as a very fine suspension, which is too fine to be filtered using normal filter paper, even if you use multiple layers. The fine oxide can be removed by filtering the impure PbAc₂ aqueous solution through a layer of celite. While other metals, such as zinc, tin or cadmium than may be present in the lead will also form their respective acetates, the amount of these acetates is quite low, and can be removed via recrystallization from acetic acid or water.

Projects

Many lead compounds such as lead(II) chloride and lead(II) sulfate are poorly soluble in water. However lead(II) acetate is soluble, so it creates lead(II) ions in solution. This is useful for double displacement reactions that precipitate a desired insoluble lead salt like lead(II) picrate, from a solution of lead acetate and picric acid.

Other:

• Glacial acetic acid
• Lead(IV) acetate synthesis
• THF synthesis
• Detection of hydrogen sulfide
• Make Tree of Saturn

Handling

Safety

Lead salts are highly toxic. Many home chemists will refuse to work with lead, as accidental exposure is far too easy to do, and lead will stay in your body each time this happens, accumulating and poisoning you. Lead(II) acetate is more dangerous as it is a soluble form of the lead(II) ion, making it more easily accessed by the internal workings of your body.

Lead(II) acetate also has the misfortune of being quite sweet and potentially mistaken for sugar, even though gram quantities could kill a fully grown man. Therefore proper labeling and storage of this compound is of high importance, as the danger of the salt appears low on observation of the solid or solution not only to you but to small creatures such as pets as well.

Storage

Lead(II) acetate should be stored in closed bottles, in a cool, dry, well ventilated place.

Disposal

Dealing with lead carries the burden of responsible disposal of any waste compounds, especially soluble ones. Lead is a serious environmental toxin, and will stay in the ground for years or make its way to the food chain if simply dumped. The least one can do is reduce the toxic salts back to the metal, which is not such an environmental pollutant (the metal still needs to be responsibly disposed of as well however).

References

Relevant Sciencemadness threads

• The lead salts preparation thread!