Difference between revisions of "Lead"
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Revision as of 19:40, 2 August 2015
Lead is a chemical element with symbol Pb and atomic number 82. It is a very heavy and dense metal, and is well-known for its toxicity.
Contents
Properties
Chemical
Lead is resistant to certain acids such as sulfuric acid but will react with nitric acid to form lead nitrate, one of very few water-soluble lead compounds. Hot hydrochloric acid can also be used to convert lead into the poorly soluble lead(II) chloride.
Freshly cut lead will oxidize in air. Lead compounds span a wide range of colors, and the pigments white lead, red lead, and chrome yellow are all derived from it. Solutions can be tested for lead by adding a few drops of potassium iodide solution, which forms a bright yellow precipitate of lead(II) iodide. Sodium sulfide can also be used, precipitating black lead sulfide.
Physical
Lead is a soft and malleable heavy and post-transition metal. Metallic lead has a bluish-silver color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has one of the lowest thermal and electrical conductivity of all metals. Lead is usually quickly identified from its high density and rather low melting point at 327 degrees Celsius.
Availability
Lead is available for sale as bars or ingots, in various purities. Certain wheels weights are made of lead or lead alloy (those of purer lead are very soft). Car batteries contain lead and lead oxide. Many items made in the earlier 20th century are a good source of lead, either pure or as alloy: old water pipes are a good bulk source; some car battery cable contacts were made of lead; very old hard drives tend to have counterweights made of lead; solders contain lead-tin alloy; scuba diving weight belts. The standard firearm bullets and shotgun pellets are also made of lead. Finally, lead fishing weights are widely available in outdoor or department stores.
Preparation
Lead can be prepared by reducing one of its oxides with lead sulfide or from ions via electrowinning.
Projects
- Lead acetate
- Lead dioxide synthesis
- Lead tetroxide synthesis
- Lead electrodes
- Lead battery
Handling
Safety
While lead is resistant to chemical attacks, it will rapidly oxidize into compounds that are extremely toxic to living beings. Lead poisoning is one of the most studied form of heavy metal poisoning in medicine and the nasty effects are well understood. Proper protection such as gloves should be worn when handling the metal, especially if its surface is oxidized. Because of its low melting point, lead is sometimes a popular use in home casting. However because it gives off toxic fumes, protection masks should be worn and if possible use another low-temperature melting metal.
Most lead compounds are poorly soluble in water, but lead(II) acetate and lead(II) nitrate are quite soluble and therefore are very toxic.
Storage
Since it does not form volatile compounds under standard conditions, it's not necessary to be stored in special containers. If you want to prevent it from oxidizing, lead may be stored in a closed bottle under inert atmosphere, carbon dioxide is best. It's recommended to avoid storing it underwater or in any other liquids, as it will slowly oxidize, since there is some oxygen dissolved in liquid, and some lead oxide may come off and contaminate the liquid.
Disposal
Lead scraps can be taken to metal recycling facilities. Lead compounds should be converted to insoluble forms, before being taken to a hazardous waste facility.
