Difference between revisions of "Mercury"
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Mercury (also known as quicksilver) is a chemical element with the symbol Hg (from its latin name hydrargyrum, meaning silver water) and atomic number 80. It is the only liquid metal at room temperature.
Contents
Properties
Chemical
Mercury is resistant to most acids, although oxidizing acids, such as concentrated sulfuric acid, nitric acid or aqua regia dissolve it to give its respective sulfate, nitrate, and chloride salts. Mercury has two potential oxidation states (I) and (II). Mercury(I) nitrate, or mercurous nitrate, can be prepared by dissolving mercury in cold dilute nitric acid, while mercury(II) nitrate, mercuric nitrate, can be prepared by dissolving the metal in hot concentrated nitric acid. Like silver, mercury reacts with atmospheric hydrogen sulfide, but unlike silver will also react with solid sulfur, forming mercury sulfide (cinnabar). Elemental sulfur is used to absorb mercury spills and vapors. Mercury will also form amalgams with gold, aluminium or alkali metals.
Physical
Mercury is a dense, silvery-white liquid metal. It is a poor conductor of heat, but a fair conductor of electricity. Mercury melts at −38.83 °C and boils at 356.73 °C. Unlike most metals that melt at low temperatures, liquid mercury in does not wet glass.
Availability
Mercury can be found in medical mercury thermometers. The packaging of these thermometers comes with a warning, that the product contains mercury and is dangerous for the environment. Old blood pressure meters also contain mercury. Other old devices that contain mercury are: old tilt switches, mercury electrodes, mercury manometers, mercury batteries, etc. Old amalgam fillings contain mercury. Some light sources, such as fluorescent lamps contain a minute amount of mercury, albeit too small to be of any importance.
In EU the sale of mercury is restricted.
Norway enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, in 2008.
Preparation
Mercury can be prepared by reducing its salt with a reducing metal (though it's best avoiding metals that form amalgam).
A more dangerous method involves roasting cinnabar in a current of air and condensing the resulting mercury vapor. This method is extremely dangerous, as it generate highly toxic mercury vapors.
Projects
The use of mercury and mercury compounds in experiments carries a high risk of poisoning, mainly due to its vapors and the volatility of some of its compounds. The biggest risk however, is due to the low LD50 of most of its compounds, their ability to be absorbed through the skin and long delay between poisoning and first symptoms. Any experiments must be performed either outside, in a fume hood or, if possible in a glovebox.
- Pharaoh's snake (thermal decomposition of mercury(II) thiocyanate)
- Castner–Kellner process
- Make amalgams
- Mercury(II) nitrate synthesis
- Mercury(II) chloride synthesis
- Mercury fulminate synthesis
Handling
Safety
Elemental mercury in its liquid form is not very reactive, but its vapors and compounds are extremely toxic. Mercury ions have a long half life in the body, and are potent cumulative toxins. If the metal is dropped onto a porous surface, such as wood, the metal can split into micron-sized beads which will evaporate and fill the room with extremely toxic mercury vapor. Many compounds can rapidly absorb through the skin and cause severe mercury poisoning. This leads to severe medical problems and can eventually lead to death, usually after a longer period of time.
Storage
Mercury should be stored in closed glass or thick plastic bottles, in a special hazardous substance cabinet, with a proper label. A bed of elemental sulfur can also be used, to absorb the leaking mercury vapors.
Mercury compounds should be stored in a similar way.
Disposal
Mercury spillings can be removed by adding a mixture of powdered elemental sulfur and zinc. The resulting solid must be taken to special disposal centers.
