Arsenic

Arsenic . Chemical element, whose symbol is As and its atomic number, 33. Arsenic is widely distributed in nature (about 5 x 10-4% of the earth’s crust). It is one of the 22 known elements that are composed of a single stable nuclide, 7533As; the atomic weight is 74,922. 17 other radioactive nuclides of As are known.

Summary

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  • 1 Natural state
  • 2 Applications
  • 3 Health Effects of Arsenic
  • 4 Compounds
  • 5 External links
  • 6 Sources

Natural state

There are three allotropes or polymorphic modifications of arsenic:

  • The yellow cubic shape is obtained by condensation of vapor at very low temperatures.
  • Black polymorphic b, which is isostructural with black phosphorus.

Both revert to the more stable form, the l, gray or metallic, of rhombohedral arsenic, on heating or on exposure to light.

  • The metallic form is a moderate electrical and thermal conductor, brittle, easy to break and of low ductility.

Arsenic is found naturally as a cobalt mineral, although it is usually found on the surface of rocks combined with Sulfur or metals such as Manganese , Iron , Cobalt , Nickel , Silver or Tin . The main mineral of arsenic is FeAsS (arsenopyrite, pilo); other metallic arsenides are the minerals FeAs 2 ( löllingite ), NiAs (nicolite), CoAs 2 (bright cobalt), NiAs 2 (gersdorfite) and CoAs 2 (esmaltite). Natural arsenates and thioarseniates are common and most sulfide minerals contain arsenic such asAlacranita . As 4 S 4 (realgarita) and As 4 S 6 (orpiment) are the most important minerals that contain sulfur. The oxide, arsenolite, As 4 O 6 , is found as a product of the alteration due to atmospheric agents of other arsenic minerals, and it is also recovered from the dust collected from the pipes during the extraction of Ni, Cu and Sn; It is also obtained by calcining Fe, Co or Ni arsenides with air or Oxygen . The element can be obtained by calcination of FeAsS or FeAs 2 in the absence of air or by reduction of As 4 O 6with carbonate, when As 4 is sublimated .

Applications

Elemental arsenic has few uses. It is one of the few minerals available with 99.9999+% purity. In the solid state it has been widely used in laser materials GaAs and as an accelerating agent in the manufacture of various devices. Arsenic oxide is used in the manufacture of glass . Arsenic sulfides are used as Pigments and in fireworks. Hydrogen arsenate is used in medicine, as well as other arsenic compounds. Most of the medicinal application of arsenic compounds is based on their toxic nature

Health effects of Arsenic

Arsenic is one of the most toxic elements that can be found. Due to its toxic effects, inorganic arsenic bonds occur naturally in the soil in small amounts. Humans can be exposed to Arsenic through food, water, and air.

Exposure can also occur through skin contact with soil or water containing Arsenic.

Arsenic levels in food are quite low, it is not added due to its toxicity, but Arsenic levels in fish and shellfish can be high, because fish absorb Arsenic from the water where they live. Luckily this is mostly the least harmful form of organic arsenic, but fish that contain significant amounts of inorganic arsenic can be a danger to human health.

Exposure to Arsenic may be higher for people who work with Arsenic, for people who drink significant amounts of wine, for people who live in houses that contain wood preservatives, and for people who live on farms where Arsenic from pesticides has been applied in the past.

Exposure to inorganic arsenic can cause several health effects, such as irritation of the stomach and intestines, decreased production of red and white blood cells, skin changes, and irritation of the lungs. It is suggested that taking significant amounts of inorganic arsenic can enhance the chances of developing cancer, especially the chances of developing cancer of the skin, lung, liver, and lymph.

Very high exposures to inorganic arsenic can cause infertility and abortion in women, can cause skin disturbance, loss of resistance to infection, heart disturbance, and brain damage in both men and women. Finally, inorganic arsenic can damage DNA . Organic Arsenic cannot cause cancer, nor can it damage DNA. But exposures to high doses can cause certain effects on human health, such as nerve damage and stomach pain.

Compounds

The table shows the physicochemical properties of the most common arsenic compounds:
Compound Formula Melting point (° C) Boiling point (° C) Density (g / cm 3 ) Solubility in water (g / L)
Arsenic Ace 613   5.73 at 14 o C Insoluble
Arsenic trioxide Ace 2 O 3 312.3 465 3.74 37 to 20 o C
Arsenic pentoxide Ace 2 O 5 315   4.32 1500 to 16 o C
Arsenic sulfide As 2 S 3 300 * 300 * 3.43  5 x 10 -4
Dimethylarsenic acid (CH 3 ) 2 AsO (OH) 200   5.79 829 to 22 o C
Lead arsenate PbHAsO 4 720   287 slightly soluble
Potassium arsenate KH 2 AsO 4 288     190 to 16 o C
Potassium arsenite 3 AsO 3       Soluble

 

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