Arsenic was already known by scientist in the 17th century. At that time, this substance, that is now - one of the elements of the periodic table, was known as a strong poison.
Arsenic is substance that are chemical compounds are strong poisons too. For example, salts containing arsenic are very toxic and at a dose 0.1 gram is deadly poisonous for humans.
The experience of mankind knows that there are substances that are poisonous in large doses, but beneficial in small doses. These properties have some arsenic compounds. For example, arsenic oxide As2O3 – a substance is toxic, but the dosage is not more than 5 mg, its even prescribed to improve the health of the person. It has a tonic effect.
Perhaps, all once treat a teeth. In order to do the treatment is painless, required to neutralize the nervous perception. And the arsenic helps here too! As arsenic acid the arsenic enters to the tooth together with the paste and neutralizes the nerve. Snake also is the symbol of arsenic on the medical emblem!
Arsenic is very popular among those who wish to prepare some poison. But modern methods can easily detect even a tiny dose of arsenic, if it was used, for example, in food. To detect the presence of arsenic is possible with analytical chemistry – special chemical reactions, are able to identify individual chemical element and complex substances in a variety of chemical environments.
How to detect arsenic
How to detect arsenic, was known in the mid of 19th century. As a result of chemical reactions produced the recovery of arsenic.
As2O3+6Zn+6H2SO4=2AsH3+ 6ZnSO4+3H2O
One of the products of this reaction is a gaseous substance - arsine (AsH), that when heated to 400o decays into hydrogen and metallic arsenic. This chemical reaction allows to detect the concentration of arsenic even when the content is 0.001 mg.
Another reaction, able to detect arsenic from chemical compounds - is the reaction with silver nitrate. The reaction takes place:
HAsO2+3AgNO3+H2O=Ag3AsO3+3HNO3.
Arsenic is determined with presence of yellow cloudy solution Ag3AsO3.