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It oxidises readily in air to form arsenic trioxide and water, and analogous reactions take place with sulfur and selenium instead of oxygen. [3] Arsenic forms colorless, odorless, crystalline oxides As 2 O 3 ("white arsenic") and As 2 O 5 which are hygroscopic and readily soluble in water to form acidic solutions.
Despite the well known toxicity of arsenic, arsenic trioxide was used in traditional Chinese medicine, where it is known as pi-shuang (Chinese: 砒霜; pinyin: pīshuāng; lit. 'arsenic frost'). In homeopathy, it is called arsenicum album. Some discredited patent medicines, e.g., Fowler's solution, contained derivatives of arsenic oxide. [21]
It burns in oxygen to form arsenic trioxide and arsenic pentoxide, which have the same structure as the more well-known phosphorus compounds, and in fluorine to give arsenic pentafluoride. [31] Arsenic makes arsenic acid with concentrated nitric acid , arsenous acid with dilute nitric acid, and arsenic trioxide with concentrated sulfuric acid ...
Oxyarsenides or arsenide oxides are chemical compounds formally containing the group AsO, with one arsenic and one oxygen atom. The arsenic and oxygen are not bound together as in arsenates or arsenites, instead they make a separate presence bound to the cations (metals), and could be considered as a mixed arsenide-oxide compound.
In natural waters, the dissolved oxygen content is the main factor influencing reduction potential. Arsenates occur in oxygenated waters, which have a high pe, while arsenites are the main arsenic species in anoxic waters with a low pe. [16] A Pourbaix diagram shows the combined influence of pH and pe on arsenate speciation.
Nitric oxide (NO) is a part of cell regulation, including cellular metabolism, growth, division and death. [29] Nitric oxide (NO) reacts with reactive oxygen species to form peroxynitrite. [29] In cases of chronic arsenic exposure, the nitric oxide levels are depleted, due to the superoxide reactions. [29]
Arsenic pentoxide can be crystallized by heating As 2 O 3 under oxygen. This reaction is reversible: [3] As 2 O 5 ⇌ As 2 O 3 + O 2. Strong oxidizing agents such as ozone, hydrogen peroxide, and nitric acid convert arsenic trioxide to the pentoxide.
As reported in 1775, Carl Scheele reduced arsenic(III) oxide with zinc in the presence of acid. [11] This reaction is a prelude to the Marsh test. Alternatively, sources of As 3− react with protonic reagents to also produce this gas. Zinc arsenide and sodium arsenide are suitable precursors: [12]