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Arsenous acid, also known as arsenious acid, is the hydrolyzed form of arsenic trioxide
Arsenic trioxide

Arsenic trioxide is the most important commercial compound of arsenic, and the main starting material for arsenic chemistry. It is the highly toxic byproduct of certain kinds of ore processing, for example gold mining....
 and has the formula As(OH)3.






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Arsenous Acid 2d
Arsenous Acid 3d Vdw
Arsenous acid, also known as arsenious acid, is the hydrolyzed form of arsenic trioxide
Arsenic trioxide

Arsenic trioxide is the most important commercial compound of arsenic, and the main starting material for arsenic chemistry. It is the highly toxic byproduct of certain kinds of ore processing, for example gold mining....
 and has the formula As(OH)3. As(OH)3 occurs in aqueous solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
s and has not been isolated as a pure material, although this fact does not detract from the significance of As(OH)3.

Properties

The molecular weight of arsenous acid, is 125.94 g/mol. As(OH)3 is a pyramidal molecule consisting of three hydroxyl
Hydroxide

In chemistry, hydroxide is the name for the Diatomic molecule anion OH-, consisting of oxygen and hydrogen atoms, usually derived from the Dissociation of a base ....
 groups connected by single bonds to arsenic. The 1H NMR
NMR

NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear Magnetic Resonance.* NMR Spectroscopy.* Proton NMR.* Carbon-13 NMR....
 spectrum of arsenous acid solutions consists of a single signal consistent with the molecule's high symmetry. In contrast, the nominally related phosphorus
Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
 species H3PO3 mainly adopts the structure HPO(OH)2; P(OH)3 is a very minor equilibrium component of such solutions. The differing behaviors of the As and P compounds reflect a trend whereby high oxidation states are more stable for lighter members of main group elements than their heavier congeners.

As(OH)3 is a weak acid
Weak acid

A weak acid is an acid that dissociates incompletely and does not release all of its hydrogens in a solution i.e it does not completely donate all of its protons....
 with a pKa of 9.2.

Reactions

The preparation of As(OH)3 involves a slow hydrolysis
Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
 of arsenic trioxide
Arsenic trioxide

Arsenic trioxide is the most important commercial compound of arsenic, and the main starting material for arsenic chemistry. It is the highly toxic byproduct of certain kinds of ore processing, for example gold mining....
 in water. Addition of base
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
 converts arsenous acid to the arsenite ions
Arsenite

In chemistry an arsenite is a chemical compound containing an arsenic oxoanion where arsenic has oxidation state +3. Examples of arsenites include sodium arsenite which contains a polymeric linear anion, [AsO2-]n, silver arsenite, Ag3AsO3, which contains the trigonal, ArsenicOxygen3<...
 [AsO(OH)2]-, [AsO2(OH)]2-, and [AsO3]3-. Reactions attributed to aqueous arsenic trioxide
Arsenic trioxide

Arsenic trioxide is the most important commercial compound of arsenic, and the main starting material for arsenic chemistry. It is the highly toxic byproduct of certain kinds of ore processing, for example gold mining....
 are due to arsenous acid and its conjugate bases.

Toxicology

Arsenic containing compounds are highly toxic and carcinogenic. The anhydride form of arsenous acid, arsenic trioxide
Arsenic trioxide

Arsenic trioxide is the most important commercial compound of arsenic, and the main starting material for arsenic chemistry. It is the highly toxic byproduct of certain kinds of ore processing, for example gold mining....
, is used as a herbicide
Herbicide

A herbicide is used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant hormones....
, pesticide
Pesticide

A pesticide is a substance or mixture of substances used to kill a pest .A pesticide may be a chemical substance, biological agent , antimicrobial, disinfectant or device used against any pest ....
, and rodenticide.

Literary References

Arsenious acid is identifed through the microscope as a "crystalline particle" by the fictitious Dr. Thorndyke following isolation from the grainy arrowroot
Arrowroot

Arrowroot, or obedience plant , is a large perennial plant herb of genus Maranta found in rainforest habitats. Arrowroot is also the name of the edible starch from the rhizomes of West Indian arrowroot....
 breakfast of a concerned Mr. Barton in the Moabite Cypher case.

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