Arsenic acid

Names
IUPAC name

Arsoric acid[1]

Other names

* Desiccant L-10
* Orthoarsenic acid
* Trihydrogen arsenate
* Zotox

Identifiers

CAS Number

* 7778-39-4 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:18231 Y

ChEMBL |

* ChEMBL2374288

ChemSpider |

* 229 Y

EC Number |

* 231-901-9

KEGG |

* C01478 Y

PubChem CID

* 234

RTECS number |

* CG0700000

UNII |

* N7CIZ75ZPN Y

UN number | 1553, 1554

InChI

* InChI=1S/AsH3O4/c2-1(3,4)5/h(H3,2,3,4,5) Y

Key: DJHGAFSJWGLOIV-UHFFFAOYSA-N Y

* InChI=1/AsH3O4/c2-1(3,4)5/h(H3,2,3,4,5)

Key: DJHGAFSJWGLOIV-UHFFFAOYAY

SMILES

* O[As+](O)([O-])O

Properties

Chemical formula

| H
3AsO

Molar mass | 141.942 g·mol−1
Appearance  | White translucent or colorless crystals, hygroscopic
Density | 2.5 g/cm3
Melting point |  35.5 °C (95.9 °F; 308.6 K)
Boiling point |  120 °C (248 °F; 393 K) decomposes

Solubility in water

| 16.7 g/(100 mL)
Solubility | soluble in ethanol
Vapor pressure | 55 hPa (50 °C)
Acidity (pKa)  | pKa1 = 2.19
pKa2 = 6.94
pKa3 = 11.5[2]
Conjugate base | Arsenate
Structure

Molecular shape

| Tetrahedral at arsenic atom
Hazards
Main hazards | Extremely toxic, carcinogenic, corrosive
GHS pictograms |
GHS Signal word | Danger

GHS hazard statements

| H301, H312, H314, H331, H350, H361, H410

GHS precautionary statements

| P201, P202, P260, P261, P264, P270, P271, P273, P280, P281, P301+310, P301+330+331, P302+352, P303+361+353, P304+340, P305+351+338, P308+313, P310, P311, P312, P321, P322, P330, P363, P391
NFPA 704 (fire diamond)  |

Flash point | Non-flammable
Lethal dose or concentration (LD, LC):

LD50 (median dose)

| 48 mg/kg (rat, oral)

6 mg/kg (rabbit, oral)

Related compounds

Other cations

| Sodium arsenate

Related compounds

* Arsenous acid
* Arsenic pentoxide
* Phosphoric acid

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Y verify (what is YN ?)
Infobox references

Tracking categories (test):

* SizeSet

Three bottles of arsenic acid from the Great Exhibition: impure, pure and distilled.

Arsenic acid or arsoric acid is the chemical compound with the formula H
3AsO
4, more descriptively written as AsO(OH)
3. This colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but is only found in solution, where it is largely ionized. Its hemihydrate form (2H
3AsO
4 * H2O) does form stable crystals. Crystalline samples dehydrate with condensation at 100 °C.[3]

## Contents

* 1 Properties
* 2 Preparation
* 2.1 Other methods
* 3 Applications
* 4 Safety
* 5 References

## Properties

It is a tetrahedral species of idealized symmetry C3v with As-O bond lengths ranging from 1.66 to 1.71 Å.[4]

Being a triprotic acid, its acidity is described by three equilibria:

3AsO
4 \+ H
2O ⇌ H
2AsO−
4 \+ [H
3O]+
, pKa1 = 2.19

2AsO−
4 \+ H
2O ⇌ HAsO2−
4 \+ [H
3O]+
, pKa2 = 6.94
HAsO2−
4 \+ H
2O ⇌ AsO3−
4 \+ [H
3O]+
, pKa3 = 11.5

These pKa values are close to those for phosphoric acid. The highly basic arsenate ion (AsO3−4) is the product of the third ionization. Unlike phosphoric acid, arsenic acid is an oxidizer, as illustrated by its ability to convert iodide to iodine.

## Preparation

Arsenic acid is prepared by treating arsenic trioxide with concentrated nitric acid. Dinitrogen trioxide is produced as a by-product.[5]

3 \+ 2 HNO
3 \+ 2 H
2O → 2 H
3AsO
4 \+ N

The resulting solution is cooled to give colourless crystals of the hemihydrate H
3AsO
4 * 0.5H2O (or 2H
3AsO
4 * H2O), although the dihydrate H
3AsO
4 * 2H2O is produced when crystallisation occurs at lower temperatures.[5]

### Other methods

Arsenic acid is slowly formed when arsenic pentoxide is dissolved in water, and when meta\- or pyroarsenic acid (H
4As

7) is treated with cold water. Arsenic acid can also be prepared directly from elemental arsenic by moistening it and treating with ozone.

2 As + 3 H
2O + 5 O
3 → 2 H
3AsO
4 \+ 5 O

## Applications

Commercial applications of arsenic acid are limited by its toxicity. It is a precursor to a variety of pesticides. It has found occasional use as a wood preservative, a broad-spectrum biocide, a finishing agent for glass and metal, and a reagent in the synthesis of some dyestuffs and organic arsenic compounds.[6]

## Safety

Arsenic acid is extremely toxic and carcinogenic, like all arsenic compounds. It is also corrosive. The -1">50 in rabbits is 6 mg/kg (0.006 g/kg).[7]

## References

1. ↑ "Arsenic acid". https://pubchem.ncbi.nlm.nih.gov/compound/234#section=IUPAC-Name&fullscreen=true.
2. ↑ Perrin, D. D., ed (1982). Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 11. ISBN 0-08-029214-3.
3. ↑ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
4. ↑ Lee, C.; Harrison, W. T. A. (2007). "Tetraethylammonium dihydrogenarsenate bis(arsenic acid) and 1,4-diazoniabicyclo[2.2.2]octane bis(dihydrogenarsenate) arsenic acid: hydrogen-bonded networks containing dihydrogenarsenate anions and neutral arsenic acid molecules". Acta Crystallographica C 63 (Pt 7): m308–m311. doi:10.1107/S0108270107023967. PMID 17609552. Bibcode: 2007AcCrC..63M.308L.
5. ↑ 5.0 5.1 G. Brauer, ed (1963). "Arsenic Acid". Handbook of Preparative Inorganic Chemistry. 1 (2nd ed.). New York: Academic Press. p. 601.
6. ↑ Minerals Yearbook, 2008, V. 1, Metals and Minerals. Government Printing Office. 2010. pp. 6–. ISBN 978-1-4113-3015-3. https://books.google.com/books?id=tL4hau707bwC&pg=SA6-PA10.
7. ↑ Grund, Sabina C.; Hanusch, Kunibert; Wolf, Hans Uwe (2008). "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a03_113.pub2. ISBN 978-3527306732.

* v
* t
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Hydrogen compounds

* H3AsO3
* H3AsO4
* HArF
* HAt
* HSO3F
* HBF4
* HBr
* HBrO
* HBrO2
* HBrO3
* HBrO4
* HCl
* HClO
* HClO2
* HClO3
* HClO4
* HCN
* HCNO
* H2CrO4/H2Cr2O7
* H2CO3
* H2CS3
* HF
* HFΟ
* HI
* HIO
* HIO2
* HIO3
* HIO4
* HMnO4
* H2MoO4
* HNC
* NaHCO3
* HNCO
* HNO
* HNO2
* HNO3
* H2N2O2
* HNO5S
* H3NSO3
* H2O
* H2O2
* H2O3
* H3PO2
* H3PO3
* H3PO4
* H4P2O7
* H5P3O10
* H2PtCl6
* H2S
* H2S2
* H2Se
* H2SeO3
* H2SeO4
* H4SiO4
* H2SiF6
* HSCN
* HNSC
* H2SO3
* H2SO4
* H2SO5
* H2S2O3
* H2S2O6
* H2S2O7
* H2S2O8
* CF3SO3H
* H2Te
* H2TeO3
* H6TeO6
* H4TiO4
* H2Po
* HCo(CO)4

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*[CID]: Compound ID
*[H301]: Toxic if swallowed
*[H312]: Harmful in contact with skin
*[H314]: Causes severe skin burns and eye damage
*[H331]: Toxic if inhaled
*[H350]: May cause cancer
*[H361]: Suspected of damaging fertility or the unborn child
*[H410]: Very toxic to aquatic life with long lasting effects
*[P201]: Obtain special instructions before use
*[P202]: Do not handle until all safety precautions have been read and understood
*[P260]: Do not breathe dust/fume/gas/mist/vapours/spray
*[P261]: Avoid breathing dust/fume/gas/mist/vapours/spray
*[P264]: Wash … thoroughly after handling
*[P270]: Do not eat, drink or smoke when using this product
*[P271]: Use only outdoors or in a well-ventilated area
*[P273]: Avoid release to the environment
*[P280]: Wear protective gloves/protective clothing/eye protection/face protection
*[P281]: Use personal protective equipment as required
*[P301+310]: IF SWALLOWED: Immediately call a POISON CENTER or doctor/physician
*[P301+330+331]: IF SWALLOWED: Rinse mouth. Do NOT induce vomiting
*[P302+352]: IF ON SKIN: Wash with soap and water
*[P303+361+353]: IF ON SKIN (or hair): Remove/Take off immediately all contaminated clothing. Rinse skin with water/shower
*[P304+340]: IF INHALED: Remove victim to fresh air and keep at rest in a position comfortable for breathing
*[P305+351+338]: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing
*[P308+313]: IF exposed or concerned: Get medical advice/attention
*[P310]: Immediately call a POISON CENTER or doctor/physician
*[P311]: Call a POISON CENTER or doctor/physician
*[P312]: Call a POISON CENTER or doctor/physician if you feel unwell
*[P321]: Specific treatment (see … on this label)
*[P322]: Specific measures (see … on this label)
*[P330]: Rinse mouth
*[P363]: Wash contaminated clothing before reuse
*[P391]: Collect spillage
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