Monopotassium arsenate

Monopotassium arsenate is the inorganic compound with the formula KH2AsO4. A white solid, this salt is used to prepared other arsenic-containing compounds, mainly pesticides. It is prepared by calcining arsenic oxide and potassium nitrate, followed by extraction with water.[1]

Monopotassium arsenate
Names
IUPAC name
Potassium dihydrogen arsorate
Other names
Macquer's salt
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.150 Edit this at Wikidata
EC Number
  • 232-065-8
UNII
UN number 1677
  • InChI=1S/AsH3O4.K/c2-1(3,4)5;/h(H3,2,3,4,5);/q;+1/p-1
    Key: GVPLVOGUVQAPNJ-UHFFFAOYSA-M
  • O[As](=O)(O)[O-].[K+]
Properties
AsH2KO4
Molar mass 180.032 g·mol−1
Appearance white solid
Density 2.867 g/cm3
Melting point 288 °C (550 °F; 561 K)
Hazards
GHS labelling:
GHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
Danger
H301, H331, H350, H410
P201, P202, P261, P264, P270, P271, P273, P281, P301+P310, P304+P340, P308+P313, P311, P321, P330, P391, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Relevant acid-base equilibria for aqueous solutions of this diprotic acid derived from arsenic acid are as follows:

H3AsO4 + H2O ⇌ H
2
AsO
4
+ H3O+  (pKa1 = 2.19)
H
2
AsO
4
+ H2O ⇌ HAsO2−
4
+ H3O+  (pKa2 = 6.94)
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References

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  1. ^ Grund, S. C.; Hanusch, K.; Wolf, H. U. "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2. ISBN 978-3527306732.{{cite encyclopedia}}: CS1 maint: multiple names: authors list (link)