Magnesium arsenate

Crystal structure
	__ Mg __ As __ O
Crystal system	tetragonal
Space group	I 4 2 d (No. 122)
Lattice parameters	a = 6.783 Å , c = 18.963 Å
General
Surname	Magnesium arsenate
Ratio formula	Mg 3 (AsO 4 ) 2
Brief description	white crystal or powder
External identifiers / databases
PubChem	24943
Wikidata	Q4337135
properties
Molar mass	350.75 g mol −1
Physical state	firmly
density	2.60 g cm −3 (octahydrate); 1.78 g cm −3 (22 hydrate);
solubility	practically insoluble in water
safety instructions
H and P phrases	H: 301-331-350-410
	P: ?
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Magnesium arsenate , Mg ₃ (AsO ₄ ) ₂ is the magnesium salt of arsenic acid .

Occurrence

Magnesium arsenate octahydrate naturally occurs as a mineral hornsite .

Extraction and presentation

The octahydrate can be obtained by mixing the aqueous solutions of magnesium sulfate , sodium monohydrogen arsenate and sodium bicarbonate .

{\ displaystyle {\ ce {MgSO4 + Na2HAsO4 -> Mg3 (AsO4) 2 * 8H2O + Na2SO4}}}

The heptahydrate is formed when sodium dihydrogen arsenate is used in place of the monohydrogen salt in the above preparation. The decahydrate is formed when potassium or ammonium magnesium orthoarsenate is digested with water for several hours. In the dehydration, hydrates with a content of 6, 5, 3 and 2 can be obtained.

The anhydrate can be obtained from a melt of magnesium carbonate and arsenic (V) oxide at 1450 ° C.

properties

Crystal structure of magnesium arsenate (viewed from the C side).

Magnesium arsenate is a white crystal or powder. It is not flammable and practically insoluble in water. From 100 ° C, water of crystallization is split off, which increases with higher temperature. The crystal structure of the anhydrate is tetragonal (a = 6.783 Å, c = 18.963 Å, Z = 6 and space group I 4 2 d (space group no. 122) . The structure contains two different AsO ₄ groups with average bond lengths of 1.678 and 1.678 respectively. 1.690 Å. Two of the three magnesium ions are octahedrally coordinated, and the third one takes the place of symmetry 4. The anhydrous salt decomposes when heated above 1100 ° C in a vacuum, with magnesium oxide , arsenic (III) oxide and oxygen being formed. Template: room group / 122

use

Magnesium arsenate is used as a red fluorescent phosphor for the lining of advertising tubes. It was also used as an insecticide .

toxicology

When inhaling or ingesting the compound is toxic. The substance is considered to be carcinogenic.

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g Entry on magnesium arsenate in the GESTIS substance database of the IFA , accessed on February 6, 2019 (JavaScript required)
↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry arsenic compounds, with the exception of those named in this appendix in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA) on February 6, 2019. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ ^a ^b ^c ^d Richard C. Ropp: Encyclopedia of the Alkaline Earth Compounds . Newnes, 2012, ISBN 0-444-59553-8 , pp. 299 ( limited preview in Google Book search).
↑ G. Bünemann, W. Klosterkötter: Toxicological and industrial hygiene testing of a phosphor made of magnesium arsenate . In: International Archive for Industrial Pathology and Industrial Hygiene . tape 20 , no. 1 , January 1963, p. 21-35 , doi : 10.1007 / BF00370045 .
↑ Dale L. Perry: Handbook of Inorganic Compounds . CRC Press , 1995, ISBN 978-0-8493-8671-8 , pp. 9 ( limited preview in Google Book search).

[GESTIS-1] ↑ ^a ^b ^c ^d ^e ^f ^g Entry on magnesium arsenate in the GESTIS substance database of the IFA , accessed on February 6, 2019 (JavaScript required)

[CLP_100.240.769-2] Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry arsenic compounds, with the exception of those named in this appendix in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA) on February 6, 2019. Manufacturers or distributors can expand the harmonized classification and labeling .

[Richard_C._Ropp-3] Richard C. Ropp: Encyclopedia of the Alkaline Earth Compounds . Newnes, 2012, ISBN 0-444-59553-8 , pp. 299 ( limited preview in Google Book search).

[DOI10.1007/BF00370045-4] G. Bünemann, W. Klosterkötter: Toxicological and industrial hygiene testing of a phosphor made of magnesium arsenate . In: International Archive for Industrial Pathology and Industrial Hygiene . tape 20 , no. 1 , January 1963, p. 21-35 , doi : 10.1007 / BF00370045 .

[Dale_L._Perry-5] Dale L. Perry: Handbook of Inorganic Compounds . CRC Press , 1995, ISBN 978-0-8493-8671-8 , pp. 9 ( limited preview in Google Book search).