Magnesium chromate

Structural formula
	No drawing available
General
Surname	Magnesium chromate
other names	Magnesium (II) chromium (VI) oxide
Molecular formula	Mg [CrO 4 ]
Brief description	yellow solid (pentahydrate); orange-yellow solid (heptahydrate);
External identifiers / databases
EC number	236-540-0
ECHA InfoCard	100.033.204
Wikidata	Q15634245
properties
Molar mass	140.299 g mol −1 (pure substance); 230.375 g mol −1 (pentahydrate); 266.406 g mol −1 (heptahydrate); 338.466 g mol −1 (undecahydrate);
Physical state	firmly
density	4.18 g cm −3
Melting point	1200–1250 ° C (decomposition)
solubility	easy in water (600 g l −1 at 18 ° C)
safety instructions
H and P phrases	H: 350i-317-410
	P: ?
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Magnesium chromate is a salt made from magnesium and chromic acid . The pentahydrate, heptahydrate and undecahydrate are known.

Extraction and presentation

Magnesium chromate heptahydrate can be prepared from a solution of Mg (OH) ₂ and chromic acid.

The heptahydrate can at 335 ° C for anhydrate decomposed be.

The anhydrate can be obtained by reacting chromium (III) oxide with magnesium oxide and oxygen at high pressure.

properties

The decomposition of magnesium chromate heptahydrate takes place in four stages.

1st stage in the range 33–58 ° C

${\ displaystyle {\ ce {Mg [CrO4] * 7H2O -> Mg [CrO4] * 5H2O + 2H2O}}}$

2nd stage in the range 127–150 ° C

${\ displaystyle {\ ce {Mg [CrO4] * 5H2O -> Mg [CrO4] * 1.5H2O + 3.5H2O}}}$

3rd stage in the range 196-215 ° C

${\ displaystyle {\ ce {Mg [CrO4] * 1.5H2O -> Mg [CrO4] * H2O + 0.5H2O}}}$

4th stage at 335 ° C

${\ displaystyle {\ ce {Mg [CrO4] * H2O -> Mg [CrO4] + H2O}}}$

The anhydrous magnesium chromate decomposes at over 600 ° C. Magnesium chromate comes in two modifications before the α and the β modification. The α modification crystallizes orthorhombically in the Cr [VO ₄ ] structure ( lattice parameters : a = 549.7, b = 836.8, c = 614.7 pm ) and the β modification in the Co [MoO ₄ ] - Structure (lattice parameters: a = 995, b = 916, c = 675.9 pm and β = 103.68 °). A yellow magnesium chromate-Undecahydrat (Mg [CrO ₄ ] ∙ 11H ₂ O) is also known and crystallized isotypic to Meridianiit (Mg [SO ₄ ] ∙ 11H ₂ O), in the triclinic space group P 1 (space group no. 2) with the lattice constants a = 677.21 (18), b = 691.7 (2), c = 1741.0 (5) pm, α = 88.21 (2) °, β = 89.43 (2) ° and γ = 62.768 (18) ° with two formula units per unit cell . Template: room group / 2

use

Magnesium chromate occurs when chromating of magnesium alloys and serves as corrosion protection .

safety

Magnesium chromate is classified as a carcinogen .

Individual evidence

↑ ^a ^b ^c ^d ^e Jane E. Macintyre: Dictionary of Inorganic Compounds . CRC Press, 1992, ISBN 978-0-412-30120-9 , pp. 3076 ( limited preview in Google Book search).
↑ VN Titov: The metastable phase magnesium chromate (Mg ₂ Cr ₂ O ₅ ) . In: Izvestiya Akademii Nauk SSSR, Neorganicheskie Materialy . tape V24 , no. 11 , 1988, pp. 1934-1935 .
^ AE Hill, GC Soth, JE Ricci: The Systems Magnesium Chromate — Water and Ammonium Chromate — Water from 0 to 75 ° . In: J. Am. Chem. Soc. tape 62 , no. 8 , 1940, p. 2131-2134 , doi : 10.1021 / ja01865a059 .
↑ ^a ^b Entry on magnesium chromate in the GESTIS substance database of the IFA , accessed on May 13, 2020(JavaScript required) .
↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the indicated labeling it falls under the group entry Chromium (VI) compounds, with the exception of barium chromate and compounds that are listed separately in this appendix in Classification and Labeling inventory of the European Chemicals Agency (ECHA), accessed on May 13, 2020. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ ^a ^b ^c ^d Tadashi Nisino, Mogi Konasayoshi, Hiroshi Kano: Thermal decomposition of magnesium chromate . In: Journal of the Ceramic Association . tape 71 , no. 812 , 1963, pp. 159-163 , doi : 10.2109 / jcersj1950.71.812_159 .
↑ ^a ^b O. Müller, WB White, R. Roy: X-ray diffraction study of the chromates of nickel, magnesium and cadmium . In: Z. Kristallogr. tape 130 , 1969, p. 112-120 , doi : 10.1524 / zkri.1969.130.16.112 .
↑ AD Fortes, IG Wood, JG Matthias: MgSO ₄∙ 11 H ₂ O and MgCrO ₄∙ 11 H ₂ Obased on time-of-flight neutron single-crystal Laue data . In: Acta Crystallogr. C69, 2013, p. 324-329 , doi : 10.1107 / S0108270113005751 .
↑ AD Fortes, IG Wood: X-ray powder diffraction analysis of a new magnesium chromate hydrate, MgCrO ₄∙ 11 (H ₂ O) . In: Powder Diffraction . tape 27 , no. 1 , 2012, p. 8-11 , doi : 10.1017 / S088571561200005X .
↑ Hubert Gräfen, VDI-Gesellschaft Werkstofftechnik: Lexikon Werkstofftechnik, corrected reprint . Springer-Verlag, 2013, ISBN 978-3-642-51732-7 , pp. 130 ( limited preview in Google Book search).

[Jane_E._Macintyre-1] Jane E. Macintyre: Dictionary of Inorganic Compounds . CRC Press, 1992, ISBN 978-0-412-30120-9 , pp. 3076 ( limited preview in Google Book search).

[2] VN Titov: The metastable phase magnesium chromate (Mg ₂ Cr ₂ O ₅ ) . In: Izvestiya Akademii Nauk SSSR, Neorganicheskie Materialy . tape V24 , no. 11 , 1988, pp. 1934-1935 .

[3] AE Hill, GC Soth, JE Ricci: The Systems Magnesium Chromate — Water and Ammonium Chromate — Water from 0 to 75 ° . In: J. Am. Chem. Soc. tape 62 , no. 8 , 1940, p. 2131-2134 , doi : 10.1021 / ja01865a059 .

[GESTIS-4] Entry on magnesium chromate in the GESTIS substance database of the IFA , accessed on May 13, 2020(JavaScript required) .

[CLP_100.240.768-5] Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the indicated labeling it falls under the group entry Chromium (VI) compounds, with the exception of barium chromate and compounds that are listed separately in this appendix in Classification and Labeling inventory of the European Chemicals Agency (ECHA), accessed on May 13, 2020. Manufacturers or distributors can expand the harmonized classification and labeling .

[:0-6] Tadashi Nisino, Mogi Konasayoshi, Hiroshi Kano: Thermal decomposition of magnesium chromate . In: Journal of the Ceramic Association . tape 71 , no. 812 , 1963, pp. 159-163 , doi : 10.2109 / jcersj1950.71.812_159 .

[:1-7] O. Müller, WB White, R. Roy: X-ray diffraction study of the chromates of nickel, magnesium and cadmium . In: Z. Kristallogr. tape 130 , 1969, p. 112-120 , doi : 10.1524 / zkri.1969.130.16.112 .

[8] AD Fortes, IG Wood, JG Matthias: MgSO ₄∙ 11 H ₂ O and MgCrO ₄∙ 11 H ₂ Obased on time-of-flight neutron single-crystal Laue data . In: Acta Crystallogr. C69, 2013, p. 324-329 , doi : 10.1107 / S0108270113005751 .

[9] AD Fortes, IG Wood: X-ray powder diffraction analysis of a new magnesium chromate hydrate, MgCrO ₄∙ 11 (H ₂ O) . In: Powder Diffraction . tape 27 , no. 1 , 2012, p. 8-11 , doi : 10.1017 / S088571561200005X .

[Hubert_Gräfen,_VDI-Gesellschaft_Werkstofftechnik-10] Hubert Gräfen, VDI-Gesellschaft Werkstofftechnik: Lexikon Werkstofftechnik, corrected reprint . Springer-Verlag, 2013, ISBN 978-3-642-51732-7 , pp. 130 ( limited preview in Google Book search).