Chevreul's salt
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| Names | |
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| IUPAC name
Copper(I, II) sulfite dihydrate | |
| Other names
Chevreul's salt | |
| Identifiers | |
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3D model (JSmol) |
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| ChemSpider | |
PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| Cu2SO3·CuSO3·2H2O | |
| Molar mass | 386.78 g·mol−1 |
| Appearance | brick red powder |
| Density | 3.57 g/cm3 |
| Solubility | aqueous ammonia |
| 3.71×10−6 emu/g[2] | |
| Thermal conductivity | 0.1 kW/(cm·K)[3] |
| Structure[3] | |
| monoclinic | |
| P21/n | |
a = 5.5671 Å, b = 7.7875 Å, c = 8.3635 Å α = 90°, β = 91.279°, γ = 90° | |
Lattice volume (V) |
362.5 Å3 |
| Thermochemistry[3] | |
Heat capacity (C) |
0.62 J·cm-3·K-1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Chevreul's salt (copper(I,II) sulfite dihydrate, Cu2SO3·CuSO3·2H2O or Cu3(SO3)2·2H2O), is a copper salt which was prepared for the first time by a French chemist Michel Eugène Chevreul in 1812. Its unusual property is that it contains copper in both of its common oxidation states, making it a mixed-valence complex. It is insoluble in water and stable in air.[4] What was known as Rogojski's salt is a mixture of Chevreul's salt and metallic copper.[5]
Properties
The infrared spectrum of Chevreul's salt contains strong bands with maxima at 473, 632 cm−1, medium ones at 915, 980, and 1025 cm−1, and a weak band at 860 cm−1.[5] The band at 980 cm−1 is due to symmetric stretch of the sulfite group, 632 cm−1 is due to symmetric bend, 915 cm−1 is due to asymmetric stretch, and 473 cm−1 is due to asymmetric bend. The absence of splitting in these bands indicates that the sulfite group is not distorted by the other components in the compound.[5]
The optical reflectance spectrum shows absorption around 425 nm with a shoulder to 500 nm. This is due to a cuprous sulfite chromophore. An absorption peaking at 785 nm with a shoulder to 1000 nm, in the near infrared, is due to Jahn-Teller splitting in cupric ions. Maximum reflectance is around 650 nm in the red part of the spectrum.[3]
In the infrared range the band gap is 0.85 eV.[6]
Chevreul's salt is a representative member of an isomorphic series of double salts with formulae Cu2SO3·FeSO3·2H2O, Cu2SO3·MnSO3·2H2O, and Cu2SO3·CdSO3·2H2O. The properties of these salts show the effect of ionic radius and ion hardness.[7] Another analogue, Cu2SO3·NiSO3·2H2O, is brick-red in colour. It is made by bubbling sulfur dioxide through a nickel sulfate, copper sulfate mixed solution, heating to 80 °C (176 °F) and changing pH to 3.5 to precipitate the salt.[8]
In Chevreul's salt crystals there are two environments for copper. The +1 oxidation state copper is in a distorted tetrahedral space surrounded by three oxygens and a sulfur atom. The +2 oxidation state copper (or other metal in the isomorphic series) is in a distorted octahedral coordination surrounded by four oxygen atoms and two water molecules.[6]
The X-ray photoelectron spectrum of Chevreul's salt shows peaks at 955.6, 935.8, 953.3 and 943.9 eV that correspond to Cu(II) 2p1/2, 2p3/2, Cu(I) 2p1/2, 2p3/2. There are also secondary peaks for copper at 963.7, and 943.9 eV. Sulfur 2p causes a peak at 166.7 eV and oxygen 1s causes a spike at 531.8 eV.[9]
Preparation
Chevreul's salt is prepared by treating aqueous copper(II) sulfate (CuSO4) with a solution of potassium metabisulfite (K2S2O5). The solution changes colour from blue to green immediately. The identity of the green species is unknown. Heating this solution produces a reddish solid precipitate:[10]
- 3 CuSO4 + 4 K2S2O5 + 3 H2O → Cu3(SO3)2·2H2O + 4 K2SO4 + 4 SO2 + H2SO4
It has also been prepared by heating a solution of CuSO4 with sodium hydrogen sulfite (NaHSO3) at 60–70 °C (140–158 °F) for 3 hours, and by saturating a solution of CuSO4 with sulfur dioxide (SO2) at ambient temperature.[11][3]
When sodium ions are present in the solutions that form the salt, sodium can substitute for some of the copper(I), as the ions have the same charge and similar sizes.[3]
Reactions
Chevreul's salt exhibits properties of both copper(I) and copper(II). Hydrochloric acid produces a white solid of copper(I) chloride. If too much acid is added, the precipitate dissolves. If an ammonia solution is added to the product, it is dissolved and a deep blue color appears - the presence of [Cu(NH3)4]2+ complex.[5]
On heating in an inert atmosphere it is stable to 200 °C (392 °F). It gives off water and sulfur dioxide to give CuSO4·Cu2O and CuSO4·2CuO. At 850 °C (1,560 °F) cupric oxide (CuO) is formed and from 900 to 1,100 °C (1,650 to 2,010 °F) cuprous oxide (Cu2O) appears. Heating in air or oxygen yields cupric sulfate (CuSO4), cupric sulfite (CuSO3), and ultimately CuO [3][12]
Application
Chevreul's salt is used in a hydrometallurgical process to extract copper from ore. Firstly the ore is oxidised, then extracted with an ammonium sulfate-ammonia solution. This is then injected with sulfur dioxide resulting in the precipitation of Chevreul's salt. pH must be between 2 and 4.5 for the precipitation to take place.[7]
Chevreul's salt is formed as a corrosion product on copper metal in the presence of humid air contaminated with sulfur dioxide. When first formed the salt has an unstable orthorhombic form with a = 5.591 Å, b = 7.781 Å and c = 8.356 Å, which changes to the normal monoclinic form over a month, or faster when heated.[13]
References
- ↑ Masson, M. R.; Lutz, H. D.; Engelen, B. (2013). Sulfites, Selenites & Tellurites. Elsevier. pp. 262–266. ISBN 9781483286433.
- ↑ Pardasani, R. T.; Pardasani, P. (2017). "Magnetic properties of Chevreul's salt, a mixed valence copper sulfite". Magnetic Properties of Paramagnetic Compounds. Springer, Berlin, Heidelberg. p. 181. doi:10.1007/978-3-662-53974-3_88. ISBN 9783662539736.
- 1 2 3 4 5 6 7 Silva, Luciana A. da; Andrade, Jailson B. de (April 2004). "Isomorphic series of double sulfites of the Cu2SO3.MSO3.2H2O (M = Cu, Fe, Mn, and Cd) Type: a review". Journal of the Brazilian Chemical Society. 15 (2): 170–177. doi:10.1590/S0103-50532004000200003.
- ↑ Chevreul, M. E. (1812). "Propriétés du sulfte de cuivre". Annales de Chimie. 83: 187.
- 1 2 3 4 Dasent, W.E.; Morrison, D. (June 1964). "The sulphites of unipositive copper". Journal of Inorganic and Nuclear Chemistry. 26 (6): 1122–1125. doi:10.1016/0022-1902(64)80274-8.
- 1 2 Kierkegaard, Peder; Nyberg, Birgit (July 1965). "The crystal structure of Cu2SO3.CuSO3.2H2O". Acta Chemica Scandinavica. 19 (1–3): 2189–99. doi:10.3891/acta.chem.scand.19-2189.
- 1 2 Çalban, Turan; Çolak, Sabri; Yeşilyurt, Murat (March 2006). "Statistical modeling of Chevreul's salt recovery from leach solutions containing copper". Chemical Engineering and Processing: Process Intensification. 45 (3): 168–174. Bibcode:2006CEPPI..45..168C. doi:10.1016/j.cep.2005.06.008.
- ↑ Chalaya, E. A.; Tyurin, A. G.; Vasekha, M. V.; Biryukov, A. I. (17 August 2016). "Synthesis and properties of double copper(I)–nickel(II) sulfite". Russian Journal of General Chemistry. 86 (7): 1545–1551. doi:10.1134/S1070363216070021. S2CID 99729125.
- ↑ Brant, Patrick; Fernando, Quintus (January 1978). "The X-ray photoelectron spectrum of a mixed valence compound of copper". Journal of Inorganic and Nuclear Chemistry. 40 (2): 235–237. doi:10.1016/0022-1902(78)80117-1.
- ↑ "Molecule of the Week Archive - Chevreul's salt". www.acs.org. American Chemical Society. 24 July 2023. Retrieved 4 July 2026.
- ↑ Inoue, Motomichi; Grijalva, Heriberto; Inoue, Michiko B; Fernando, Quintus (November 1999). "Spectroscopic and magnetic properties of Chevreul's salt, a mixed valence copper sulfite Cu3(SO3)2·2H2O". Inorganica Chimica Acta. 295 (1): 125–127. doi:10.1016/S0020-1693(99)00333-3.
- ↑ Silva, L.A.; Matos, J.R.; de Andrade, J.B. (August 2000). "Synthesis, identification and thermal decomposition of double sulfites like Cu2SO3·MSO3·2H2O (M=Cu, Fe, Mn or Cd)". Thermochimica Acta. 360 (1): 17–27. doi:10.1016/S0040-6031(00)00525-6.
- ↑ Giovannelli, G.; Natali, S.; Zortea, L.; Bozzini, B. (April 2012). "An investigation into the surface layers formed on oxidised copper exposed to SO2 in humid air under hypoxic conditions". Corrosion Science. 57: 104–113. doi:10.1016/j.corsci.2011.12.028.