Mercury(I) sulfate explained

Mercury(I) sulfate, commonly called mercurous sulphate (UK) or mercurous sulfate (US) is the chemical compound Hg₂SO₄.^[1] Mercury(I) sulfate is a metallic compound that is a white, pale yellow or beige powder.^[2] It is a metallic salt of sulfuric acid formed by replacing both hydrogen atoms with mercury(I). It is highly toxic; it could be fatal if inhaled, ingested, or absorbed by skin.

Structure

In the crystal, mercurous sulfate is made up of Hg₂²⁺ center with an Hg-Hg distance of about 2.50 Å. The SO₄²⁻ anions form both long and short Hg-O bonds ranging from 2.23 to 2.93 Å.^[3]

Focusing on the shorter Hg-O bonds, the Hg – Hg – O bond angle is 165°±1°.^{[4] [5]}

Preparation

One way to prepare mercury(I) sulfate is to mix the acidic solution of mercury(I) nitrate with 1 to 6 sulfuric acid solution:,^{[6] [7]}

It can also be prepared by reacting an excess of mercury with concentrated sulfuric acid:^[6]

Use in electrochemical cells

Mercury(I) sulfate is often used in electrochemical cells.^{[8] [9] [10]} It was first introduced in electrochemical cells by Latimer Clark in 1872,^[11] It was then alternatively used in Weston cells made by George Augustus Hulett in 1911.^[11] It has been found to be a good electrode at high temperatures above 100 °C along with silver sulfate.^[12]

Mercury(I) sulfate has been found to decompose at high temperatures. The decomposition process is endothermic, and it occurs between 335 °C and 500 °C.

Mercury(I) sulfate has unique properties that make the standard cells possible. It has a rather low solubility (about one gram per liter); diffusion from the cathode system is not excessive; and it is sufficient to give a large potential at a mercury electrode.^[13]

Notes and References

1. Intermediate Inorganic Chemistry by J. W. Mellor, published by Longmans, Green and Company, London, 1941, page 388
2. Web site: Mercurous Sulfate | 7783-36-0.
3. Preparation and Characterization of Dimercury(I)Monofluorophosphate(V), Hg₂PO₃F: Crystal Structure, Thermal Behavior, Vibrational Spectra, and Solid-State ³¹P and ¹⁹F NMR Spectra. Matthias Weil . Michael Puchberger . Enrique J. Baran . Inorg. Chem.. 2004. 43. 26. 8330–8335. 10.1021/ic048741e. 15606179.
4. Dorm, E.. 1969. Structural Studies on Mercury(I) Compounds. VI. Crystal Structure of Mercury(I) Sulfate and Selenate. Acta Chemica Scandinavica. 23. 1607–15. 10.3891/acta.chem.scand.23-1607. free.
5. 10.1107/S1600536814011155. Crystal structure of Hg2SO4– a redetermination. 2014. Weil. Matthias. Acta Crystallographica Section E. 70. 9. i44. 25309168. 4186147.
6. https://books.google.com/books?id=VrTVAAAAMAAJ&q=%22mercury%28I%29+sulfate%22+prepared Google Books result
7. Mercurous Sulphate, cadmium sulphate, and the cadmium cell. by Hulett G. A. The physical review.1907. p.19.
8. "Influence of Microstucture on the Charge Storage Properties of Chemically Synthesized Manganese Dioxide" by Mathieu Toupin, Thiery Brousse, and Daniel Belanger. Chem. Mater. 2002, 14, 3945–3952
9. "Electromotive Force Studies of Cell, Cd_xHg_y | CdSO₄,(m) I Hg₂SO₄, Hg, in Dioxane-Water Media" by Somesh Chakrabarti and Sukumar Aditya. Journal of Chemical and Engineering Data, Vol.17, No. 1, 1972
10. "Characterization of Lithium Sulfate as an Unsymmetrical-Valence Salt Bridge for the Minimization of Liquid Junction Potentials in Aqueous – Organic Solvent Mixtures" by Cristiana L. Faverio, Patrizia R. Mussini, and Torquato Mussini. Anal. Chem. 1998, 70, 2589–2595
11. "George Augustus Hulett: from Liquid Crystals to Standard Cell" by John T. Stock. Bull. Hist. Chem. Volume 25, Number 2, 2000, p.91-98
12. Lietzke . M. H. . Stoughton . R. W. . The Behavior of the Silver—Silver Sulfate and the Mercury—Mercurous Sulfate Electrodes at High Temperatures 1 . Journal of the American Chemical Society . November 1953 . 75 . 21 . 5226–5227 . 10.1021/ja01117a024.
13. "Sulphates of Mercury and Standard Cells." by Elliott, R. B. and Hulett, G. A. The Journal of Physical Chemistry 36.7 (1932): 2083–2086.