Mercury(I) sulfate, commonly called mercurous sulphate ( UK) or mercurous sulfate ( US) is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

Hg₂SO₄. Mercury(I) sulfate is a metallic compound that is a white, pale yellow or beige powder. 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. Focusing on the shorter Hg-O bonds, the Hg – Hg – O bond angle is 165°±1°.

Preparation

One way to prepare mercury(I) sulfate is to mix the acidic solution of

mercury(I) nitrate Mercury(I) nitrate is a inorganic compound, a salt of mercury and nitric acid with the formula Hg2(NO3)2. A yellow solid, the compound is used as a precursor to other complexes of Hg22+ complexes.The structure of the hydrate has been determined b ...

with 1 to 6 sulfuric acid solution:,Google Books result
accessed 11 December 2010 :Hg₂(NO₃)₂ + H₂SO₄ → Hg₂SO₄ + 2 HNO₃ It can also be prepared by reacting an excess of mercury with concentrated sulfuric acid: :2 Hg + 2 H₂SO₄ → Hg₂SO₄ + 2 H₂O + SO₂

Use in electrochemical cells

Mercury(I) sulfate is often used in

electrochemical cell An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic o ...

s. It was first introduced in electrochemical cells by Latimer Clark in 1872,"George Augustus Hulett: from Liquid Crystals to Standard Cell" by John T. Stock. ''Bull. Hist. Chem.'' Volume 25, Number 2, 2000, p.91-98 It was then alternatively used in

Weston cell The Weston standard cell is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters. Invented by Edward Weston in 1893, it was adopted as the International Standard for EMF fro ...

s made by George Augustus Hulett in 1911. It has been found to be a good electrode at high temperatures above 100 °C along with silver sulfate. Mercury(I) sulfate has been found to decompose at high temperatures. The decomposition process is

endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...

, 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."Sulphates of Mercury and Standard Cells." by Elliott, R. B. and Hulett, G. A. ''The Journal of Physical Chemistry'' 36.7 (1932): 2083–2086.

References

{{Sulfates Sulfates Mercury(I) compounds