Mercury(I) sulfate


Mercury sulfate, commonly called mercurous sulphate or mercurous sulfate is the chemical compound Hg2SO4. Mercury 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. It is highly toxic; it could be fatal if inhaled, ingested, or absorbed by skin.

Structure

The crystal structure of mercurous sulfate is made up of Hg22+ dumbbells and SO42− anions as main building units. Hg22+ dumbbell is surrounded by four oxygen atoms, with the Hg₋O distance ranging from 2.23 to 2.93 Å, whereas the Hg-Hg distance is about 2.50 Å.
Studies have shown mercury sulfate to have the mercury atoms arranged in doublets with a bond distance of 2.500 Å. The metal atom doublets are oriented parallel to the an axis in a unit cell. Mercury doublets form part of an infinite chain: SO4 - Hg - Hg - SO4 - Hg - Hg - … The Hg - Hg - O bond angle is 165°±1°. The chain crosses the unit cell diagonally. The mercury sulfate structure is held together by weak Hg-O interactions. The SO4 does not act as a single anion, but rather is coordinated to the mercury metal.

Preparation

One way to prepare mercury sulfate is to mix the acidic solution of mercury nitrate with 1 to 6 sulfuric acid solution:,
It can also be prepared by reacting an excess of mercury with concentrated sulfuric acid:

Use in electrochemical cells

Mercury sulfate is often used in electrochemical cells. It was first introduced in electrochemical cells by Latimer Clark in 1872, It was then alternatively used in Weston cells 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 sulfate has been found to decompose at high temperatures. The decomposition process is endothermic and occurs between 335°C and 500°C.
Mercury sulfate has unique properties that make the standard cells possible. It has a rather low solubility ; diffusion from the cathode system is not excessive; and it is sufficient to give a large potential at a mercury electrode.