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Why can't I find information about certain mercurous compounds in any texts?
- What does mercurous carbonate look like and why can't I find in chemistry books?
Ciske
1/19/99
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The mercury(I) ion, Hg22+, is an unusual ion of a very peculiar metal. Most mercury(I) compounds are unstable, especially when exposed to water or light, or when heated. Because they are rather uncommon
they are mentioned only in passing in most introductory texts.
Mercury (I) (or mercurous) compounds decompose on exposure to water into liquid mercury and mercury(II) (or mercuric) compounds. The equilibrium constant for the disproportionation of mercury(I) ion
Hg22+(aq) = Hg( ) + Hg2+(aq)
is 6.0×10-3. So while the equilibrium normally lies to the left, the balance is rather delicate.
Addition of any anion that precipitates or complexes Hg2+ more than Hg22+ shifts the equilibrium to the right.
The result is disproportionation rather than formation of a mercury(I) compound. For example, mercury(I) sulfide
decomposes in the presence of water because mercury(II) sulfide (cinnabar) is almost completely insoluble:
Hg22+(aq) + S2-(aq) Hg( ) + HgS(s)
A partial list of mercurous compounds, taken from the Merck Index and the CRC Handbook of chemistry and physics.
Name |
Formula |
Appearance |
Decomposes on exposure to: |
mercury(I) acetate |
Hg2(C2H3O2)2 |
flat sheetlike crystals |
light, water |
mercury(I) azide |
Hg2(N3)2 |
white crystals |
shock, light, heat (explosive!) |
mercury(I) bromate |
Hg2(BrO3)2 |
crystals |
water, heat |
mercury(I) bromide |
Hg2Br2 |
white tetrahedral crystals |
light |
mercury(I) carbonate |
Hg2CO3 |
yellow-brown crystals |
light, heat, water |
mercury(I) chloride (calomel) |
Hg2Cl2 |
white tetrahedral crystals |
light |
mercury(I) chlorate |
Hg2(ClO3)2 |
white crystals |
light |
mercury(I) chromate |
Hg2CrO4 |
red needles or powder |
heat |
mercury(I) fluoride |
Hg2F2 |
yellow cubic crystals |
light, heat (as liquid), water |
mercury(I) formate |
Hg2(CHO2)2 |
shiny scales |
heat, hot water |
mercury(I) iodate |
Hg2(IO3)2 |
yellow powder |
heat (at 250°C) |
mercury(I) iodide |
Hg2I2 |
yellow tetrahedral crystals |
light, heat (at 290°C) |
mercury(I) nitrate |
Hg2(NO3)2·2H2O |
monoclinic crystals |
light, water |
mercury(I) nitrite |
Hg2(NO2)2 |
yellow |
heat (at 100°C), water |
mercury(I) oxide |
Hg2O |
black or brown-black powder |
light, heat (at 100°C) |
mercury(I) sulfate |
Hg2SO4 |
white-yellow powder |
light, heat, water |
mercury(I) sulfide |
Hg2S |
black solid |
heat, water |
References
- F. A. Cotton and G. Wilkinson in Advanced Inorganic Chemistry, Wiley Interscience, New York, 1988.
- The Merck Index, 8th ed., Merck & Co., 1968.
- The CRC Handbook of Chemistry and Physics, 78th ed., eds. D. L. Lide and H.P.R. Frederikse, CRC Press, 1998
Resources
Mercury (J. P. Birk, Arizona State University)
Author: Fred Senese senese@antoine.frostburg.edu
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