Chapter 8. Microscale Gas Chemistry:
Hydrogen sulfide is a colorless gas with an offensive stench and is said to smell like rotten eggs. The gas can be detected at a level of 2 parts per billion. To put this into perspective, 1 mL of the gas distributed evenly in a 100-seat lecture hall is about 20 ppb.
B. Physical Properties
Hydrogen sulfide has a structure similar to that of water.
This is where the similarity ends, however. Sulfur is not nearly as electronegative as oxygen so that hydrogen sulfide is not nearly as polar as water. Because of this, comparatively weak intermolecular forces exist for H2S and the melting and boiling points are much lower than they are in water. Hydrogen sulfide and water boil at -60.7 oC and +100.0 oC , respectively.
Hydrogen Sulfide, H2S Atomic mass: 34.08 g/mol melting point -85.5 oC boiling point -60.7 oC
Hydrogen sulfide has been known since early times. The chemistry of H2S has been studied since the 1600s. In the 19th century, Petrus Johannes Kipp, a Dutch pharmacist invented a convenient device for the generation of a variety of gases in which a liquid and solid were the reagents. The ‘Kipp generator’ was especially useful for the generation of hydrogen sulfide and hydrogen. The device shown at right was one of the earliest and would not be familiar to chemists who remember using the Kipp generator in chemistry lab. More information on the use of this device is given in the history portion of our gas chemistry web site.
D. Natural Abundance
Natural gas contains up to several percent H2S(g) and as such are called sour gas wells from their offensive stench. Volcanoes also discharge hydrogen sulfide. Anaerobic decay aided by bacteria produces hydrogen sulfide, which in turn, produces sulfur. This process accounts for much of the native sulfur found in nature.
E. Industrial Production
Commercially hydrogen sulfide is obtained from "sour gas" natural gas wells.
F. Industrial Uses
Hydrogen sulfide has few important commercial uses. However, it is used to produce sulfur which is one of the most commercially important elements. About 25% of all sulfur is obtained from natural gas and crude oil by conversion of 1/3 of the H2S to SO2 and then followed by the reaction between H2S and SO2:
2 H2S(g) + 3 O2(g) ---> 2 SO2(g) + 2 H2O(g)
16 H2S(g) + 8 SO2(g) ---> 3 S8(g) + 16 H2O(g)
Hydrogen sulfide has
been used for well over a century as a method of qualitative analysis of
metal ions. In fact, the Chemistry Building at the University of
Illinois in 1915 had a built-in supply of hydrogen sulfide to the various
labs, i.e., H2S 'on tap'! The gas was stored
in a 500-gallon tank! (Chemical Discovery and Invention in
the Twentieth Century, Sir William Tildon, 1917)
G. Gas Density of H2S
The density of hydrogen sulfide is 1.393 g/L at 25 oC and 1 atm. This is 18% greater than that of air.
H. Gas Solubility of H2S
Hydrogen sulfide dissolves in water to make a solution that is weakly acidic. At 0 oC 437 mL H2S(g) will dissolve in 100 mL H2O, producing a solution that is about 0.2 M. However, the solution process is fairly slow. The solution equilibrium is
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