Hydrogen sulfide (H2S, CAS# 7783-06-4) is an extremely hazardous(nguy hiểm), toxic compound(hợp chất. It is a colourless, flammable(dễ cháy) gas that can be identified in relatively low concentrations, by a characteristic rotten egg odor. The gas occurs naturally in coal pits, sulfur springs, gas wells, and as a product of decaying sulfur-containing organic matter, //particularly under low oxygen conditions. It is therefore commonly encountered in places such as sewers, sewage treatment plants (H2S is often called sewer gas), manure stockpiles, mines, hot springs, and the holds of fishing ships. Industrial sources of hydrogen sulfide include petroleum and natural gas extraction and refining, pulp and paper manufacturing, rayon textile production, leather tanning, chemical manufacturing and waste disposal.
Hydrogen sulfide has a very low odor threshold, with its smell being easily perceptible at concentrations well below 1 part per million (ppm) in air. The odor increases as the gas becomes more concentrated, with the strong rotten egg smell recognisable up to 30 ppm. Above this level, the gas is reported to have a sickeningly sweet odor up to around 100 ppm. However, at concentrations above 100 ppm, a person`s ability to detect the gas is affected by rapid temporary paralysis of the olfactory nerves in the nose, leading to a loss of the sense of smell. This means that the gas can be present at dangerously high concentrations, with no perceivable odor. Prolonged exposure to lower concentrations can also result in similar effects of olfactory fatigue. This unusual property of hydrogen sulfide makes it extremely dangerous to rely totally on the sense of smell to warn of the presence of the gas.
Health Effects of Hydrogen Sulfide
H2S is classed as a chemical asphyxiant(chất gây ngạt thở), similar to carbon monoxide and cyanide gases. It inhibits cellular respiration and uptake of oxygen, causing biochemical suffocation. Typical exposure symptoms include:
L O W
0 - 10 ppm
Irritation of the eyes, nose and throat(gây rát , đau mắt, mũi,cổ họng)

M O D
10 - 50 ppm
Headache Dizziness Nausea and vomiting (cảm giác buồn nôn, ói) Coughing and breathing difficulty

H I G H
50 - 200 ppm
Severe respratory tract irritation (tổn th ương đ ường thở) Eye irritation / acute conjunctivitis Shock Convulsions Coma Death in severe cases

Prolonged exposures at lower levels can lead to bronchitis, pneumonia, migraine headaches, pulmonary edema, and loss of motor coordination.

Chapter 8. Microscale Gas Chemistry:
Hydrogen Sulfide Information

A. Appearance     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 of H2S      Hydrogen sulfide has a structure similar to that of water.


This is where the similarity ends, however.  Sulfur is not nearly as electronegative(hoạt động hoá học) 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

C. History      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
H2S(g) <====>  H2S(aq)    
III. Trạng thái tự nhiên và điều chế
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