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Basic Knowledge of Inorganic Chemistry 14: “Chemical Properties of Hydrogen Sulfide”. Flammability: Completely dry hydrogen sulfide does not react with oxygen in the air at room temperature, but it can burn when ignited; it burns during drilling operations or when there is a leak underground, with a combustion rate of around 86%. When hydrogen sulfide burns, it produces a blue flame and toxic sulfur dioxide gas, which can damage human eyes and lungs. When there is an adequate supply of air, SO2 and H2O are produced. http://e.hiphotos.baidu.com/baike/s%3D199/sign=9794d006cdfc1e17f9bf88387390f67c/63d9f2d3572c11df7dd1d833612762d0f703c29a.jpg When there is insufficient air or the temperature is low, free S and H2O are produced. http://g.hiphotos.baidu.com/baike/s%3D160/sign=4ff26b32b11bb0518b24b72e067bda77/42166d224f4a20a4a0a65bd792529822720ed062.jpg Hydrogen sulfide can burn not only in oxygen or air, but also in chlorine and fluorine. Solubility: Soluble hydrogen sulfide gas can dissolve in water, ethanol, and glycerin; it has unstable chemical properties. Hydrogen sulfide is slightly soluble in water, forming a weak acid known as \"hydrogen sulfurous acid\". Its aqueous solution contains hydrogen sulfide ion HS (in a solution at 18 degrees Celsius with a concentration of 0.01–0.1 mol/L, pKa = 6.9) and elemental sulfur ion S (pKa = 11.96). Initially, clear hydrosulfuric acid becomes cloudy after being left for some time, as it undergoes a slow reaction with the oxygen dissolved in water, producing elemental sulfur that is insoluble in water. Hydrogen sulfide is a dibasic weak acid. At 20°C, 1 volume of water can dissolve 2.6 volumes of hydrogen sulfide; the resulting aqueous solution is called hydrosulfuric acid, with a concentration of 0.1 mol/L. The degree of second dissociation of hydrogen sulfide in water is quite low; as a result, the alkalinity of an aqueous solution of sodium sulfide is only slightly lower than that of a sodium hydroxide solution of the same concentration, allowing it to be used as a strong base: http://d.hiphotos.baidu.com/baike/s%3D216/sign=8f30ad3bd01b0ef468e89f5febc551a1/0b55b319ebc4b745685b5203cdfc1e178b8215d3.jpg Hydrogen sulfide exists in solution in accordance with the following equilibrium: http://h.hiphotos.baidu.com/baike/s%3D232/sign=bfb93646533d26972ad30f5e67fab24f/3bf33a87e950352ad9092e845143fbf2b3118bd5.jpg http://h.hiphotos.baidu.com/baike/s%3D236/sign=db360a145cdf8db1b82e7b673f22dddb/bba1cd11728b47103e44f640c1cec3fdfd0323d6.jpg Hydrosulfuric acid has a stronger reducing property than gaseous hydrogen sulfide; it can be easily oxidized by air, resulting in the release of sulfur and making the solution cloudy. In acidic solutions, hydrogen sulfide can reduce Fe3+ to Fe2+, Br2 to Br–, I2 to I–; it can also reduce Mn2+ to Mn+, and Cr3+ to Cr2+. HNO3 is reduced to NO2, while hydrogen sulfide itself is usually oxidized to elemental sulfur. H2S can also reduce copper ions (Cu2+), hyposelenic acid (H2SeO3), and polonium ions in the +4 state (Po4+), among others. For example: http://g.hiphotos.baidu.com/baike/s%3D227/sign=869ffabe013b5bb5bad727fc01d2d523/00e93901213fb80ed5479ac234d12f2eb9389415.jpg Hydrogen sulfide gas can form precipitates with metals, and this property is utilized to remove it. In standard laboratories, hydrogen sulfide is removed by passing it through a copper sulfate solution, resulting in the formation of copper sulfide, which is insoluble in ordinary strong acids (non-oxidizing acids): http://h.hiphotos.baidu.com/baike/s%3D220/sign=ef8e11ebc1fdfc03e178e4bae43e87a9/aec379310a55b319ccb6656041a98226cffc1753.jpg However, when hydrogen sulfide reacts with ferric sulfate, if the amount of hydrogen sulfide is low, only elemental sulfur is produced, as Fe3+ and S2– undergo a redox reaction: http://a.hiphotos.baidu.com/baike/s%3D296/sign=46ec59f1b11c8701d2b6b5ef117e9e6e/4e4a20a4462309f7f8cd4a07700e0cf3d7cad601.jpg Note: The sulfur atom in hydrogen sulfide has a valence of –2, which is its lowest possible valence. But hydrogen has a valence of +1 and can be reduced to a valence of 0; therefore it still possesses oxidizing properties. For example: http://e.hiphotos.baidu.com/baike/s%3D179/sign=7324b37c272dd42a5b0905ac3a3b5b2f/adaf2edda3cc7cd9291ed2cc3b01213fb80e91f0.jpg Hydrogen sulfide can undergo a reduction reaction: http://g.hiphotos.baidu.com/baike/s%3D189/sign=5d00cef669600c33f479dac0234d5134/ac345982b2b7d0a23a97097fc9ef76094a369af1.jpg In this reaction, hydrogen sulfide acts as a reducing agent, sulfur dioxide acts as an oxidizing agent, and sulfur is the oxidation product.