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Hydrogen peroxide readily decomposes on heating and in the presence of various catalysts.
2H2 O2 (aq) → 2H 2 O(l) + O 2 (g)
This is a disproportionation reaction in which one O atom in H2 O2 is reduced and the other one is oxidized. Sulfur. Although it is not very abundant, sulfur is readily available because of its occurrence in large
deposits of the free element. Sulfur is extracted from these underground deposits by the Frasch process. There are
several allotropic forms of sulfur. The most important are rhombic sulfur and monoclinic sulfur. Rhombic
sulfur is the more stable form at room temperature. In this form, sulfur atoms are linked to each other as
puckered, eight-membered rings, S8 . Above 96°C, monoclinic sulfur is more stable. This form melts at 119°C.
Above 150°C, the pale yellow liquid becomes more viscous as the rings break open and the newly formed
molecular chains entangle. Sulfur has a wide range of oxidation numbers in its compounds, as shown in Table
21.3 of the text. The major end uses of sulfur are in fertilizers (60%) and in chemicals (20%).
Hydrogen Sulfide. H 2 S (oxidation number –2) is a colorless, highly toxic gas, with an offensive odor.
When dissolved in water the resulting solution is called hydrosulfuric acid. H2 S(aq) is a weak acid. In the
laboratory, H2 S(aq) is used to separate groups of metal ions for their qualitative analysis. It is often prepared in
the laboratory by the hydrolysis of thioacetamide.
+ CH3 CSNH 2 (aq) + 2H2 O + H +(aq) → CH 3 COOH(aq) + NH4 (aq) + H2 S(aq) Oxides of Sulfur. The major oxides of sulfur are sulfur dioxide and sulfur trioxide, SO2 and SO3 . Sulfur
dioxide is a colorless gas with a pungent odor and is quite toxic. It dissolves in water forming sulfurous acid.
SO2 (g) + H 2 O(l) → H2 SO3 (aq)
Sulfur dioxide is slowly oxidized in air to sulfur trioxide.
2SO2 (g) + O 2 (g) → 2SO 3 (g)
Sulfur trioxide dissolves in water to form sulfuric acid.
SO3 (g) + H 2 O(l) → H2 SO4 (aq)
Sulfur dioxide is a major air pollutant. It is formed during combustion of sulfur-containing oil and coal.
Smelters and coal-fired electric power plants are the primary sources of sulfur oxides. Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website 4 24 / Nonmetallic Elements and Their Compounds
Sulfuric Acid. More sulfuric acid is produced each year than any other industrial chemical. It is
formed from SO3 and H2 O as shown above. First, sulfur is burned in air to make SO2 . Second, a vanadium
oxide catalyst is used to convert SO2 to SO3 in the presence of oxygen. Third, SO 3 and water react as above.
Hot, concentrated sulfuric acid is a strong oxidizing agent. In such a solution, the oxidizing agent is
actually the sulfate ion. Copper is oxidized by sulfuric acid by the following reaction:
Cu(s) + 2H 2 SO4 (aq) → CuSO4 (aq) + SO2 (g) + 2H 2 O(l)
EXAMPLE 21.5 Oxygen Compounds
Distinguish between the three types...
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