T4 SULPHUR Flashcards
Where is elemental S found naturally?
Volcanic zones in Indonesia, Chile, and Japan. Also, in deposits in Mexico and the USA formed by anaerobic bacteria action on sulfates.
What are the traditional methods of obtaining sulfur?
Sicilian process and Frasch process.
Describe the Sicilian process.
Melting the native sulfur and separating it from solid impurities.
Explain the Frasch process.
Injecting superheated water to melt sulfur, then injecting hot pressurized air. It’s polluting and mostly discontinued.
How is sulfur primarily obtained nowadays?
As a byproduct of oil and natural gas refining in the petrochemical industry, using the Claus process.
What are the allotropic forms of sulfur?
S6, S7, S8, S9, S10, S11, S12, S18, S20, and plastic sulfur (S∞).
What are the steps of the Claus process?
Partial oxidation of H2S to SO2, then comproportionation reaction between excess H2S and SO2.
Describe the structure of cyclic allotropes of sulfur.
Rings with non-planar geometry and S–S bonds.
Which allotropes of sulfur are most stable?
S6 (chair), S8 (crown), and S12.
What is notable about the crystalline packing of S8 polymorphs?
They have different densities due to different crystal packing.
How many polymorphic forms does S8 have?
Two: a rhombic form (a) and a monoclinic form (b).
Which form of S8 is the most stable?
The rhombic form (a), found in nature as yellow crystals.
What happens to sulfur at 367 K?
Rhombic form transforms reversibly to the monoclinic form.
How does sulfur behave when heated quickly?
It melts at 385 K and crystallizes into the monoclinic form if cooled to 373 K.
What distinguishes sulfur from oxygen in terms of chemical properties?
Larger size and lower electronegativity of sulfur compared to oxygen.
How does polymorphism affect the properties of sulfur?
Crystal packing affects properties such as color, viscosity, and phase transitions.
How does the larger size of sulfur affect its chemistry?
Allows for higher coordination numbers and the existence of higher oxidation states.
What is catenation in the chemistry of sulfur?
Tendency to form chains due to the weakness of S=S bonds.
What are some common reactions of sulfur?
Direct combination with halogens, reaction with metals to form sulfides, and dehydrogenation of hydrocarbons.
What is the reactivity of sulfur?
Moderate.
How does S8 react in air?
Burns with a blue flame, producing SO2.
Which halogens does S8 react with directly?
F2, Cl2, Br2.
Does S8 react directly with I2?
no
What happens to saturated hydrocarbons when heated with sulfur?
They undergo dehydrogenation.
Which oxidation states can sulfur access?
All even states from -2 to +6, and some intermediate ones.
Describe the behavior of sulfur in the +6 oxidation state.
Forms weakly oxidizing H2SO4 in acidic conditions.
What happens to sulfate in basic solutions?
It exhibits poor oxidation power.
Explain the behavior of sulfur in the +5 oxidation state.
Undergoes dismutation at pH = 0 and remains stable in water.
In what conditions is thiosulfate stable?
Neutral or alkaline conditions.
What are the most important sulfur oxides?
SO2 and SO3.
What is the structure of the SO2 molecule?
Angular with two equivalent bonds of order 3/2.
Describe SO2.
Colorless, dense, and toxic gas.
What is the main use of SO2?
Synthesis of H2SO4.
Explain the preparation of SO2.
By combustion of sulfur or roasting metal sulfides.
What is the industrial synthesis method of SO3?
Oxidation of SO2 using V2O5 as a catalyst.
What is SO2’s role as a Lewis acid?
It’s a suitable solvent for Lewis bases.
What is the structure of SO3 in the gaseous phase?
Triangular planar with three equivalent double bonds.
What are the different types of reactions H2SO4 can undergo?
Acidic, oxidizing, dehydrating, sulfonating, and as a base.
Describe the properties of sulfuric acid (H2SO4).
Dense, viscous liquid that freezes at 10.4 ºC.
How is H2SO4 synthesized industrially?
Via the Contact method involving combustion of sulfur, catalytic oxidation of SO2, and reaction of SO3 with water.
What are the uses of H2SO4?
Synthesis of various chemicals, fertilizers, in iron and steel manufacturing, battery electrolyte, drain cleaners, etc.
What are sulfites and sulfates?
Common anions derived from sulfur oxides.
How is Na2SO3 obtained?
By bubbling SO2 through a NaOH solution.
Describe the structure of SO3 2–.
Trigonal pyramid with three equivalent bonds of order 4/3.
What are the properties of sulfates?
Most are soluble, thermally stable, and do not change the pH of solutions.
How can SO4 2– be detected?
By forming a white precipitate with Ba2+.
How are sulfates prepared?
By addition of H2SO4 to a base or oxidation of a metal with H2SO4.
What is the role of peroxodisulfuric acid (H2S2O8)?
It’s a strongly oxidizing agent containing a peroxide group bonding two sulfate groups.
What is the structure of the SO4 2– anion?
Tetrahedral with four S–O bonds.
Name the four groups of catenated oxo species.
Thiosulfuric acid (H2S2O3) and thiosulfate anion (S2O3 2–), dithionous acid (H2S2O4) and dithionite (S2O4 2–), dithionic acid (H2S2O6) and dithionate (S2O6 2–), and polythionic acids (H2S2+NO6) and polythionates (SN+2O6 2–).
What are catenated oxoacids and oxoanions?
They possess S–S bonds.
Describe the structure of the thiosulfate anion (S2O3 2–).
Tetrahedral with one O atom replaced by S, featuring a S–S single bond and three S–O bonds.
What is sodium thiosulphate (Na2S2O3) commonly used for?
In photographic processing as a fixer for removing AgBr from photographic emulsions.
Explain the use of sodium thiosulphate pentahydrate (Na2S2O3.5H2O).
It’s an energy storing system that releases heat upon dissolution, commonly known as “hipo”.
What are the products of the decomposition of Na2S2O3 upon heating?
S compounds in three oxidation states.
How is S2O3 2– used in redox titrations?
In iodine determination via reduction to I– and oxidation to tetrathionate (S4O6 2–).
What is an important application of S2O3 2– in the extraction of gold?
Formation of stable [Au(S2O3)2]3– complexes.
What percentage of sulfur obtained worldwide is used for producing H2SO4?
90%.
How is elemental sulfur used in rubber vulcanization?
By hydrogenation of alkanes, which crosslinks polyisoprene chains through disulfide bonds.
What is the significance of sulfur in biological systems?
It’s the 7th most abundant element in humans, present in amino acids like cysteine and methionine.
Name some applications of elemental sulfur.
Fungicides, fertilizers, creams for skin diseases, manufacture of gunpowder and matches, Na/S batteries, wine preservation, etc.
What is the role of disulfide bonds in structural proteins?
They confer toughness and rigidity, found in feathers, hair, nails, etc.
Which amino acids contain most of the sulfur in humans?
Cysteine and methionine.
How are disulfide bonds broken in hair during permanent waves?
By reducing them to cysteine terminal residues.
Name some antibiotics containing sulfur.
Penicillin and sulfonamide.
What role do thiol groups play in cells?
They act as antioxidants, with glutathione being one of the most important.
What are iron-sulfur proteins, and what is their significance?
They contain iron-sulfur clusters participating in electron transfer processes, crucial for various cellular functions like respiration and nitrogen fixation.
What is the role of sulfur in iron-sulfur proteins like ferredoxins?
It forms clusters essential for electron transport in photosynthesis and respiration.
Name an important iron-sulfur protein involved in nitrogen fixation.
Nitrogenase, containing the FeMo cofactor, which converts atmospheric N2 to NH3.
How is sulfur metabolized by organisms?
Through oxidation and reduction reactions.
Name some reduced sulfur compounds.
H2S, S, SO3 2–, S2O3 2–, S4O6 2–.
What role does sulfur play in the metabolism of some lithotrophic bacteria and archaea?
It serves as the sole energy source.
Which enzymes are utilized by sulfur oxidizers to oxidize sulfur compounds to sulfate?
Sulfide: quinone reductase, sulfur dioxygenase, and sulphite oxidase.
How do chemosynthetic archaea use hydrogen sulfide?
As an energy source for carbon fixation, producing sugars.
In which organisms does sulfur reduction occur?
Plants, fungi, and many bacteria, including sulfate-reducing bacteria (SRB).
What electron acceptor is used in anaerobic respiration during sulfur reduction?
Sulfate.
What do sulfate-reducing bacteria reduce sulfate to?
Sulfide (H2S).
How do plants utilize sulfate?
They take up sulfate in their roots and reduce it to sulfide.
What is the sulfur cycle?
It’s a biogeochemical cycle describing the movement of sulfur between minerals and living organisms.
What is assimilative sulfate reduction?
Reduction of SO4 2− to thiols by plants, fungi, and various prokaryotes.
Describe desulfurization in the sulfur cycle.
Organic molecules containing S are desulfurized, producing H2S.
What is the product of the oxidation of hydrogen sulfide?
Elemental sulfur (S8).
Which organisms are involved in the oxidation of elemental sulfur to sulfate?
Sulfur oxidizers.
What is dissimilative sulfur reduction?
Reduction of elemental sulfur to H2S.
Describe dissimilative sulfate reduction.
Reduction of sulfate to H2S.
What role do photosynthetic green and purple sulfur bacteria play in the sulfur cycle?
They oxidize hydrogen sulfide to elemental sulfur.
How is sulfur involved in the production of thiols?
Through assimilative sulfate reduction, where SO4 2− is reduced to thiols.
What is the end product of the sulfur cycle?
H2S.
Why is the sulfur cycle important?
It regulates the availability of sulfur for biological processes and contributes to the global sulfur balance.
