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INORGANIC CHEMISTRY > T4 SULPHUR > Flashcards

T4 SULPHUR Flashcards

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1
Q

Where is elemental S found naturally?

A

Volcanic zones in Indonesia, Chile, and Japan. Also, in deposits in Mexico and the USA formed by anaerobic bacteria action on sulfates.

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2
Q

What are the traditional methods of obtaining sulfur?

A

Sicilian process and Frasch process.

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3
Q

Describe the Sicilian process.

A

Melting the native sulfur and separating it from solid impurities.

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4
Q

Explain the Frasch process.

A

Injecting superheated water to melt sulfur, then injecting hot pressurized air. It’s polluting and mostly discontinued.

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5
Q

How is sulfur primarily obtained nowadays?

A

As a byproduct of oil and natural gas refining in the petrochemical industry, using the Claus process.

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6
Q

What are the allotropic forms of sulfur?

A

S6, S7, S8, S9, S10, S11, S12, S18, S20, and plastic sulfur (S∞).

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7
Q

What are the steps of the Claus process?

A

Partial oxidation of H2S to SO2, then comproportionation reaction between excess H2S and SO2.

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8
Q

Describe the structure of cyclic allotropes of sulfur.

A

Rings with non-planar geometry and S–S bonds.

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9
Q

Which allotropes of sulfur are most stable?

A

S6 (chair), S8 (crown), and S12.

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9
Q

What is notable about the crystalline packing of S8 polymorphs?

A

They have different densities due to different crystal packing.

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10
Q

How many polymorphic forms does S8 have?

A

Two: a rhombic form (a) and a monoclinic form (b).

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11
Q

Which form of S8 is the most stable?

A

The rhombic form (a), found in nature as yellow crystals.

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12
Q

What happens to sulfur at 367 K?

A

Rhombic form transforms reversibly to the monoclinic form.

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13
Q

How does sulfur behave when heated quickly?

A

It melts at 385 K and crystallizes into the monoclinic form if cooled to 373 K.

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14
Q

What distinguishes sulfur from oxygen in terms of chemical properties?

A

Larger size and lower electronegativity of sulfur compared to oxygen.

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14
Q

How does polymorphism affect the properties of sulfur?

A

Crystal packing affects properties such as color, viscosity, and phase transitions.

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15
Q

How does the larger size of sulfur affect its chemistry?

A

Allows for higher coordination numbers and the existence of higher oxidation states.

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16
Q

What is catenation in the chemistry of sulfur?

A

Tendency to form chains due to the weakness of S=S bonds.

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17
Q

What are some common reactions of sulfur?

A

Direct combination with halogens, reaction with metals to form sulfides, and dehydrogenation of hydrocarbons.

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18
Q

What is the reactivity of sulfur?

A

Moderate.

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19
Q

How does S8 react in air?

A

Burns with a blue flame, producing SO2.

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20
Q

Which halogens does S8 react with directly?

A

F2, Cl2, Br2.

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21
Q

Does S8 react directly with I2?

A

no

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22
Q

What happens to saturated hydrocarbons when heated with sulfur?

A

They undergo dehydrogenation.

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23
Q

Which oxidation states can sulfur access?

A

All even states from -2 to +6, and some intermediate ones.

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24
Q

Describe the behavior of sulfur in the +6 oxidation state.

A

Forms weakly oxidizing H2SO4 in acidic conditions.

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25
Q

What happens to sulfate in basic solutions?

A

It exhibits poor oxidation power.

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26
Q

Explain the behavior of sulfur in the +5 oxidation state.

A

Undergoes dismutation at pH = 0 and remains stable in water.

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27
Q

In what conditions is thiosulfate stable?

A

Neutral or alkaline conditions.

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28
Q

What are the most important sulfur oxides?

A

SO2 and SO3.

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29
Q

What is the structure of the SO2 molecule?

A

Angular with two equivalent bonds of order 3/2.

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30
Q

Describe SO2.

A

Colorless, dense, and toxic gas.

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31
Q

What is the main use of SO2?

A

Synthesis of H2SO4.

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32
Q

Explain the preparation of SO2.

A

By combustion of sulfur or roasting metal sulfides.

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33
Q

What is the industrial synthesis method of SO3?

A

Oxidation of SO2 using V2O5 as a catalyst.

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33
Q

What is SO2’s role as a Lewis acid?

A

It’s a suitable solvent for Lewis bases.

34
Q

What is the structure of SO3 in the gaseous phase?

A

Triangular planar with three equivalent double bonds.

35
Q

What are the different types of reactions H2SO4 can undergo?

A

Acidic, oxidizing, dehydrating, sulfonating, and as a base.

35
Q

Describe the properties of sulfuric acid (H2SO4).

A

Dense, viscous liquid that freezes at 10.4 ºC.

36
Q

How is H2SO4 synthesized industrially?

A

Via the Contact method involving combustion of sulfur, catalytic oxidation of SO2, and reaction of SO3 with water.

37
Q

What are the uses of H2SO4?

A

Synthesis of various chemicals, fertilizers, in iron and steel manufacturing, battery electrolyte, drain cleaners, etc.

38
Q

What are sulfites and sulfates?

A

Common anions derived from sulfur oxides.

39
Q

How is Na2SO3 obtained?

A

By bubbling SO2 through a NaOH solution.

40
Q

Describe the structure of SO3 2–.

A

Trigonal pyramid with three equivalent bonds of order 4/3.

41
Q

What are the properties of sulfates?

A

Most are soluble, thermally stable, and do not change the pH of solutions.

42
Q

How can SO4 2– be detected?

A

By forming a white precipitate with Ba2+.

43
Q

How are sulfates prepared?

A

By addition of H2SO4 to a base or oxidation of a metal with H2SO4.

44
Q

What is the role of peroxodisulfuric acid (H2S2O8)?

A

It’s a strongly oxidizing agent containing a peroxide group bonding two sulfate groups.

44
Q

What is the structure of the SO4 2– anion?

A

Tetrahedral with four S–O bonds.

45
Q

Name the four groups of catenated oxo species.

A

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–).

45
Q

What are catenated oxoacids and oxoanions?

A

They possess S–S bonds.

46
Q

Describe the structure of the thiosulfate anion (S2O3 2–).

A

Tetrahedral with one O atom replaced by S, featuring a S–S single bond and three S–O bonds.

47
Q

What is sodium thiosulphate (Na2S2O3) commonly used for?

A

In photographic processing as a fixer for removing AgBr from photographic emulsions.

48
Q

Explain the use of sodium thiosulphate pentahydrate (Na2S2O3.5H2O).

A

It’s an energy storing system that releases heat upon dissolution, commonly known as “hipo”.

49
Q

What are the products of the decomposition of Na2S2O3 upon heating?

A

S compounds in three oxidation states.

50
Q

How is S2O3 2– used in redox titrations?

A

In iodine determination via reduction to I– and oxidation to tetrathionate (S4O6 2–).

51
Q

What is an important application of S2O3 2– in the extraction of gold?

A

Formation of stable [Au(S2O3)2]3– complexes.

52
Q

What percentage of sulfur obtained worldwide is used for producing H2SO4?

A

90%.

53
Q

How is elemental sulfur used in rubber vulcanization?

A

By hydrogenation of alkanes, which crosslinks polyisoprene chains through disulfide bonds.

54
Q

What is the significance of sulfur in biological systems?

A

It’s the 7th most abundant element in humans, present in amino acids like cysteine and methionine.

55
Q

Name some applications of elemental sulfur.

A

Fungicides, fertilizers, creams for skin diseases, manufacture of gunpowder and matches, Na/S batteries, wine preservation, etc.

56
Q

What is the role of disulfide bonds in structural proteins?

A

They confer toughness and rigidity, found in feathers, hair, nails, etc.

57
Q

Which amino acids contain most of the sulfur in humans?

A

Cysteine and methionine.

58
Q

How are disulfide bonds broken in hair during permanent waves?

A

By reducing them to cysteine terminal residues.

59
Q

Name some antibiotics containing sulfur.

A

Penicillin and sulfonamide.

60
Q

What role do thiol groups play in cells?

A

They act as antioxidants, with glutathione being one of the most important.

61
Q

What are iron-sulfur proteins, and what is their significance?

A

They contain iron-sulfur clusters participating in electron transfer processes, crucial for various cellular functions like respiration and nitrogen fixation.

62
Q

What is the role of sulfur in iron-sulfur proteins like ferredoxins?

A

It forms clusters essential for electron transport in photosynthesis and respiration.

63
Q

Name an important iron-sulfur protein involved in nitrogen fixation.

A

Nitrogenase, containing the FeMo cofactor, which converts atmospheric N2 to NH3.

64
Q

How is sulfur metabolized by organisms?

A

Through oxidation and reduction reactions.

65
Q

Name some reduced sulfur compounds.

A

H2S, S, SO3 2–, S2O3 2–, S4O6 2–.

66
Q

What role does sulfur play in the metabolism of some lithotrophic bacteria and archaea?

A

It serves as the sole energy source.

67
Q

Which enzymes are utilized by sulfur oxidizers to oxidize sulfur compounds to sulfate?

A

Sulfide: quinone reductase, sulfur dioxygenase, and sulphite oxidase.

68
Q

How do chemosynthetic archaea use hydrogen sulfide?

A

As an energy source for carbon fixation, producing sugars.

69
Q

In which organisms does sulfur reduction occur?

A

Plants, fungi, and many bacteria, including sulfate-reducing bacteria (SRB).

70
Q

What electron acceptor is used in anaerobic respiration during sulfur reduction?

A

Sulfate.

71
Q

What do sulfate-reducing bacteria reduce sulfate to?

A

Sulfide (H2S).

72
Q

How do plants utilize sulfate?

A

They take up sulfate in their roots and reduce it to sulfide.

73
Q

What is the sulfur cycle?

A

It’s a biogeochemical cycle describing the movement of sulfur between minerals and living organisms.

74
Q

What is assimilative sulfate reduction?

A

Reduction of SO4 2− to thiols by plants, fungi, and various prokaryotes.

75
Q

Describe desulfurization in the sulfur cycle.

A

Organic molecules containing S are desulfurized, producing H2S.

76
Q

What is the product of the oxidation of hydrogen sulfide?

A

Elemental sulfur (S8).

77
Q

Which organisms are involved in the oxidation of elemental sulfur to sulfate?

A

Sulfur oxidizers.

78
Q

What is dissimilative sulfur reduction?

A

Reduction of elemental sulfur to H2S.

79
Q

Describe dissimilative sulfate reduction.

A

Reduction of sulfate to H2S.

80
Q

What role do photosynthetic green and purple sulfur bacteria play in the sulfur cycle?

A

They oxidize hydrogen sulfide to elemental sulfur.

81
Q

How is sulfur involved in the production of thiols?

A

Through assimilative sulfate reduction, where SO4 2− is reduced to thiols.

82
Q

What is the end product of the sulfur cycle?

A

H2S.

83
Q

Why is the sulfur cycle important?

A

It regulates the availability of sulfur for biological processes and contributes to the global sulfur balance.

INORGANIC CHEMISTRY (4 decks)

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