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Sulphur – Introduction, Occurrence, Physical and Chemical Properties, Allotropes, Compounds & Uses of Sulphur

Sulphur – Introduction, Occurrence, Physical and Chemical Properties, Allotropes, Compounds & Uses of Sulphur

Have you ever tried helping your Dad or Mom, prepare a delectable dish? Maybe just by chopping some fresh onions? Or by peeling off and grinding garlic in a mortar and pestle (or in a simpler electric mixer grinder)?

If not, I think you should try some. Why? Because, it is important for a chemistry enthusiast to meet some of the naturally occurring chemical elements present around us, consciously. At least once in a while. So when you cut open an onion, you would probably know how much tears your parents shed every day, preparing the meal you take. And if you stay away from onion and garlic being a Satvik, you must have definitely had an Indian dal or Sambar, tempered with curry leaves and asafoetida (Heeng).

Now, what do you think about the strong characteristic smell of asafoetida? Or even garlic for that matter. What, if I told you that it's all because of the inherent sulphur content present in these food items, that gives them their characteristic smell?

And what about onions making you cry?! Well, that too is due to the liberation of an extremely volatile enzyme called allicin (a sulphur-based compound, a thiosulfinate) which induces tears in our lacrimal glands.

Stranger than this! Did you know that methyl mercaptan is added to natural gas (LPG) we use at home, such that it develops a characteristic odour, so as to intimidate people if at all there is a gas leakage in kitchens or anywhere as such. This chemical too contains sulphur. Let us try to understand more about this interesting element!!

TABLE OF CONTENTS

  • Sulphur- Introduction & Key facts
  • Sulphur - Isotopes & Natural Occurrence
  • Allotropes of Sulphur
  • Physical Properties of Sulphur
  • Chemical Properties of Sulphur
  • Important Compounds of Sulphur
  • Applications of Sulphur
  • Practice Problems
  • Frequently Asked Questions - FAQs

Sulphur – Introduction & Key Facts

Sulphur is a chemical element with the atomic number 16 and the symbol S. It is present in abundance on earth and is multivalent and non-metallic in nature. Sulphur atoms normally combine to create cyclic octatomic molecules, which have the chemical formula S8. At room temperature, elemental sulphur is a crystalline solid that is brilliant yellow in colour.

In terms of mass, sulphur is the tenth most prevalent element in the universe and the fifth most prevalent on Earth.

While pure, native sulphur can occasionally be discovered, it is most frequently found on Earth as the minerals like sulphide and sulphate. Galena (PbS) and Zinc Blende (ZnS), Copper Glance (Cu2S), Iron Pyrite (FeS2), Cinnabar (HgS) and Argentite (Ag2S) also known as Silver Glance are a few examples of Sulphide ores.

  • All life requires sulphur, yet it nearly invariably takes the form of metal sulphides of organosulfur compounds.
  • Organosulfur substances such as amino acids, two vitamins (biotin and thiamine), and two proteinogenic amino acids (cysteine and methionine) are essential for life.
  • Several biological cofactors (influencing physiological functions in our body), such as protein cofactors, such as glutathione and iron-sulphur proteins, also include the elemental sulphur. For example, Proteins with Fe-S clusters are necessary cofactors for a variety of biological functions.
  • The protein keratin, which is present in the outer skin, hair, and feathers, among other things, is strengthened mechanically and rendered insoluble by disulfides and S-S bonds.
  • Sulphur is an essential macronutrient for all living things and one of the fundamental chemical components required for metabolic activity.
  • Prehistoric humans used to utilise sulphur for wall painting as well as a tonic in medication.

Sulphur – Isotopes & Natural Occurrence

There are 23 known isotopes of sulphur. Four among all of these are stable. Their abundance is mentioned herein:

32S (94.99%±0.26%),33S (0.75%±0.02%),34S(4.25%±0.24%),and 36S (0.01%±0.01%)

The radioactive isotopes of sulphur have half-lives of less than 3 hours, with the exception of 35S, which has a half-life of 87 days and was created during the cosmic ray spallation of 40Ar.

By mass, sulphur is the seventh most prevalent element on Earth. In various places across the world, particularly in the Pacific Ring of Fire. The elemental sulphur may be found next to hot springs and volcanic zones; these volcanic resources are now mined in Indonesia, Chile, and Japan.

  • Sulphides or sulphates, which are compounds of sulphur, are present in many significant metal ores. Galena (lead sulphide, PbS), blende (zinc sulphide, ZnS), pyrite (iron disulfide, FeS2), chalcopyrite (copper iron sulphide, CuFeS2), gypsum (calcium sulphate dihydrate, CaSO4.2H2O), and barite are a few significant examples (barium sulphate, BaSO4).
  • Although a method for producing sulfuric acid was invented in the 18th century that used sulphur dioxide produced by burning pyrite, the sulphide ores are mostly prized for their metal content.
  • Compounds containing sulphur can be found in coal, oil, and natural gas.
  • The biggest single crystal recorded in the volcanic deposits of Indonesia, Chile and Japan, which is polycrystalline, measures 221611 cm.
  • Sulphur is an element that naturally exists in volcanic emissions on Earth, including hydrothermal vent emissions.
  • Petroleum and natural gas are currently the primary sources of sulphur for industrial use.

Allotropes of Sulphur

Sulphur has more allotropic forms than any other element. This discrepancy results in part from how much sulphur has polymerized and in part from the crystal shape chosen.

  • Two common forms are 𝛼 or rhombic sulphur and 𝛽 or monoclinic sulphur, which ​, are stable above 95.5 °C​ (transition temperature). These two forms change reversibly with slow​ heating or slow cooling.
  • The third form of sulphur is known as ​, 𝛾-monoclinic. All three forms contain puckered​, S8 rings with a ​crown conformation.​

Rhombic, 𝛼-Sulphur: It is yellow in colour and its specific gravity is 2.06. The melting point is385.8 K . It is readily soluble in CS2. Rhombic sulphur crystals are formed by evaporating the solution of roll sulphur (this is basically obtained as rods or sticks of sulphur which is made by casting molten sulphur in specific moulds) in CS2. It is insoluble in water but gets dissolved to some extent in benzene, alcohol and ether.​

Monoclinic, 𝛽-Sulphur: Its melting point is 393 K​, and specific gravity is 1.98. It is soluble in CS2. This form of sulphur is prepared by melting rhombic sulphur in a dish and cooling it till crust is formed. Two holes are made in the crust and the remaining liquid is poured out. On removing the crust, colourless, needle-shaped​, crystals of 𝛽-sulphur are formed.​

Both rhombic and monoclinic sulphur have S8 molecules, which are packed to give different crystal structures. The S8 ring in both forms is puckered and ​, has a crown shape. Several other modifications​, of sulphur containing​, ring have been synthesised​, in the last two decades. In cyclo-S6, the ring adopts the chair form., 6─20 sulphur atoms per​ ring.

Physical Properties of Sulphur

  • Numerous polyatomic compounds are created by sulphur. The allotrope of sulphur known as cyclo-S8 is octasulfur. Cyclo- S8 has a 0 D dipole moment and has a molecular symmetry that corresponds to a D4d point group. (Point groups are generally symmetry operations that are used to characterize the three-dimensional lattice of a crystal. There are generally 32 sets of such symmetry).
  • Octasulfur is an odourless, soft, bright-yellow solid; nevertheless, impure samples have a distinctive and pungent odour which is at times similar to burnt matchsticks. It sublimates quickly, melts at 115.21 °C (239.38 °F), and boils at 444.6 °C (832.3 °F).
  • Below its melting point, at 95.2 °C (203.4 °F), cyclo-octasulfur (the -polymorph) transforms into the -polymorph.
  • The intermolecular connections are altered by this phase transition, but the structure of the S8 ring remains essentially constant.
  • Octasulfur undergoes a second allotrope transition between its melting and boiling temperatures, switching from β-octasulfur to γ-sulphur, again accompanied by a decreased density but greater viscosity because of the creation of a stabler polymorph.
  • The viscosity reduces when depolymerization takes place at higher temperatures. Above200 °C (392 °F), molten or liquid sulphur appears blood red in colour. Depending on the allotropes, sulphur has a density of around 2.07 g/cm3. All of the stable allotropes are excellent electrical insulators.
  • Unlike other non-polar organic solvents like benzene and toluene, sulphur is soluble in carbon disulfide but insoluble in water.

Chemical Properties of Sulphur

  • In the oxidation states of +2, +4, and +6, respectively, sulphur can form sulphide (S2-), sulfite (SO32-),, and sulphate (SO42-) compounds.
  • It blends with almost all other components. Because sulphur exhibits catenation i.e., the bonding of one identical atom to another, second only to carbon.
  • Hydrogen sulphide and sulfuric acid are the major products of sulphur hydrolysis under normal circumstances:

12 S8 + 4H2O → 3H2S + H2SO4

  • Sulphur interacts with particularly active compounds under normal circumstances (fluorine).

S + 4F2 SF6

  • Heat must be introduced initially or continuously for reactions involving non-metals with oxidative characteristics with respect to sulphur (apart from fluorine) and the majority of metals.

  • Sulphur produces sulphur dioxide (SO2), which has an oppressive and repulsive stench, when it burns in the air with a blue flame.

S + O2 SO2

  • At steady heating, sulphur interacts with hot and concentrated strong acids and melting alkalies.

S +2H2SO4 3SO2 +2H2O

S +6HNO3H2SO4+ 6NO2 +2H2O

6NaOH + 4S → 3H2O + Na2S2O3 +2Na2S

  • Sulphur dioxide (oxidation state +4) is produced when sulphur reacts with oxygen under normal circumstances, whereas sulphur trioxide (oxidation state +6) needs higher temperatures and the presence of a catalyst.

S + O2 SO2(oxidation state of S is +4)

2S + 3O2 2SO3 (oxidation state of S is +6). This reaction occurs at elevated temperatures

  • Nitrides, oxides, fluorides, chlorides, and bromides are some of the compounds sulphur may form, along with sulphur iodide (oxidation state of sulphur in all such compounds is +2).

S + Cl2 SCl2

4S + 2N2 S4N4

  • Sulphur enters a process as an oxidant and produces sulphides with an oxidation state of -2 when it interacts with elements whose electronegativity is less than that of sulphur.

H2+S H2S

  • With the exception of the noble gases, sulphur interacts with almost all other elements, even the infamously inert metal iridium (yielding iridium disulfide, IrS2).

Ir +2S IrS2

Compounds of Sulphur (S)

  • In a highly acidic solution, sulphur reacts with moderate oxidising agents to form the sulphur polycations S82+, S42+, and S162+.
  • Both hydrogen sulphide (H2s) gas and the hydrosulphide anion are particularly poisonous to animals because they prevent haemoglobin and certain cytochromes from transporting oxygen in a way that is similar to cyanide and azide.
  • Many organo-sulphur compounds form major drug or biologically important components. For e.g. penicillin, Allicin.
  • Methionine is a thioether (-S-CH3) that consists of an amino acid group.
  • Sulphonic acids are used as detergents.
  • Polysulfides, which are made up of chains of sulphur atoms ending with S centres, are produced during the reduction of elemental sulphur.

2Na + S8 → Na2S8

  • The sulphur-rich oxides include sulphur monoxide, disulfur monoxide, sulphur dioxides, and higher oxides containing peroxo groups. There are many different sulphur oxides known.

S + O2 → SO2(sulphur dioxide)

2SO2+ O2 → 2SO3 (sulphur trioxide)

SOCl2 + Ag2S → 2AgCl + S2O (disulphur monoxide)

Some oxyanions of sulphur contain peroxy linkages too, like in SO52-, S2O82-. They produce oxoacids of sulphur such as H2SO5 and H2S2O8 that contain peroxy linkages.

  • The compound tetrasulfur tetranitride which has a cage like structure is a significant S-N compound (S4N4). Although it doesn't contain any metal atoms, heating this molecule produces polymeric sulphur nitride (SNx), which has metallic characteristics. The SCN- group is present in thiocyanates.
  • Sulphides are the primary ore types for copper, zinc, nickel, cobalt, molybdenum, and other metals.
  • Sulphur-sulphur bonds serve as structural support for rubber.

Applications of Sulphur

  • Because sulphur is employed in so many industrial processes, it is frequently viewed as a trustworthy indication of business activity and the health of the country's economy.
  • Six-sevenths of all sulphur generated is turned into sulfuric acid, with fertiliser production being its single-largest usage (phosphates and ammonium sulphate).
  • Every year, sulphur is removed from oil and gas refineries and marketed all over the world in quantities of close to 60 million tonnes.
  • Sulphate is mostly produced from the environment in most forest ecosystems, with some sulphur also coming through the weathering of ore minerals and evaporites.
  • Enhanced sulphur has been employed as a tracer in hydrologic research and has been used to detect pollution sources thanks to its specific isotopic makeup.
  • Numerous additional uses are also well-known, such as the manufacture of pigments, detergents, fibres, petroleum products, sheet metal, explosives, storage batteries and tyres.
  • Insecticides, fungicides, dyes, and many more items are made from sulphur that has not been transformed into sulfuric acid.

Practice Problems

Q.1. The oxidation state of sulphur in SO3 molecule is:

  1. +3
  2. +6
  3. +4
  4. -6

Answer: (B)

Let the oxidation state of S be 'x'.

So, x+3(-2)=0

⇒ x=+6

Q.2. Mention some major uses of sulphur?

Answer: Sulphur is employed in the production of fertiliser, water treatment, mineral extraction, oil refining, and automobile batteries. Other uses for compounds based on sulphur include vulcanisation of rubber, bleaching paper, and producing goods like cement, detergents, and insecticides. additional gunpowder.

Q.3. The bond angle between S-S-S in S6 and S8 molecules is the same. True or False?.

Answer: The statement is false. The chair-shaped hexagonal ring in the S6 molecule has the same bond lengths as that in the S8 molecule, but slightly smaller bond angles, meaning that the bond lengths are the same but the bond angles are different.

Q.4. What is the oxidation state of S in S8?

  1. +6
  2. +4
  3. +2
  4. 0

Answer: (D)

Solution: Sulphur is in elemental state in S8. All its allotropic forms has the molecular formula S8 where it attains a puckered ring structure with crown conformation. Hence, it is in zero oxidation state in S8.

So the correct answer is option D.

Frequently Asked Questions-FAQs

Q1. How is sulphur commercially produced?
Answer:
Today, hydrogen sulphide is the major form of sulphur that is created from petroleum, natural gas, and other associated fossil resources. Organosulfur compounds, which are unwanted petroleum contaminants, can be improved by being subjected to hydrodesulfurization, which breaks the C-S bonds.

R-S-R + 2H2 → 2RH + H2S

The Claus process turns the hydrogen sulphide produced as a result of this action, as well as the form it takes in natural gas, into elemental sulphur. In this process, some hydrogen sulphide is converted to sulphur dioxide, and the two are then combined.

3O2 + 2H2S → 2SO2 + 2H2O

SO2+ 2H2S → 3S + 2H2O

Q.2. How beneficial is sulphur for skin?
Answer:
It is generally present in liquid soaps or detergents or body wash products. Sulphur helps absorb excess oil (sebum), which can cause acne outbreaks, and dries up the skin's surface. Additionally, it dries up dead skin cells to aid in pore clearing. Some products include sulphur in addition to resorcinol and other chemicals that are used to treat acne.

Q.3. What are the naturally occurring sources of sulphur?
Answer:
In the human body, sulphur is the third-most prevalent chemical. The ingredient may also be found in a number of meals, such as eggs, garlic, onions, and foods strong in proteins. Cysteine and methionine, are two important amino acids among some more that can only be produced by sulphur.

Q.4. What are the negative impacts of sulphur on health?
Answer:
Animals exposed to sulphur suffer largely from the nervous system and brain damage as a result of the hypothalamus's dysfunction. Sulphur has been shown to seriously harm the veins in the brain, heart, and kidneys in laboratory testing using test animals. These investigations have also shown that certain sulphur compounds can have congenital and foetal harm effects. Even mothers can pass on sulphur toxicity to their offspring through breast milk.

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