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Sulphur and its Allotropic Forms

Last updated date: 27th Feb 2024
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Introduction to Sulphur and its Allotropic Forms

This topic educates the students on Sulphur, including its allotropic forms. In the periodic table, sulphur can be found in group 16. 0.17 % of the earth's crust, which consists of sulphur. It is non-metal and can be obtained as a by-product after natural gas production.

Let us understand more details about Sulphur and its Allotropic Forms from this article.

Properties of Sulphur

Let us look at the important physical and chemical properties of the sulphur compound.

Physical Properties

  • Sulphur looks yellow in colour.

  • This compound is insoluble in water. But, it is much soluble in toluene (which is methylbenzene) and carbon disulphide.

  • It is non-metal and therefore, it is defined as a poor conductor of electricity and heat.

  • At a point, where we consolidate Sulphur vapour, we get a fine powder that shapes a pattern resembling a flower. This is referred to as the 'Flower of Sulphur'.

Chemical Properties

  • Under specific conditions, most of the metals and non-metals react with Sulphur.

  • Sulphur burns in excess of air with a bright blue fire and produces Sulphur (IV) oxide and some amount of Sulphur (VI) oxide.

  • This compound reacts with Hydrogen at very high temperatures and produces hydrogen sulphide.

  • Sulphur vapour also reacts with hot coke to form a fluid, carbon disulphide.

Allotropic Forms of Sulphur

Sulphur produces several allotropes, but let us study the two most essential allotropes of sulphur in detail.

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One is the yellow rhombic sulphur (α-sulphur), and the other is monoclinic (β-sulphur). The most interesting feature is that the thermal stability and the allotropes of the sulphur compound are interconvertible. It means rhombic sulphur, when heated more than 369K produces monoclinic sulphur. Let us discuss these both allotropes in detail.

Types of Sulphur

  1. Rhombic sulphur (α-sulphur)

Rhombic sulphur is defined as a crystalline in nature and has an octahedral shape. On heating the roll sulphur solution present in the CS2, we get rhombic sulphur. It is yellow in colour with a specific gravity 2.06 and melting point of 385.8K. Rhombic sulphur compounds cannot be dissolved in water, but they can be dissolved in ether, benzene, or alcohol.

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  1. Monoclinic Sulphur (β-sulphur)

When we melt rhombic sulphur using a dish, we obtain monoclinic sulphur after cooling it. In this specific process, we put two holes in the crust and pour out the rest of the liquid. After this process, when the crust is removed, we get the colourless needle-shaped crystals of β-sulphur.

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  1. Colloidal Sulphur

We can make this type of sulphur by passing hydrogen sulphide through the saturated and cooled solution of the sulphur dioxide in water. The other method can be achieved by including an alcohol and sulphur solution in the water.

It also acts as a solvent in the carbon disulfide.

We can utilise this compound as a part of medicines.

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  1. Milk of Sulphur

We can make this type of sulphur by the action of weak hydrochloric acid on the ammonium sulphide. In a similar process, this milk of sulphur is produced by the boiling of sulphur with calcium hydroxide (which becomes an aqueous solution). We can filter this mixture and add the weak hydrochloric acid to produce sulphur milk.

This compound is given as a non-crystalline, and it looks white in colour.

At the point when we heat this compound, it changes to the conventional yellow colour of sulphur that we can use as a part of medicines.

It is soluble in carbon disulphide.

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Do You Know the Reason Why 369K is Known as a Transitional Temperature?

369K is known as transition temperature because both the sulphur's allotropes are stable at this temperature. In other terms, we can conclude that α sulphur is completely stable below 369K and it also becomes β-sulphur above that particular temperature.

Rhombic and monoclinic sulphur both contain S8 molecules. The alternative packing of the S8 molecules produces multiple crystal structures.

Stable Allotropic form of Sulphur

Sulphur is mostly found in two allotropes: rhombic and monoclinic. The most stable allotrope of Sulphur is the Rhombic allotrope (yellow in colour).

When this stable allotrope of Sulphur, the Rhombic form, is heated to a temperature greater than 370 K, the Rhombic form is changed to Mono clinic.

Uses of Sulphur

Let us look at the important uses of sulphur, as listed below:

  • We can use sulphur compounds to develop specific sorts of fungus in the vines.

  • Sulphur is defined as a common ingredient in the formation of tetraoxosulphate(VI) acid. We can also say that this is the essential use of sulphur.

  • We can use sulphur in the preparation of calcium hydrogen tetraoxosulphate (IV), Ca(HSO3)2. Here, this compound also finds its use as a wood pulp bleacher in the paper manufacturing industry.

  • Sulphur is an important and common ingredient in rubber vulcanisation. This method involves making the rubber hard and tough by binding the rubber molecules close to one another.

  • We use sulphur in the manufacturing of dyes.

  • Sulphur is quite common in the fabrication of sulphur compounds—for example, CS2 and sulphur monochloride, carbon disulfide, S2Cl2.

  • It finds its significant usage in ointments.

  • Sulphur is also an essential ingredient in the sulphides such as phosphorus sulphide. We can use this as a part of making gunpowder, matches, and firecrackers.

FAQs on Sulphur and its Allotropic Forms

1. Give the Importance of Sulphur?

Sulphur has gained special importance due to its uses. Its uses are not simply limited to the industries but also plays a crucial role in our ecosystem by affecting the plant's growth. This has led to the development of several sulphurs containing fertilisers.

2. What is a Y-sulphur ?

Y-sulphur was prepared by F.W. Muthmann for the first time in 1890. At times, it is called either "mother of pearl sulphur" or "nacreous sulphur" due to its appearance. This compound crystallises in pale yellow monoclinic needles. It holds puckered S8 rings such as α-sulphur and β-sulphur and only varies from them in the way that these rings are packed.

This is the densest form of the three. It is prepared either by cooling molten sulphur  slowly that has been heated more than 150 °C or by chilling the solutions of sulphur in ethyl alcohol, hydrocarbons or carbon disulfide. It is naturally found in nature as mineral rosickyite.

3. What is Amorphous sulphur?

Amorphous sulphur is defined as the quenched product of sulphur that melts above 160°C (at this point, the liquid properties melt and change remarkably. For example, a large increase in viscosity). Its form gradually changes from an initial plastic to a glassy form. Thus its other names are given as glassy, vitreous, or plastic sulphur. It is also referred to as χ-sulphur. It holds a complex mixture of catena-sulphur, which forms mixed with cyclo-forms.

4. What is Insoluble sulphur?

Insoluble sulphur can be obtained by washing the quenched liquid sulphur with CS2. Sometimes, it is also called polymeric sulphur, ω-S or μ-S.

5. Why has Sulphur gained importance?

Sulphur's importance has grown as a result of its applications. Its applications are not confined to industry; it also plays an important function in our ecology by influencing plant growth. As a result, various sulphur-based fertilisers have been developed.