COMPOUNDS

 COMPOUNDS

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SULPHUR: Sulphur has been known for it’s medicinal value and its germicidal effects since 1000 B.C. However ,it’s chemical nature remained unknown until 1787 and when Lavoisier recognized it as an element. Sulphur makes up about 0.1% of the earth’s crust. It occurs freely as deposits in USA, Poland, Japan,New Zealand and Sicily. It is also widely found in the combined state as sulphide of iron, zinc, lead, copper and mercury, and as the tetraoxosulphate (vi)salts of calcium, magnesium and barium. Meanwhile Sulphur is also present in many proteins.

EXTRACTION OF SULPHUR

Most of the world’s sulphur is obtained from underground deposits which may be more than 200m below the surface of earth . Extraction of sulphur from these deposits is based on the frasch process. A hole , that is about 30cm in diameter, is drilled through soil layers to the sulphur bed. A sulphur pump made up of three concentric steel pipes is then driven down the hole . Super_heated water at about 170°C and 10atm pressure is forced through the outermost tube to the sulphur bed to melt the sulphur (,melting point115°C). The Hot compressed air at a pressure of about 15atm is been blown down the innermost tube to force the molten sulphur up through the middle tube . Meanwhile the molten sulphur is continuously pumped into receptacle at surface where it allowed to solidify in large tanks. The sulphur obtained is about 99.5% pure.

Natural gas contains a small amount of hydrogen sulphide. The hydrogen sulphide is first separated out by mixing it with air and passing it over a heated aluminum oxide (AI2O3) catalyst.

2H2S(g) +O2(g),__>2H2O +2S(s)

ALLOTROPES OF SULPHUR

The main allotropes of sulphur are rhombic sulphur and monoclinic or prismatic sulphur, which are crystalline, amorphous sulphur. There is another form known as plastic sulphur.

Rhombic sulphur: Free sulphur exists as rhombic sulphur in nature because it is the only stable allotrope at temperatures below 96°C. Crystal of rhombic sulphur are bright yellow and octahedral. They are made up of S8 molecules. Each S8 molecules consist of a ring of eight atoms. However the Rhombic sulphur is being prepared by allowing a saturated solution of sulphur in carbon (IV)sulphide to evaporate slowly. Octahedral crystals will gradually be deposited.

MONOCLINIC SULPHUR: Monoclinic sulphur is the only stable allotrope at temperatures between 96°C and 119°C. The crystals are long, thin ,and needle_shaped, and consist of S8 molecules. Furthermore at the room temperature, they slowly turn to rhombic sulphur crystals. Monoclinic sulphur is less dense this rhombic sulphur. This is because the S8 molecules are more tightly packed in rhombic sulphur than in Monoclinic sulphur.

Monoclinic sulphur is obtained by cooling molten sulphur. Heat some powdered sulphur in a crucible till it melts. Add more sulphur and continue heating and stirring it at the same time. Repeat this process until the crucible is almost filled with molten sulphur. Then allow the molten sulphur to cool

After some time, a hard crust will be formed at the top. Pierce two holes through the crust and pour off the remaining molten sulphur from inside before removing the crust. Needle_Shaped crystals of Monoclinic sulphur can be found as deposits on the sides of the crucible.

The following relationship exists between rhombic and Monoclinic sulphur.

AMORPHOUS SULPHUR

Amorphous sulphur has no regular crystalline shape. Meanwhile, It is prepared as a pale yellow, and it is almost white deposit when hydrogen sulphide is bubbled through water for a long period of time and the saturated solution is exposed to air. However, have It in mind that is also deposited in chemical reactions. e.g. by the action of dilute hydrochloric acid on a trioxothiosulphate (VI) solution.

PLASTIC SULPHUR

Plastic sulphur is a supercooled form of sulphur. If yellow sulphur is heated and poured into cold water. Bear in mind that It will roll up into yellow ribbons which looks as if they are created by plastic material. moreover, Note It is soft and elastic and can not dissolve in carbon (IV)sulphide. However, the Plastic sulphur is generally not considered to be a true allotrope of sulphur because of it’s unstable and reverts to rhombic sulphur on standing.

PHYSICAL PROPERTIES

1. Sulphur is a yellow solid . it exist in two forms amorphous and crystalline.

2. It is insoluble in water but soluble in carbon (IV)sulphide and methyl benzene (toluene).

3. Being a non_metal, sulphur is a bed conductor of heat and electricity.

4. Density depends on allotropic form.

5. It has a melting point of 119°C and a boiling point of 444°C.

EFFECT OF HEAT

When sulphur is heated in a limited amount of air, it melts at temperatures between 115°C and 119°C into an amber coloured liquid. The colour darkens as the temperature increases. At about 160°C, the liquid becomes very dark and starts to turn viscous, reaching its maximum viscosity at 200°C. On further heating, it begins to flow again, and boils to give off a light brown sulphur vapour at its boiling point of 444°C. When this vapour is condensed on a cold surface, a fine powder which forms a floral pattern is obtained. This is flowers of sulphur. Molten sulphur is often poured into tubular moulds to form roll sulphur.

CHEMICAL PROPERTIES

sulphur like oxygen, belongs to Group 6 of the Periodic Table. However the sulphur atom has only six valence electrons like oxygen atom. In order to achieve an actet structure, it gains two electrons, usually from Groups 1 and 2 metals, to form the divalent sulphide ion,S2-. With non metals, sulphur attains the octet structure by sharing electrons to form covalent compounds such as hydrogen sulphide, H_S_H. The oxidation States of sulphur can range from_2 to +6.

DIRECT COMBINATION WITH OTHER ELEMENTS

Nearly all metals and most non metals combine directly with sulphur.

With metals: Sulphur combines directly with many metals to form sulphides when heated in the absence of air. Reactive metals like sodium and potassium may even react with sulphur spontaneously without heating,if both the metals and the sulphur are in a finely divided form.

With Oxygen: When sulphur is heated in a plentiful supply of air , it burns with a bright blue flame to form sulphur (IV) oxide and a small amount of sulphur (VI) oxide. O2(g)+S(g)__>SO2(g).

With Hydrogen: At high temperatures, sulphur combines slowly with hydrogen to form hydrogen sulphide. The reaction is more rapid if hydrogen is bubbled through boiling sulphur.

With Carbon: Sulphur combines with coke in an electric furnace to form a colourless liquid known as carbon (iv)sulphide, which vaporizes readily , forming poisonous and highly flammable fumes.

With other non metals: Sulphur also combines with the other non metals in other to form various sulphides ,e.g. tetraphosphorous trisulphide ,disulphur dichloride and sulphur hexafluoride .

ACTION OF OXIDIZING ACIDS

The Sulphur is readily oxidized when being warmed with a concentrated tetraoxosulphate (vi)acid in other to form sulphur (iv)oxide. The acid itself is reduced to sulphur (Iv)oxide. When warmed with concentrated trioxonitrate( V) acid , using bromine as catalyst, sulphur is oxidized to tetraoxosulphate (VI)acid.

ACTION OF HOT CONCENTRATED ALKALIS

Sulphur will react with hot concentrated alkaline solutions to form a mixture of sulphides and trioxosulphate (IV) , which , in the presence of excess sulphur, react to form a polysulphide and a trioxosulphate (VI) respectively.

USES

1.Sulphur is used to produce sulphur(IV) oxide for manufacturing tetraoxosulphate (VI) acid.

2. Sulphur is also used in the vulcanization of rubber.

3. Sulphur and some of it’s products are also used as fungicides and insecticides for spraying crops in our farms.

4. Sulphur is used to manufacture the bleaching agent used for the production if carbon (IV)sulphide, skin ointments and dyes ,and as sulphides in manufacturing matches , fireworks and gun powder.

Sulfurs is used as a fungicide and in black gunpowder for the vulcanisation of natural rubber.It is used for making car batteries, fertilizer, oil refining, water processing, and mineral extraction. Meanwhile Other applications for sulfur-based chemicals include rubber vulcanization, bleaching paper, and product making such as cement, detergents, pesticides. And also some gunpowder.

Advantage of Sulphur to the skin:Sulfur helps to dry out the skin’s surface and help absorb excess oil (sebum) which can lead and acne breakouts. To help unblock your pores it also dries out dead skin cells. However, Some of the products contain sulfur along with other ingredients used to fight acne, such as resorcinol.

Note, that Sulfur is recovered from natural gas , coal, crude oil, and other sources such as flue dust and gasses which is from metal sulfide ores refining. However the Elemental sulfur is obtained in so many forms including sulfur flowers, fine crystalline powder and roll sulfur as well.

However, Sulfur, which is in the human body, is the third most abundant chemical. Meanwhile it’s factor is also present in a variety of foods, including garlic , onions, eggs and foods high in proteins. Sulfur is very necessary for the synthesis of the essential cysteine and methionine amino acids.

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