SULPHUR [mod1).pptx_*hhhhhhhhhhhhhhhhhhh

Chemistry teaching of sulphur

1. SULPHUR AND ITS COMPOUNDS …

2. Sulphur is a non-metallic chemical element belonging to the oxygen group (Group 16 [ VIA] of the periodic table), one of the most reactive of the elements. Pure sulphur is a tasteless,  odourless , brittle solid  that is pale yellow in colour , a poor conductor of electricity, and insoluble in water. It is known for its medicinal value and its germicidal effect. It makes up about 0.1% of the earth’s crust. Its deposits are found in USA, Poland, New Zealand, Japan.

3. Extraction of sulphur by Frasch Process

4. The Frasch process is a method to extract sulphur   from underground deposits . The extraction process involves drilling a hole of about 30cm in diameter through the soil layers to the sulphur bed. A suphur pump made of three concentric steel pipes is then driven down the hole. In the process, superheated water ( about 170 ⁰C and 10 atm.) is pumped into the sulphur deposit. At 115 ⁰C, the sulphur melts.

5. Then hot compressed air at a pressure of 15atm is then blown down the innermost tube to force the molten sulphur up through the middle tube. The molten sulphur is continuously pumped into a vessel at the surface, where it is allowed to cool and solidify in large tanks. The Frasch process is able to produce high-purity sulfur. The sulphur obtained this way is 99.5% pure.

6. ALLOTROPES OF SULPHUR Allotropes of sulphur are classified into two: Crystalline allotropes Non-crystalline or Amorphous sulphur Crystalline allotropes are: Rhombic sulphur ( α - sulphur ) Monoclinic sulphur ( β - sulphur ) Amorphous sulphur ( δ - sulphur ) has no regular crystalline shape.

7. Rhombic sulphur Free sulphur exists as rhombic sulphur in nature because it is the only stable allotrope at temperatures below 96 ⁰C. Crystals of rhombic sulphur are bright yellow and octahedral. They are made up of S 8 molecules which exists as eight atoms. Rhombic sulphur is prepared by allowing a saturated solution of sulphur in carbon (IV) sulphide to evaporate slowly. Octahedral crystals will gradually be deposited.

8. Note: The preparation of rhombic sulphur should be done in a fume cupboard because carbon (IV) sulphide is highly flammable and very poisonous.

9. Monoclinic sulphur Monoclinic sulphur is the only stable allotrope of sulphur at temperatures between 96 ⁰C and 119 ⁰C . The crystals are long, thin and needle-shaped. They consist of S8 molecules. At room temperature, it slowly reverts to rhombic sulphur . Monoclinic sulphur is prepared 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.

10. 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 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. These crystals appear as prisms; hence we can call these crystals as prismatic sulphur .