Reactions of Silicon

1.Silicon reacts with nonmetals at high temperatures.

heat

Si + C SiC

heat

Si + O₂ SiO₂

heat

Si + 2Cl₂ SiCl₄

2.Silicon does not react with acids at low temperatures, except HF.

Si + 4HF SiF₄ + 2H₂

3.Silicon reacts with hot, strong base solutions to form silicates.

heat

Si + 2KOH + H₂O K₂SiO₃ + 2H₂

Important compounds of silicon

Silicon dioxide, SiO₂ is the stable compound of silicon. Its structure is similar to diamond. So, it is very hard like diamond. It melts at 1600 ⁰C. When it is cooled, it solidifies without crystallization and quartz glass is formed. Since the thermal expansion coefficient of quartz glass is very low, it is not affected when heated to high temperatures. Due to this property, it is used to make laboratory glassware, various lenses, lambs and etc.

It is insoluble in water and acids, except HF.

heat

SiO₂ + 4HF SiF₄ + 2H₂O

Silicon dioxide forms silicates when reacted with oxides.

heat

SiO₂ + MgO MgSiO₃

Silicates

a. Clay:Clays occur naturally as alumina silicate, H₄Al₂SiO₉.

b. Glass:Glass is a super cooled liquid.SiO₂ is used in the production of glass. Calcium carbonate (CaCO₃), sodium carbonate (Na₂CO₃) and sand (mainly SiO₂) are heated at high temperature and glass is formed.

Na₂O.CaO.6SiO₂ (glass)

c. Cement: A mixture of limestone (CaCO₃) and clay are pulverized (powdered) and then roasted at about 1500 °C. After that, the mixture is ground with little gypsum (CaSO₄.2H₂O) to very fine powder.

Uses of Silicon

• Elemental silicon is used to prepare silicone polymers.
• It is used to prepare electronic devices such as computer chips and transistors since it is a semi-conductor.
• Copper-silicon alloy is used in the preparation of telephone wires.
• Used in glass industry.
• Used in the production of cement.

Date: 2016-01-03; view: 937