Preparation
Silicon tetrachloride is prepared by heating either silicon or silicon carbide with chloride.
Si (s) + 2 Cl2 (g) ——> SiCl4 (l)
SiC(s) + 4 Cl2 (g) ——-> SiCl4 (l) + CCl4 (l)
Properties
1) It is a volatile liquid , b.p. 330.57 K.
2) Hydrolysis
Hydrolysis of SiCl4 gives silicic acid , Si(OH)4 which upon further heating undergoes partial dehydration to give silica gel.
SiCl4 (l) + 2 H2O (l) ——-> Si(OH)4 ——-> SiO2 .x H2O
Silica gel is amorphous and very porous.It contains 4% water, It is used as a catalyst in petroleum industry and as an adsorbent in column chromatography.
If hydrolysis of SiCl4 is carried out at high temperature then finely powdered silica is obtained.
SiCl4 (g) + 4 H2O (l) ———-> SiO2 (s) + 4 HCl (g)
3) Reduction
Reduction of SiCl4 with dihydrogen gives silicon.
SiCl4 (g) + 2 H2 (g) ———-> Si (s) + 4 HCl (g)
4) Reaction with silicon
Pyrolysis of SiCl4 with Si gives a series of perhalosilanes of the formula SinCl2n+2 where n=2-6.
SiCl4 + Si ———> Si2Cl6 + higher members of the series
These chains are longer than those formed by hydrides.This is due to additional pπ-dπ bonding between lone pairs of electrons present on Cl and empty d-orbitals of Si.
Uses
It is used to prepare ultrapure silicon used for making transistors , computer chips and solar cells.