Silicon Tetrachloride

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 Si_nCl_2n+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.