Question

When vapours of ${\text{SiC}}{{\text{l}}_{\text{4}}}$ is passed over hot ${\text{Mg}}$ then the product formed is:
A. ${\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + MgC}}{{\text{l}}_{\text{2}}}$
B. ${\text{MgSi + C}}{{\text{l}}_{\text{2}}}$
C. ${\text{MgSiC}}{{\text{l}}_{\text{6}}}$
D. ${\text{Si + MgC}}{{\text{l}}_{\text{2}}}$

Answer 1

When Silicon tetrachloride is passed over hot Magnesium, ${\text{Mg}}$ acts as reducing agent by itself getting oxidised and brings about reduction i.e., it reduces ${\text{SiC}}{{\text{l}}_{\text{4}}}$ in the above reaction.

Complete answer:
A reducing agent is one which itself gets oxidised and bring about reduction
When vapours of ${\text{SiC}}{{\text{l}}_{\text{4}}}$ is passed over hot ${\text{Mg}}$. The ${\text{Mg}}$ will act as reducing agent i.e., it reduces ${\text{SiC}}{{\text{l}}_{\text{4}}}$ from +4 to ${\text{Si}}$ which is in 0 oxidation state and ${\text{Mg}}$ itself gets oxidised from 0 oxidation state to +2
The reaction is given as
${\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + Mg}}\xrightarrow{{}}{\text{Si + MgC}}{{\text{l}}_{\text{2}}}$

Hence, the correct answer is option D.

Additional information:
Silicon tetrachloride is a colourless fuming liquid with a freezing point of ${\text{ - 7}}{{\text{0}}^{\text{o}}}{\text{C}}$
${\text{SiC}}{{\text{l}}_{\text{4}}}$ is formed by the reaction of ${\text{Si}}$ with ${\text{C}}{{\text{l}}_{\text{2}}}$
${\text{Si + 2C}}{{\text{l}}_{\text{2}}}\xrightarrow{{}}{\text{SiC}}{{\text{l}}_{\text{4}}}$
It can also be prepared as
${\text{SiO + 2C + 2C}}{{\text{l}}_{\text{2}}}\xrightarrow{{{\text{1675 K}}}}{\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + 2C}}{{\text{O}}_{}}$
Commercially it is prepared as
${\text{Si + 4HCl}}\xrightarrow{{{\text{600 K}}}}{\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + }}{{\text{H}}_{\text{2}}}$
Reaction of ${\text{SiC}}{{\text{l}}_{\text{4}}}$ with ${{\text{H}}_{\text{2}}}{\text{O}}$
The reaction is exothermic, this is a hydrolysis reaction
${\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + 4}}{{\text{H}}_{\text{2}}}{\text{O}}\xrightarrow{{}}{\text{4HCl + }}{{\text{H}}_{\text{4}}}{\text{Si}}{{\text{O}}_{\text{4}}}$
Alcoholysis
When silicon tetrachloride is treated with ethanol we get the ester formation along with hydrochloric acid
${\text{SiC}}{{\text{l}}_{\text{4}}}{\text{ + }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}\xrightarrow{{}}{\text{Si}}{\left( {{\text{O}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}} \right)_{\text{4}}}{\text{ + HCl}}$

Note: Magnesium is a solid and is light, silvery white, moderately hard metallic element. It occurs in the form of many soluble salts. It burns in flame with bright white light and upon heating they react with halogens. Magnesium combines with oxygen at room temperature to form Magnesium oxide.