Question

Question 11.21 Explain the following reactions

(a) Silicon is heated with methyl chloride at high temperature in the presence of copper;

(b) Silicon dioxide is treated with hydrogen fluoride;

(c) CO is heated with ZnO;

(d) Hydrated alumina is treated with aqueous NaOH solution.

Class XI The p-Block Elements Page 324

Answer 1

Silicon is heated with methyl chloride at high temperature in presence of copper

Answer 2

(a) When Si is heated with CH3Cl at high temperature (570K) in the presence of Cu as a catalyst, a mixture of mono-, di- , and trimethylchlorosilanes along with a small amount of tetramethylsilane is formed.
e.g., CH3Cl + Si------(Cu,570K)---> CH3SiCl3
+ (CH)2SiCl2 + (CH)3SiCl + (CH3)4Si

(b) When SiO2 reacts with HF, silicon tetrafluoride is formed which dissolves in HF to form hydrofluorosilicic acid.
e.g., SiO2 + 4HF ------>SiF4 + 2H2O;
SiF4 + 2HF -----> H2SiF6

(c) CO is a strong reducing agent but it can't reduce ZnO as for CO---->CO2 ,∆G is always higher than that of ZnO . Thus, no reaction takes place.

(d) Alumina dissolves to form sodium meta - aluminate.
Al2O3.2H2O + 2NaOH ----> 2NaAlO2 + 3H2O