question_answer 29)

Explain the following reactions : (a) Silicon is heated with methyl chloride at high temperature in presence of copper. (b) CO is heated with\[ZnO\]. (c) Silicon dioxide is treated with hydrogen fluoride. (d) Hydrated alumina is treated with aqueous \[NaOH\]solution.

Answer:

(a) When methyl chloride reacts with silicon in the presence of copper as a catalyst at a temperature of\[300{}^\circ C\], various types of methyl substituted chlorosilanes of formula \[C{{H}_{3}}SiC{{l}_{3}}\], \[{{(C{{H}_{3}})}_{2}}SiC{{l}_{2}},{{(C{{H}_{3}})}_{3}}SiCl\]and\[{{(C{{H}_{3}})}_{4}}Si\] (very small amount) are formed. \[C{{H}_{3}}Cl+Si\xrightarrow[300\,{}^\circ C]{Cu\,powder}C{{H}_{3}}SiCl\] \[+{{(C{{H}_{3}})}_{2}}SiC{{l}_{2}}+{{(C{{H}_{3}})}_{3}}SiCl+{{(C{{H}_{3}})}_{4}}Si\] (b) The reduction of \[ZnO\]into Zn metal occurs. \[ZnO+CO\to Zn+C{{O}_{2}}\] (c) Silica reacts with hydrogen fluoride and forms silicon tetrafluoride. \[Si{{F}_{4}}\] further reacts with HF and forms hydrofluorosilicic acid. \[Si{{O}_{2}}+4HF\to Si{{F}_{4}}+2{{H}_{2}}O\] \[Si{{F}_{4}}+2HF\to {{H}_{2}}Si{{F}_{6}}\] (d) Hydrated alumina dissolves to form sodium meta-aluminate. \[A{{l}_{2}}{{O}_{3}}\cdot 2{{H}_{2}}O+2NaOH\xrightarrow{Heat}2NaAl{{O}_{2}}+2{{H}_{2}}O\]