• # 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.

(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. $A{{l}_{2}}{{O}_{3}}\cdot 2{{H}_{2}}O+2NaOH\xrightarrow{Heat}2NaAl{{O}_{2}}+2{{H}_{2}}O$