Q.Explain the following reactions

1. $2\text{CH}_3\text{Cl} + \text{Si} \xrightarrow[570\text{K}]{\text{Cu}} (\text{CH}_3)_2\text{SiCl}_2$.
2. $\text{SiO}_2 + 4\text{HF} \rightarrow \text{SiF}_4 + 2\text{H}_2\text{O}$, then $\text{SiF}_4 + 2\text{HF} \rightarrow \text{H}_2\text{SiF}_6$.
3. $\text{ZnO} + \text{CO} \xrightarrow{\Delta} \text{Zn} + \text{CO}_2$. …

1. (a) Silicon + methyl chloride, heated with Cu. Silicon reacts with methyl chloride vapour at about 570 K in the presence of a copper catalyst (the Rochow process) to form a mixture of methylchlorosilanes, the key precursors for silicone manufacture; the major product is dimethyldichlorosilane:

2. (b) Silicon dioxide + hydrogen fluoride. SiO$_2$ is unusual among common oxides in that it is attacked by HF (this is why HF is used to etch glass, and must be stored in wax/plastic, not glass, containers). It first forms silicon tetrafluoride, which reacts with further HF to give hexafluorosilicic acid:

3. (c) CO heated with ZnO. Carbon monoxide is a good reducing agent at high temperature; it reduces ZnO to metallic zinc, itself being oxidised to CO$_2$: $\text{ZnO} + \text{CO} \xrightarrow{\Delta} \text{Zn} + \text{CO}_2$ …

Recognise each part as a standard named reaction of p-block chemistry: (a) the Rochow (copper-catalysed) synthesis of methylchlorosilanes;

(b) SiO$_2$'s unique reactivity with HF used for glass etching;

(c) CO as an industrial reducing agent for metal oxides; …

• Forgetting the catalyst (Cu) and temperature condition are essential parts of the Si + CH$_3$Cl reaction, not incidental details. …