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.

Explanation

(a) Silicon upon heating with methyl chloride to about `300^(@)C` in the presence of copper catalyst reacts as follows:
`2CH_(3)Cl(g)+Si(s)overset(Cu//300^(@)C)rarr(CH_(3))_(2)SiCl_(2)(l)`
The compound upon hydrolysis leads to the formation of silicon polymers. for more details, consult Section 11.11.
(b) On reacting silicon dioxide with hydrogen fluoride, silicon tetrafluoride `(SiF_(4))` is formed.
`SiO_(2)+4HFrarrSiF_(4)+2H_(2)O`
`SiF_(4)` reacts further with hydrogen fluoride to form hydrofluorosilicic acid.
`SiF_(4)+2HFrarrH_(2)SiF_(6)`
( c) ZnO is reduced to Zn by CO which is a strong reducing agent.
`ZnO+COoverset("Heat")rarrZn+CO_(2)`
(d) The two compounds react upon heating under pressure to form a soluble complex.
`Al_(2)O_(3)(s)+2Na(OH)(aq)+3H_(2)O(l)rarr2Na[Al(OH)_(4)](aq)`