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) A mixture of mono-, di - and trimethlychlorosilanes along with a small amount of tetramethylsation is formed.
`underset(" Methyl chloride ")(CH_(3)Cl) + Si underset(570K)overset("Cu powder ") rarr CH_(3)SiCl_(3) + (CH_(3))_(2)SiCl_(2) + (CH_(3))_(3)SiCl + (CH_(3))_(4)Si`
(b) The initially formed silicon tetrafluoride dissolves in `HF` to form hydrofluorosilicic acid
`SiO_(2) + 4 HF rarr SiF_(4) + 2H_(2)O` , `SiF_(4) + 2HF rarr H_(2)SiF_(6)`
(c ) `ZnO` is reduced to zinc metal.
`ZnO + CO rarr Zn + CO_(2)`
(d) Alumina dissolves to form sodium meta-aluminate
`underset("or Bauxite ")underset(" Hydrated aluminia ")(AlO_(3).2H_(2)O(s)) + 2NaOH(aq) overset("Heat")rarrunderset(" Sod. meta-aluminate ")(2NaAlO_(2)) + 3H_(2)O`
or `Al_(2)O_(3).2H_(2)O(l) + 2NaOH (aq) + H_(2)O(l) overset("Heat")rarrunderset(" Sod. tetrahydroxoaluminate (III)")(2Na[Al(OH)_(4)](aq))`