Explain the following.
Silicon is heated with methyl chloride at high temperature in the presence of copper.

Explanation

`to` Methyl chloride reacts with silicon at high temperature in presence of copper catalyst to form various types of methyl substituted chlorosilane.of formula` MeSiCl_(2),Me_(3)SiCl` with small amount `Me_(4)Si`
`to` Hydrolysis of dimethyl dichloro silane followed by condensation polymerisation forms a straight chain polymer (silicone) (Me=`CH_(3)`-group)
`2CH_(3)Cl+Sioverset(Cu)underset(573K)to (CH_(3))_(2)SiCl_(2)underset(-2HCl)overset(+2H_(2)O)to(CH_(3))_(2)Si(OH)_(2)`

`SiO_(2)` is treated with HF to form `SiF_(4)` which on hydrolysis to form `H_(4)SiO_(4)` and `H_(2)SiF_(6)`
`SiO_(2)+4HFtoSiF_(4)+2H_(2)O`
`SiF_(4)+4H_(2)OtoH_(4)SiO_(4)+2H_(2)SiF_(6)`
c)Graphite is soft and it has layer lattice. In this structure one of the layer slided over another due to weak Vander Waals force of attraction. These layers are slippery. Hence it is greasy and function as lubricant.
d) The covalent bonds in diamond are very strong and difficult to break, Hence diamond is used as an abrasive for sharpening hard tools, in making dyes and in the manufacturing of tungsten filaments etc.