Question: I read that:

> 
> Take a cupful of water in a beaker and add a few drops of dilute
>  sulfuric acid. Heat the water. When it starts boiling add copper
>  sulfate powder slowly while stirring continuously.
>  Continue adding copper sulfate powder till no more powder can be
>  dissolved. Filter the solution. Allow it to cool. Do not disturb the
>  solution when it is cooling. Look at the solution after some time. Can
>  you see the crystals of copper sulfate? If not, wait for some more
>  time.
> 
> 
> 

So why is sulfuric acid required in this experiment?

Answer: 
As stated previously, it is due to the head-on overlap of sigma bonds and the lateral overlap of pi-bonds.

The smaller overlap of pi bonds also explains why double and triple bonds basically exist only for 2nd row elements (C,N,O especially) and not for higher row elements. A C=C bond has a length of 133 pm. A Si-Si bond length is at around 186 pm, therefore the contribution of the pi-integral overlap is almost negligible. 

The inability of Silicium to form strong pi bonds is also one of the answer why life on earth is carbon based and not silicium based, since the richness of organic chemistry is in part due to the ability of carbon to form strong double and triple bonds.
Unsaturated compounds (due to the existence of a double bond) are more reactive than saturated compounds, because the electron density at the internuclear axis is zero in a pi bond (in contrast to the sigma bond).