Re: Density of a penny

Density of a solid (esp. a crystal) depends greatly on the structure. One 
should be clear that penny is a piece of zinc electroplated with copper! 
Electrochemical baths are basically solution-solid interfaces. when Cu 
comes to the surface of zinc, it actually induces oxidation of Zn to its 
oxide because of the large difference between the electronegativity of Zn 
and Cu! This oxygen interference would be little in terms of mass but 
would affect the density to a significant extent. Thus the apparent 
density of the coin seems reduced than the parent ingredients.

Please mail to raghu.cecri@gmail.com if you still have doubts!