redox reaction between zinc powder and aqueous copper nitrate?

Question

Zn (aq) + Cu(NO3)2 yields Zn(NO3)2 (aq) and Cu (s).

Why is the copper displaced by zinc black in color and not brown in color? The original copper powder is brown in color.

Answer 1

I suspect that there must be an oxide coating on the copper grains. This doesn't happen if you use iron filings and copper sulphate (or nitrate) solution - you get lovely brown copper powder.