How might you prepare(in one step) copper(II) nitrate from copper(II) chloride?

##2AgNO_3(aq) +CuCl_2(aq) rarr Cu(NO_3)_2(aq) + 2AgCl(s)darr##

The silver halide precipitates as a curdy white solid. Copper nitrate remains in solution. This is an expensive way to make copper salts.

A better means might be via the lead salt:

##Pb(NO_3)_2(aq) +CuCl_2(aq) rarr Cu(NO_3)_2(aq) + PbCl_2(s)darr##

At least this way you don't get silver salts, which have a tendency to reduce. ##PbCl_2## is fairly insoluble in cold water, and non-redox active.