a/ nHCl = 0.25 
n khí = 0.11 
CaCo3 + 2HCl = CaCl2 + CO2 + H2O
x----------2x-----------x-------x 
Fe + 2HCl = FeCl2 + H2 
y-------2y----------y-----y 
Có: 
100x + 56y = 5.7 
x + y = 0.11 
=> x = 0.01
=> mCaCO3 = 1g
=> %Cu = 17.54% 
     % Fe = 82.46%