3Cu+ 8HNO3(稀) = 3Cu(NO3)2 + 2NO↑+4H2O
0.4 * 0.1 mol 3 * 0.4 * 0.1/8
n(Cu2+)= 0.015 mol
c(Cu2+)= 0.015 / 0.1 = 0.15 mol/L