2Al+3CuSO4->Al2(SO4)3+3Cu
x......1,5x..........0,5x............1,5x
Có
64.1,5x-27x=3,45=>x=0,05
mAl pứ=27.0,05=1,35g
nCuSO4pứ=1,5.0,05=0,075mol
nCuSO4bđ=0,5mol
nCuSO4dư=0,5-0,075=0,425mol
CM dd CuSO4 dư=0,425/0,5=0,85M
CM dd Al2(SO4)3=0,025/0,5=0,05M