2Fe + 6H2SO4 đ -> to Fe2(SO4)3 + 3SO2 + 6H2O
x------------------------------------------------- 1,5 x
Mg + 2H2SO4 đ -> to MgSO4 + SO2 + 2H2O
x------------------------------------------x
nFe = nMg = x mol
nSO2 = 16/64 = 0,1875 mol
=> 1,5x + x = 0,1875
=> x= 0,075 mol
=> a = mMg + mFe = 0,075 . (24 + 56) = 6 g