(1)铁在置换反应通常 0 ==>+2!Fe + CuSO4 == FeSO4 + Cu(2)复分解反应中不变价，+2，+3！FeSO4 + 2NaOH == Fe(OH)2 + Na2SO4Fe2(SO43 + 6NaOH == 2Fe(OH)3 + 3Na2SO4
