“配制50mL约25%的粗食盐水”)
(2)步骤②中,SO42-是否需要除去?_______________,理由是: ________________________________________________________________
_______________________________________________________________
_______________________________________________________________; (3)步骤④中所有操作的共同目的是:____________________________
___________________________________________________________;;
(4)步骤⑤中晶体的洗涤液中主要含有的杂质阳离子是_____________
,在通常情况下,检验这种阳离子的方法是______________________
____________________________________________________________
____________________________________________________________ 。