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【简答题】
海水经过晒盐后得到粗盐和苦卤,重结晶后的食盐中还含有硫酸钠、氯化镁、氯化钙等可溶性杂质,他们在溶液中主要以SO 4 2- 、Ca 2+ 、Mg 2+ 的形式存在,为将这些杂质离子除净,应加入过量的氯化钡、氢氧化钠、碳酸钠等物质将其转化为沉淀,过滤除去;再加入适量的盐酸,得到精盐水,最后经蒸发即得精盐.以下是某化工厂对海水进行综合利用的示意图: (1)在苦卤制镁的过程中加入了石灰乳(主要成分是氢氧化钙),石灰乳是用生石灰制得的,请写出制取石灰乳的化学方程式______. (2)在制备精盐的过程中,氯化钡和碳酸钠溶液的添加顺序是否可以颠倒______,理由是______; (3)在利用粗盐制备精盐过程的第⑥步操作中,加入适量盐酸的目的是______.
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