检查硫酸盐时,以氯化钡溶液作为沉淀剂,为了除去CO32-,PO43-等离子的干扰,应在()条件下进行
A. 中性
B. 碱性
C. 稀硫酸酸性
D. 盐酸酸性
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在古蔡氏检砷法中,加入醋酸铅棉花的目的是()
A. 将五价砷还原为三价砷
B. 除去硫化氢的干扰
C. 除去锑化氢的干扰
D. 加快砷化氢生成的速度
重金属检查中,加入硫代乙酰胺时溶液控制最佳pH值为()
A. 2.5
B. 7.0
C. 3.5
D. 4.0
1. Whatisthepurposeofthispassage?
A.Toencouragemorepeopletousepublictransportation.
B. Tohelpyoumakeyourcommutebetter.
C.Toshowhowtostudyandcommuteatthesametime.
D.Toadvisereadersnottocommute.
2. Accordingtothepassage, whydopeoplespendmoretimecommutingto workandcollegenowadays?
A.Becauseit’sexpensiveforthemtorentapartmentsincities.
B.Becausecommutingisreallyrelaxingandfun.
C.Becausepublictransportationisverycheap.
D.Becausetheydon’thavetimetowalk.
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