氯化钠提纯实验中几个重要问题的讨论

Discussion on Some Key Factors for Purification of Coarse Salt

氯化钠提纯实验是高校化学类各专业的典型实验,涉及基础化学实验中的称量、溶解、沉淀、pH值测定、常压过滤、减压过滤、蒸发浓缩、结晶干燥、离子定性鉴定等基本操作。本文讨论了氯化钠提纯实验中影响纯度的几个重要问题,分析了难溶盐BaSO_(4)、BaCO_(3)应该分步过滤除去的理论依据。研究表明,溶液酸度控制在pH=2~3可以完全除去溶液中的过量Na_(2)CO_(3);溶液中少量K^(+)在蒸发浓缩、减压过滤时除去。通过上述步骤,可以得到纯度级别非常高的精盐。

Sodium chloride purification is a typical experiment for college students of chemistry concerned majors,which involves basic chemical experimental procedures,including weighing,dissolution,precipitation,pH measurement,atmospheric pressure filtration,vacuum filtration,evaporation and concentration,crystallization and drying,ion qualitative identification,and so on.Several key factors that affected the purification of coarse salt were discussed.The reasons that using a step filtration process to remove the undissolved BaSO_(4) and BaCO_(3) were discussed in detail.It was found that the excessive Na_(2)CO_(3) in the solution could be entirely separated under pH of 2~3 and the small amount of potassium ions could be removed during the steps of evaporation condensation and decompression filtration.After these steps,refined sodium chloride was obtained.