【分析】 因为NaCl的量多,而
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/5bafa40f4bfbfbedb1a7c4eb6af0f736aec31fa3?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
的量少,且二者的溶解度相差很大(
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/4afbfbedab64034f64333092bdc379310b551da3?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
)的溶解度受温度的变化影响较大,NaCl的溶解度受温度的变化影响较小),故可根据不同物质在同一溶剂里的溶解度的差异,用蒸发结晶法提纯NaCl。 1、其操作步骤与基本原理为:(1)把混有少量
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/024f78f0f736afc366f2cdf1a119ebc4b64512a3?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
的NaCl晶体溶于适量的水中,制成NaCl的饱和溶液。(2)在较高温度下蒸发溶液,使NaCl结晶析出。因为NaCl的溶解度受温度变化影响较小(20℃时36g,100℃时40g),加热蒸发时容易达到饱和,而
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/aec379310a55b319c90770e151a98226cefc17a3?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
的溶解度受温度变化影响较大(20℃时31.6g,100℃时246g),且
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/eac4b74543a98226e93fd9b39882b9014b90ebac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
的含量又少,蒸发时不易达到饱和,所以,在蒸发溶液时,NaCl会部分结晶析出,而
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/42a98226cffc1e17a2417ea55890f603728de9ac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
却留在母液里。待大量晶体析出后,立即趁热过滤,即得较纯的NaCl晶体。
【点评】 解答本题时应利用NaCl和
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/8b82b9014a90f6035f4e6ed32b12b31bb151edac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
的溶解度受温度的影响不同而采用不同的结晶法。NaCl中含少量
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/f703738da97739129cd877f5ea198618377ae2ac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
,提纯NaCl时用蒸发结晶法,如果
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/b21bb051f819861805b91d1058ed2e738ad4e6ac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
中含少量NaCl,提纯
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/8718367adab44aed18b04c70a11c8701a08bfbac?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
时应用降温结晶法。