熔沸点的测定

1、Melting Point and Boiling Point1. Purpose1.1 Learn the knowledge of melting point and boiling point.1.2 Grasp the methods to test melting point and boiling point with Capillary Tubes. 1.3 Grasp the usage of Digital melting-point apparatus. 2. Principle2.1 Melting PointDefinition: The melting point o

2、f a substance is defined as the temperature at which the liquid and solid phases exist in equilibrium with one another .Figure1. Phase change with time and temperatureSharp increase after melting, so heat slowlyIf heat is added to a mixture of the solid and liquid phases of a pure substance at the m

3、elting point, ideally no rise in temperature will occur until all the solid has melted and been converted to liquid.The melting point and freezing point of a pure substance are identical.A pure organic compound have a settled melting point, usually lower than 350, with a temperature range of 0.51 .F

4、igure2. The effects of impurities on melting pointAccording to Raoults law, at a certain pressure and temperature conditions, if we put solute into a solvent, the partial pressure of solvent vapor will obviously decreased. The solid and liquid phases intersect at points M1, which represents the boil

5、ing point of compounds containing impurities are lower than that of pure compounds. 当含杂质时（假定两者不形成固熔体），根据拉当含杂质时（假定两者不形成固熔体），根据拉乌耳定律可知，在一定的压力和温度条件下，在溶剂乌耳定律可知，在一定的压力和温度条件下，在溶剂中增加溶质，导致溶剂蒸气分压降低，固液两相交点中增加溶质，导致溶剂蒸气分压降低，固液两相交点M M 即代表含有杂质化合物达到熔点时的固液相平衡共即代表含有杂质化合物达到熔点时的固液相平衡共存点，存点，T T1 1为含杂质时的熔点，显然，此时的熔点较纯为含杂

6、质时的熔点，显然，此时的熔点较纯粹者低，熔点距扩大。粹者低，熔点距扩大。因此，熔点是判断晶体化合物纯度的重要指标之一。因此，熔点是判断晶体化合物纯度的重要指标之一。2.2 Melting point methods and apparatus(1) Capillary tubes and sample preparationCommercially available capillary tubes have one end already sealed and the other opened end to permit introduction of the sample（2-3mm）。）

7、。熔点管制备：熔点管制备：将毛细管一端用酒精灯烧熔封口，呈将毛细管一端用酒精灯烧熔封口，呈4545角，不角，不停旋转。停旋转。注意事项：注意事项：样品需研细，可填装结实，有空隙则不易传热，影响结果。样品需研细，可填装结实，有空隙则不易传热，影响结果。样品装实后样品装实后2 23mm3mm。样品装填需迅速，防治吸潮。样品装填需迅速，防治吸潮。样品只可用一次样品只可用一次 （2） Thiele tube apparatus12435Proper use of the Thiele tube is critical to obtain reliable melting points。Heating

8、rate. Firstly, the heating should be quickly. When the temperature is 1015 lower than the melting point, heat the Thiele tube at the rate of 12 /min in order to determine the melting point。 通过剪短灯芯或移远酒精灯通过剪短灯芯或移远酒精灯调节加热速度。调节加热速度。NotesFive important positions.（3） Melting point determination procedureM

9、elting invariably occurs over a temperature, and the melting point range is defined as the temperature at which the first tiny drop of liquid appears up to and including the temperature at which the solid has melted completely。Pay attention to the first tiny drop of liquid appear is the beginning of

10、 the melting process。2.3 Digital melting point apparatus开机稳定开机稳定20min设起始温度设起始温度（低于熔点（低于熔点10）放样放样（电流归零）（电流归零）升温（升温（1/min）初熔灯亮初熔灯亮出终熔温度出终熔温度降温后关机降温后关机2.4 Boiling PointDefinition: when the vapor pressure of the liquid being heated equals the atmospheric pressure on the surface of the liquid, it boils.

11、The temperature at that moment, is called boiling point.Figure4. The relationship between vapor pressure and boiling pointEvery pure organic compound has a fixed boiling point at a certain pressure.But sometimes an organic compound together with other components can form a binary or ternary azeotrop

12、e mixture(二元二元或三元共沸物或三元共沸物）, which also has a definite boiling point.沸点管分内管与外管，外管回收。沸点管分内管与外管，外管回收。外管内液体量理论为外管内液体量理论为1/5，实际装，实际装1/2，以免挥发损失。，以免挥发损失。内管长度为外管的内管长度为外管的2/3，开口端向下，但勿接触管底。开口端位，开口端向下，但勿接触管底。开口端位于温度计水银球中部。于温度计水银球中部。加热时，内管中会有小汽泡缓缓逸出，在达到沸点时，将有一加热时，内管中会有小汽泡缓缓逸出，在达到沸点时，将有一连串的小气泡快速地逸出。此时停止加热，连串的小气泡快速地逸出。此时停止加热，此时温度即为该液体的沸点。此时温度即为该液体的沸点。外管回收外管回收Figure 5 Micro Determina