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1、熔沸点的测定（Determination of melting point）Experiment C-3 determination of melting pointObjective: 1. To study the principle of melting point determination, the application and the factors affecting the determination results.2 、 study the use of capillary and charging method.With Sarkozy tube 3, to deter
2、mine the melting point.Experimental principle: the melting point of a substance is the temperature at which the solid-liquid two-phase vapor pressure is equal at a given pressure, that is, the temperature at which the solid phase coexists with the liquid phase. Pure solid organic compounds usually h
3、ave a fixed melting point, which is under a certain pressure and heated to near the melting point, the change of solid-liquid two-phase between very sensitive, from the beginning to melt completely melted, the temperature change is generally not more than 0.5 to 1 DEG C. Substances containing impuri
4、ties tend to have lower melting points than pure ones, and the melting process has a greater temperature change. This is of great value in the identification of pure solid organic compounds, and the purity of the compounds can be qualitatively determined according to the length of the melting proces
5、s.Experimental procedure:(1) preparation of melting point tubes1. drawn capillary. With the sample loaded capillary, and its diameter is 1 1.2mm, 40 50mmlong if Sarkozy melting point tube, a length of about 70 75mm. The best wear out tube or pipe for capillary tube drawing 10mm thin glass. To draw t
6、he capillary before, should put the tube (or glass tube) with chromic acid and distilled water washed and dried, because cannot be pulled into a capillary cleaning.Methods: hands to draw the capillary glass tube, rotary heating in strong oxidizing flame, which fully burning soft dark cherry red. The
7、 glass tube moves away from the flame, and then began to slow, fast and elongated, reciprocating rotating glass tube, until pulled into an outer diameter of 1 to 1.2mm of the capillary, trombone, pay close attention to the thickness of the capillary. The drawn capillary tube is cut at two times the
8、required length, and the ends are fused at the edge of the small flame to close (the closed tube bottom is thin) so as not to leave dust in storage. When the utility model is used, the capillary pipe is cut off in the middle, and then two melting points pipes are formed.2. loading of sample0.1 0.2g
9、dry powder on the surface of sample dish into a small pile of pile, the melting point of the open end of the tube inserted in the sample, take a small amount of powder. The melting point of pipe erected on the desktop at a few (melting point tube must fall direction perpendicular to the desktop, or
10、melting point tubes are easy to fracture), the sample into the bottom of the tube. Repeat the material several times. The melting point of pipe from a length of about 40 50cm high glass tube fell into the dish, repeated several times, so that the sample at the end of the pipe tightly together. The s
11、ample must be uniform and strong. The sample height is about 2 3mm.3. instrumentationFigure C-3-1, figure C-3-2Sarkozy will clamp the iron, pour in the liquid bath bath for easy heat conduction, high level side tube about 0.5cm. The thermometer with a notched single hole cork fixed on Sarkozy tube.
12、Then use the thermometer mercury ball dipped in a small amount of bath, will be installed to the melting point of the sample tube carefully wetting, adhesion on the thermometer side, can also use the latex tube is made of a thin shear rubber ring is fixed on the thermometer and the central tube in t
13、he sample melting point thermometer mercury ball. The rubber ring is higher than the profit level and the rubber bath bath, in order to avoid contact. The thermometer into the Sarkozy tube in the middle depth of mercury ball just at the midpoint of the two sides of the pipe line at Sarkozy prevail.T
14、he thermal conductivity of liquid bath, usually with concentrated sulfuric acid, glycerol and liquid paraffin. Which option is selected depends on the required temperature two. If the temperature is below 140, it is better to use liquid paraffin or glycerin. Medicinal liquid paraffin can be heated t
15、o 220 degrees, still does not change color. The need to be heated to 140 degrees above, but also by concentrated sulfuric acid, hot concentrated sulphuric acid is very corrosive, if used improperly, concentrated sulfuric acid spilled easily hurt. Therefore, when measuring the melting point, wear gog
16、gles.The temperature exceeds 250 degrees, and the concentrated sulfuric acid gives off white smoke, which hinders the reading of temperature. In this case, potassium sulfate can be added to the concentrated sulfuric acid to heat it to a saturated solution,Then the measurements were made.The use of c
17、oncentrated sulfuric acid in a hot bath, sometimes due to organic matter falls into acid and black, interfere with the observation of the sample melting process. In this case, some potassium nitrate crystals can be added to remove organic matter.4. determination methodIn order to accurately determin
18、e the melting point, the heating time, especially in the heating to the melting point close to the sample, must make the temperature rise slowly and evenly. For each sample, at least for two times. For the first time, the temperature can be increased rapidly, and the temperature can be increased by
19、5 degrees per minute. Thus an approximate melting point can be obtained. Then took a hot bath to cool down, change a loaded sample tube made of second determination of melting point.Second melting point determination, at the beginning (starting fast rise Wenk per minute rise 10 degrees, later reduce
20、d to 5 DEG C), when the temperature in order to approximate the low melting point of about 10 DEG C, then a small flame, so that the temperature rise slowly and evenly (every 1 DEG C), material changes in test tube observe the melting point, melting point tube record has just appeared in small dropl
21、ets of liquid and sample exactly the two melting temperature readings. The more pure the material, the smaller the difference between the two temperatures. If the temperature is too high, the range of the melting point is not correct.When recording the melting point, the temperature at which the ini
22、tial melting and the full melting are recorded, such as 123125 degrees centigrade, must not be recorded only for the average of the two temperatures, such as 124 degrees centigrade.After the experiment, the thermometer is removed, placed in the asbestos net make its natural cooling to room temperatu
23、re, using waste paper to wipe bath, and then rinse with water. If the thermometer is removed from the hot bath immediately after washing, thermometer will by sudden rupture. Bath liquid cooling and then fell back to the bottle.5. calibration of thermometerWhen the melting point is measured by the ab
24、ove method, there is a certain deviation between the melting point readings of the thermometer and the true melting point. This may be due to the error of the thermometer. For example, the capillary hole in a general thermometer is not necessarily very uniform, and sometimes the calibration is not v
25、ery accurate. Secondly, there are two kinds of thermometer, full immersion and semi immersion. Full immersion scale thermometers are evenly heated in the mercury thermometer line under the condition of it, and the heating in measuring the melting point of only part of the mercury line, thus exposing
26、 the mercury line temperature is of course all heating is low. In addition, after long-term use of thermometer, glass may also occur volume deformation, so that the calibration is not allowed. In order to correct the thermometer, a standard thermometer can be used, and the melting point of pure orga
27、nic compounds is usually used as a standard for correction. The error can be removed by correcting the thermometer by this method. The correction as long as the choice of a number of pure compounds of known point as the standard, determination of their melting point, to observe the melting point and
28、 melting point known as abscissa, the difference of the longitudinal coordinate, drawing curves, at any temperature readings can be read directly from the curve.The melting point of a standard sample is as follows, and can be chosen when calibrated.Melting point (temperature) of sample, melting poin
29、t (DEG C)Water ice 0 urea 132Alpha naphthylamine 503, 5 - two nitrobenzo 204205Two aniline, 53, two, acetophenone two, 95Two chlorobenzene, 53 alpha naphthol 96Benzoic acid, phenyl ester 70, two phenyl hydroxy acetic acid 150Naphthalene 80 salicylic acid 159Two nitrobenzene, 90 anthracene, 216114 ph
30、enolphthalein acetanilide 215Benzoic acid 122 anthraquinone 286Adipic acid 132The best measure zero with a mixture of distilled water and pure water, distilled water 20ml placed in a 15X2.5cm tube, the tube immersed in ice cold distilled water bath to the part of the ice, with a glass rod to stir th
31、e ice water mixture will be removed from the ice bath tube, then the temperature gauge is inserted into the ice the water, gently stir the mixture, after constant temperature readings (23min).Thinking question1. what is the melting point? What is the melting process?2. what is the melting process of
32、 pure and impure materials?3. what problems should be paid attention to in capillary loading sample?Why should the 4. Sarkozy nozzle of the rubber plug slot?5. how high is the sample height in the capillary?6. when measuring the melting point, why should a small fire heating?7. if the sample tube of
33、 the first test can be used for second melting point measurements, why?8. what will happen if you encounter the following melting point?(1) the melting point tube is not clean.(2) the wall of melting point tube is too thick.(3) the sample is not carefully worked out.(4) heating too fast.Operation po
34、ints and instructionsThe main factors affecting the melting point of capillary method and the measures have been discussed:1, melting point tube itself should be clean, the pipe wall can not be too thick, sealing should be uniform. The problem is easy for beginners, sealing end bending and sealing e
35、nd wall is too thick, so in capillary sealing, is heated in the flame when trying to make capillary close to the vertical direction, the flame temperature is not too high, the best use of alcohol lamp, intermittent heating, sealing should be smooth, with no leakage principle.2, the sample must be dr
36、y, and to grind into fine powder, to the capillary inside the sample, must repeatedly impact ramming, outside the tube sample should be wiped with toilet paper.3. The capillary is attached to the thermometer by a rubber band, and the sample part is in the same horizontal position as the thermometer
37、and mercury bulb. The mercury bulb at the center of both sides of the B tube is also located at the same time.4, heating rate should not be too fast, especially when the temperature will be close to the melting point of the sample, the heating rate can not be faster. Generally, when the speed can be
38、 slightly warming up faster (5 C / min) but close to the melting temperature, heating speed is slower (1 - 2 C / min), to determine the melting point of the unknown, the first time can quickly heat up, determination about melting point compounds.5, the melting temperature range (melting point, melti
39、ng point and melting range) of the observation and recording, observation, sample (step down) indicating atrophy of the signal is not melting, the melting began to see the first drop of liquid, write down the temperature, to put all the complete disappearance of a crystal when the transparent liquid
40、 temperature, the two temperature is the melting point of the sample range.6, the melting point of the determination of at least two times repeated data, each determination must be a new melting point tubes, new samples. For second determinations, wait until the bath temperature is about 30 degrees
41、Celsius below the melting point.7, the use of sulfuric acid bath heating (heating medium) to be especially careful, cannot let the organic with concentrated sulfuric acid, otherwise the solution darkens, the melting point to observe. If this happens, add a small amount of potassium nitrate crystals
42、to heat them to make them discolored. Using concentrated sulfuric acid bath, suitable for measuring the melting point of 220 degrees below the sample. Samples are available to measure other bath liquid at the melting point above 220 DEG C. See Lan Da, Fudan book P431.Thinking question1, when measuri
43、ng the melting point, what will happen if the following conditions occur?(1) the wall of melting point tube is too thick.(2) the bottom of the melting point tube is not completely closed, and there is a pinhole.(3) the melting point pipe is not clean.(4) the sample is not completely dry or contains
44、impurities.(5) the sample is not finely worked or not tightly packed.(6) heating too fast.Answer: (1) the tube wall is too thick, the sample is not heated evenly, the melting point is inaccurate, the melting point data is easy to be high, and the melting process is large.(2) the bottom of the meltin
45、g point tube is not completely closed. There is a pinhole. The air will enter the person. When heated, bubbles can be seen to run out of the solution. Then the solution enters into the human body. The melting of the crystals will soon melt, and the measurement will be inaccurate.(3) the melting poin
46、t tube is not clean, equal to the impurity in the sample, so that the melting point is lower and the melting range is increased.(4) the sample is not completely dry, there are water and other solvents, heating, solvent gasification, so that the sample loose and melting, but also the melting point da
47、ta is low, the melting process increases. Samples containing impurities, the situation is the same.(5) the sample research not fine and pretend not to close, which contain voids filled with air, and the air thermal conductivity of a small heat slowly, will make the measured data of high melting poin
48、t melting process.(6) heating too fast and heating up fast will lead to high melting point data and large melting process, so heating can not be too fast.This is to ensure that there is sufficient time for the heat to be transferred from the tube to the tube to melt the solid. On the other hand, because the observer cannot observe both the degree of the thermometer and the change of the sample at the same time, only the slow heating can make the error smaller.2, can you use the first time to test the melting point when the organic compounds have been fused for second times? Wh