表常见固体有机化合物的熔点（Tablemelting points of common solid organic compounds）

1、表11常见固体有机化合物的熔点（Table 11 melting points of common solid organic compounds）Experiment 1 Determination of melting point of organic matterMelting point (melting, point) means the temperature at which a solid phase coexists with a liquid at equilibrium at atmospheric pressure at 1. According to this def

2、inition, the actual measurement, first heating amount of solid powder sample in capillary, observing the specimen from the initial melting temperature range to complete liquefaction. Thus, the resulting melting point is called the point melting (capillary). The melting point known in the general org

3、anic chemistry literature is the melting point of such a capillary.The melting point is important one of the physical properties of solid material, and can be used for detection and identification of the purity of the compounds. When solids contain impurities, they reduce the melting point and incre

4、ase the range of melting, i.e., the temperature range from the initial melting to the complete liquefaction. The determination of melting point is one of the basic operations in organic chemistry experiment.The melting point of commonly occurring solid organic compounds is shown in table 1.1.Table 1

5、.1 melting points of common solid organic compoundsCompound melting point (DEG C)Benzoic acid benzoic acid 122.4Urea urea 132.7Cholesterol cholesterol 148.5Salicylic acid 157159 salicylic acid(from The, Merck, index, 11th.ed)A device that measures the melting point usually has the following conditio

6、ns:(1) a convenient heat source is needed; a Bunsen burner or an electric heater is generally used.(2) the heat medium used shall be stable during heating so as to control the rise or fall of the sample temperature. Liquids with high thermal stability and high boiling point are often used, such as s

7、ilicone oil, glycerin, or salad oil, so that the heat is dispersed evenly without causing too much temperature change.(3) the temperature around the sample should be uniform so that the sample temperature is consistent with the measured temperature. This is usually done in agitators or convection.(4

8、) a temperature measuring device is required, usually with a thermometer, and the lower part of the thermometer should be as close as possible to the sample.If a solid organic compound is very close to pure, its melting range will be very narrow, about 0.5 1 degrees centigrade. But if impurities are

9、 present, the melting point is lowered and the range is increased. Therefore, the determination of melting point is not only a useful method for the identification of substances, but also the melting point is a basis for judging purity. Assume that a compound B and compound A, the melting point of t

10、he same, but is still unable to confirm whether the same kind of desirable compounds, a small amount of B and A mixed, the mixture of the determination of melting point; if the melting point of the same as A, B and A for the same kind of compounds; if the melting point in A, you can that B and A are

11、 not the same kind of compounds.equipmentEach groupHob1Iron clamp2Bunsen burner1A mortar and pestle1Melting point determination tube1Capillary (0.10 0.15 cm caliber, 7 cm long)5Glass tubes (0.8, x, 60, CM)1Spatula1Thermometer (0 200 degrees Celsius)1Cork (used with thermometer)1A rubber ring (cut of

12、f one end of the rubber tube)1ReagentEach groupBenzoic acid 0.05 grams0.05 grams of salicylic acidSilicone oil 100 ml.Experimental procedurePart 1: subject experimentsI. before melting point determinationIllustration and illustrationPreparation of capillary tubes for determination of 1. melting poin

13、tBy the end of the lamp heating capillary, melted into small beads shaped closed.When heating the capillary, it should rotate the capillary at any time so that it can be heated evenly without bending.2. fill in the sample to be tested(1) grind the test sample into small powder, pour it over a clean

14、sheet of white paper and pile it up.(1)(2) the inverted capillary, the opening is inserted in the powder sample, the sample into the tube, then the capillary upright (sealing end below). According to figure 1.1, the capillary into the glass tube, the bottom end of the collision by desktop, gravity a

15、nd inertia, the sample powder accumulated on the bottom of the capillary.(3) repeat (2) steps to the specimen height of about 2 4 mm; each specimen is filled with 3 capillary tubes.Figure 1.1 gravity loading testSampleAssembly of 3. melting point apparatus(1)(1) in the determination of melting point

16、 into the silicone oil pipe, the oil is not too high, and the iron clamp is fixed on the rack.(if it is already installed, it does not need to be repeated)(1)(2) the capillary of the filled sample is fixed to the thermometer with a rubber band, so that the specimen is located right next to the mercu

17、ry bulb of the thermometer.(1)(3) after the cork is drilled, cut a small gap with the knife, as shown in figure 1.2.Fig. 1.2 sectional drawing of cork(1)(4) a thermometer with a capillary which has been fixed to be tested is passed into the cork, and then the cork is stopped at the point of determin

18、ation of the melting point.(1)(5) adjust the thermometer and melting point to determine the distance between the tubes, so that the rubber ring is located on the oil surface, do not make it immersed in the oil, as shown in Figure 1.3, so as to avoid heating, rubber softening and lose elasticity.Fig.

19、 1.3 determination of temperature and temperature of melting pointDistance relation between degreesnote to operate this experiment, the melting point can be replaced by the following simple melting point apparatus without the determination of the melting point of Fig. 1-3.A. placed a 250 mL beaker i

20、n the hot iron net, built in about 2 / 3 of the silicone oil, and other fixed.B. take a cork and cut a small notch through the hole so that it can fix the thermometer and clearly observe the temperature scale.C. clamps the cork and the thermometer with the iron clamp, and adjusts the thermometer hei

21、ght, causes the bottom end to be about 3 cm from the beaker bottom.D. will be about 35 cm long glass rod, made in Figure 1.4 in a beaker, stir bar, upper and lower mixing silicone oil evenly heated.Fig. 1.4 simple melting point measuring deviceTwo. Determination of melting pointOne1. heating the mel

22、ting point tube directly with Bunsen burner, as shown in figure 1.5.The 2. is heated to the temperature lower than the melting point of about 15 20 degrees around the reference value, adjust the size of the flame, the temperature rise of the degree is no more than 2 per minute to 3 DEG C; melting po

23、int to lower than the reference value of 2 4 DEG C, then slow down the per minute rise of 1 degrees Celsius or more slowly.Fig. 1.5 melting point measuring device3. careful observation in the capillary reagent change and the change process of the thermometer; the phenomenon, as shown in figure 1.6.T

24、hree. Sample to be tested: benzoic acid (122.4 DEG C)The temperature at which the sample began to soften and the temperature at which all the solid specimens melted into liquid were recorded. The two temperature is called the melting point or melting point test.Figure 1.6 before the melting point of

25、 the compoundPost phenomenon change chartThe second part: extended experimentThe method of determining the melting point of organic compounds has been understood by the operation of the subject experiments. The determination of the melting point of an unknown substance will now be made to deduce the

26、 kinds of compounds contained in the unknown.To obtain the unknown from teachers, design the operation steps, conduct the melting point test, and then refer to Table 1.1 the melting point of common solid organic compounds for further inference and verification.The unknown for pure substance or mixtu

27、re? How to judge?If for a pure substance, which should be listed as the compound in the table? If it is a mixture, which two compounds should be included?The experimental data obtained with reference to other groups of students, we can deduce what conclusions?Experimental report on the determination

28、 of organic matter melting pointDate of experiment, date, dateClass numberFull nameName of the same classExperimental purposePart 1: subject experimentsExperimental records and resultsDetermination of melting point of benzoic acidExperiment timesThe temperature at which the melting beginsThe melting point (DEG C) of a solidIIIIIIProblems and discussion1. how important is it to determine the melting point?2. why does t