Determination of Boiling Points

Determination of Boiling Point.—After the liquid has been placed in the distilling flask, the thermometer which is chosen to suit the substance, as in the determination of melting points, is fixed in the neck of the flask by means of a thin cork, so that the bulb of the thermometer is opposite the exit tube. 

The flask is then fixed to a Liebig or air condenser by means of a cork placed near to the neck of the flask. The condenser is attached to an 

Before heating is commenced, a small piece of unglazed porcelain or magnesite is introduced into the flask in order to prevent bumping  

When there is only a very small quantity of liquid available, two methods may be applied — 

A very small distilling flask, preferably pear-shaped, may be used. The sketch (Fig. 10) shows a very useful type of flask for this purpose. These flasks can be obtained of capacity down to 1 c.c. The hood prevents condensed liquid returning to the bulb. 

When reasonable amounts of liquid components are available ( 5 ml) the boiling point is readily determined by slowly distilling the material from a pear-shaped flask in an apparatus assembly shown in Fig. 2.98, and recording the temperature at which the bulk of the compound distils. Due attention should be paid to the experimental procedure which was discussed in detail in Section 2.24. 

For smaller quantities of liquid compounds (0.5-3.0ml) the material should be distilled in the apparatus assembly shown in Fig. 2.99. 

When only minute quantities of liquid are available, either of the two micromethods for the determination of the boiling point may be used. 

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Experimental Determination of Boiling-point. Unless only minute quantities of the liquid are available cj. p. 60), the boiling-point is usually determined by simple distillation. For this purpose, the apparatus shown in Fig. 2 is assembled. A distillation flask A of suitable size is fitted to a water-condenser B, the water supply of which is arranged as show-n. An adaptor C is sometimes fitted in turn to the condenser, so that the distillate... 

Determination of Boiling-points. The following alternative methods are recommended, (a) Draw one drop of the liquid into a capillary tube so that the drop is about i cm. from one end. 

Determination of boiling points. Distillation method (Fig. II, 12, 1) for carbon tetrachloride (25 nil. distillation flask and small water condenser), and SiwoloboflF s method (Fig. II, 12, 2) for carbon tetrachloride, aniline and nitrobenzene. Calibration curve for thermometer. Determination of b.p. of unknown liquid. 

Garcia, C.R. Determination of boiling points of pure organic liqnids, Ind. Eng. Chem. Anal Ed., 15(10) 648-649, 1943. 

Some plasticizer mixes require pretreatment, such as saponification, but in most instances chromatographic separations can be accomplished with the mix. In addition to the usual identification of substances by organochemical analysis, other methods now being used include color tests, physical tests (determinations of boiling point and refractive index), and infrared and ultraviolet spectroscopy. 

The various methods for the experimental determination of boiling point of a liquid by distillation are discussed in Section 2.24 for sample sizes ranging down to about 0.5 ml. If the liquid is shown by distillation to have a wide boiling range (10-30 °C), it will be necessary to subject it to fractional distillation, or to one of... 

Determination of Boiling-Point.—It is not usual to determine both the melting-point and the boiling-point of the same compound, for one of the two often comes outside of the range of ordinary laboratory operations. The melting-point is generally determined in the case of compounds that are solid at ordinary temperatures, and the boiling-point in the case of those that are liquid. 

Hydrogen bonding is most evident in the determination of boiling points of hydrogen containing molecules. Specifically, compare the boiling points of the hydrides of Groups IV, VI and VII... 

Fig. 13.Vin J. Apparatus for Determination of Boiling-points of Metals under Pressure...

Figure 2.24 Apparatus for small-scale determination of boiling point...

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