Chlorobenzene And Bromobenzene

The boiling points of three mixtures of chlorobenzene and bromobenzene were determined in this way,1 and the theoretical vapour pressures at these temperatures were then calculated. The results are given in Table 4.

Table 4

Molecular percentage of

C6H5Br.

Observed boiling point.

Vapour pressures at t°.

Actual pressure,

P1.

Chlorobenzene And Bromobenzene 29

PA-C6H5Br.

C6H5CI.

P.

Mixture

(calculated).

2501

136.75°

452.85

862.95

760.4

760.0

-0.4

50.00

14216

526.25

992.30

759.3

7600

+ 0.7

73.64

14816

618.40

115300

759.3

760.0

+ 0.7

Mean

759.7

Mean

+ 0.3

The differences are within the limits of experimental error.

The critical pressures of chlorobenzene and bromobenzene are equal, or nearly so,2 and it has been found that, when the two liquids are mixed in equimolecular proportions, there is no perceptible alteration of temperature or of volume, and it may therefore be concluded that

Chlorobenzene And Bromobenzene 30

The conditions specified by Van der Waals are therefore fulfilled, and in this case, at any rate, the formula gives the vapour pressures accurately.

Chlorobenzene And Bromobenzene 31

Table 5

Substance.

Critical pressure.

Chlorobenzene And Bromobenzene 32

Ethyl acetate .... Ethyl propionate ....

38.00 atm. 3317 „ }

4.83

Toluene ..... Ethyl benzene ....

41.6* „ 38.1* „ }

3.5

n-Hexane . . . . .

n-Octane .....

29.62 „ 24.64 „ }

4.98

Toluene ..... Benzene .....

41.6* „ 50.1* „ }

8.5

Benzene . . . . . Carbon tetrachloride . . . . .

47.88 „ 44.97 „ }

2.91

Methyl alcohol .... Ethyl alcohol ....

78.63 „ 62.96 „ }

15.67

* As the critical pressures of both toluene and ethyl benzene have been determined by Altschul,3 it seems best to give his value for benzene in the comparison with toluene.

1 Young, "The Vapour Pressures and Boiling Points of Mixed Liquids, Part I.," Trans. Chem. Soc, 1902, 81, 768.

2 Young, " On the Vapour Pressures and Specific Volumes of similar Compounds of Elements in Relation to the Position of those Elements in the Periodic Table," Trans. Chem. Soc, 1889, 55, 486.

3 Altschul, "On the Critical Constants of some Organic Compounds," Zeitschr. physik. Chem., 1893, 11, 577.

Other Mixtures Of Closely Related Compounds

It does not follow, however, that it is only when the critical pressures are equal that the formula is applicable, and it will be seen from Table 6 that the deviations may be exceedingly small when the liquids are closely related but their critical pressures (Table 5) are widely different.1

Table 6

Mixture.

Molecular percent-age of

A=M.

Pressures.

Change on mixing in equimolecular proportions.

Actual P'.

Calculated P.

A P'-P.

Volume per cent.

Tempera-ture.

A. Ethyl propionate

B. Ethyl acetate . }

25.01 50.00 74.62

mm.

760 "

"

mm. 756.5 755.7 754.6

mm. + 3.5 + 4.3 + 5.4

+ 0.015

* -0.02°

Mean

755.6

+ 4.4

A. Ethyl benzene .

B. Toluene . . }

25.02 49.97 75.00

760 "

"

762.8 763.5 765.5

- 2.8

- 3.5

- 5.5

-0.034

+ 0.05

Mean

763.9

- 3 9

A. n-Octane . .

B. n-Hexane . . }

23.31

50.00 74.99

760

" "

752.0 760.2 781.6

+ 8.0 - 0.2 - 21.6

-0.053

+ 0.06

Mean

764.6

- 4.6

A. Toluene . .

B. Benzene . . }

24.94 50.00 72.46

760

"

"

760.6 762.9 764.5

- 0.6

- 2.9

- 4.5

+ 0.161

-0.45

Mean

762 7

- 2.7

A. Ethyl alcohol .

B. Methyl alcohol . }

50.13

760

759.4

+ 0.6

+ 0.004

-010

* The temperature changes given here are merely comparative ; they were observed by mixing together, in a round-bottomed flask, equimolecular quantities (22 c.c. in all) of the two substances. The temperature given is the difference between that of the mixture and the mean of those of the components, which never differed by more than 0.2°. The alterations of temperature show the direction and give a rough indication of the magnitude of the corresponding heat changes.