Idea Transcript
THE BOILING POINTS, COMPOSITIONS, AND DENSITIES OF THE AZEOTROPES OF DEUTEROCHLORIC ACID
by WOODLAND EUSTACE ERLEBACH
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE in the Department of CHEMISTRY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE
Members of the Department of CHEMISTRY THE UNIVERSITY OF BRITISH COLUMBIA April, 19S3
ABSTRACT
The b o i l i n g points, densities, and compositions of constant b o i l i n g deuterochloric acid have been determined at pressures between 200 and 1000 mm.
The b o i l i n g points, determined with apparatus
s i m i l a r to that used f o r the determination of the b o i l i n g points of hydrochloric acid, were found to d i f f e r to a very small degree from those of hydrochloric acid.
The compositions were found to vary
from 1 9 . 6 6 1 percent deuterium chloride at 202.5 mm to 17.1U6 percent at 998.h mm;
about 2 . 5 and 2 . 2 percent lower than hydrochloric acid
prepared at those pressures.
The densities were found to vary from
1.2003U gms per ml at 202.5 mm to 1.1877U gms per ml at 998.h mm. The relationship between b o i l i n g point and percent composition and :
between density and percent composition were found to be c l o s e l y l i n e a r over the range investigated. These results were correlated and compared with the data on hydrochloric acid.
The d i f f i c u l t i e s i n explaining the difference
i n the properties of the two azeotropes i s pointed out, and the application of t h e o r e t i c a l relationships i s discussed.
ii
TABLE OF CONTENTS Page 1
ABSTRACT
:2
INTRODUCTION A.
H i s t o r i c a l Basis
B.3
Theory
2 lh
1.
Vapor-Liquid Equilibrium
U
2.
Thermodynamic Relationships i n Azeotropism
8
Equations of Reddich and Schutz
(b)
Equations of Coulson and Herington
12
(c)
Equations of Kireev
17
(d)
Equations of Carlson and Colburn
18
(e)
Comparison of Equations
19
EXPERIMENTAL METHODS AND RESULTS A.
B.
8
(a)
21
Apparatus
21
1.
Preparation Apparatus
21
'2.
Dry A i r D i s t r i b u t o r
22
3.
D i s t i l l a t i o n Unit
22
U.
Pressure Apparatus
23
5.
Pycnometric Equipment
2k
6.
Ebulliometric Apparatus
2h
7.
A n a l y t i c a l Equipment
27
8.
Dry Box
27
,
Procedure
27
1.
Preparation of the Acid
27
2.
D i s t i l l a t i o n of the Azeotrope
29
3.
Determination of Density
31
C.
h.
Determination of Boiling Point
33
5.
Determination of Composition
3h
Results
36
1.
Preparation
36
2.
Azeotropic Data and Empirical Correlations
37
3.
Calibration of Resistance Thermometer
1|1
h.
Test Determinations on Hydrochloric Acid
U2
5.
Isotopic Purity of Deuterium Oxide
k3
DISCUSSION A.
B.
Precision and Accuracy
hh
1.
Isotopic Purity of the Azeotrope
hh
2.
Pycnomet ry
1;7
3.
Manometry
U8
h.
Ebulliometry
50
5.
Composition
5H
Comparison of Properties
55
Linearity of Correlations
58
Applications of Data
59
• C. D.
hh
REFERENCES
6li
APPENDIX
66
I '
Illustrations
66
Fig. 1
66
Preparation Apparatus
Fig. 2A Distillation and B oiling Point Apparatus 2B Pycnometer Fig. 3 Fig. h
Relationship between boiling point and pressure •
68
Relationship between boiling point and percent composition
69
Fig. 5 Relationship between pressure and percent composition
70
Fig. 6 Relationship between density and percent composition
71
Fig. 7 Bifference between observed and calculated boiling points
72
Fig. 8 Relationship between logarithm of pressure and reciprocal boiling point
73
Fig. 9 Determination of mean distillation pressure
7h
Fig. 10 Temperature and pressure at which the azeotrope disappears II
Azeotropic Data
III
Calculations
75 76
•
78
1.
Composition
78
2.
Density
80
3.
Correlation of boiling point and composition Relation between mole fraction and percent composition Calculation of mean pressure and its mean
U. 5.
deviation
81 83 8U
IV
Barometric Corrections
85
V
Calibration of Weights
85
VI
Notation
87
2.
INTRODUCTION
A.
Historical Basis John Dalton, in 1832, discovered that water and hydrogen
chloride of a specific composition had a constant boiling point. This boiling point was found to be so constant that an earlier investigator ' (1) assumed that the mixture formed a compound.
Two
years later, in i860, Roscoe and Dittmar (33) showed that the composition of this mixture varied v/ith pressure.
Almost senenty
years later Briggs (5) described a method of using this property to detect and separate constant boiling mixtures.
He d i s t i l l e d a
mixture of hydrogen chloride and water i n a fractionating; column;.at 1
an arbitrary pressure.
After the bottoms composition became constant,
he refractionated the residue at another pressure and examined the f i n a l residue. He found that the f i r s t fractionation increased the hydrogen chloride content of the residue, and the second fractionation reduced i t . Aside from the fact that hydrochloric acid was one of the f i r s t azeotropes discovered, i t s use as a volumetric standard has prompted a thorough investigation of i t s composition when the acid is d i s t i l l e d at approximately atmospheric pressure.
After the
suggestion by Hulett and Bonner in 1909 (17) that because of i t s definite composition the constant boiling azeotrope would provide a good volumetric standard, a number of investigators published data on the azeotrope.
Foulk and Hollingsworth (13) compared the data
of Hulett and Bonner (17), Morey (28), and Hendrixon (16), with
t h e i r own on the composition of the azeotrope prepared at 750 pressure.
mm
They found that a f t e r appropriate corrections had been
applied to the e a r l i e r data agreement i n composition was found to within 0 . 0 1 percent. Although constant b o i l i n g hydrochloric acid has d i s t i n c t advantages as a primary standard, Shaw (35)
observed that the use
of benzoic acid and sodium carbonate f o r t h i s purpose f a r exceeded the use of the azeotrope.
He assumed that the cause of the lack
of use l a y i n the uncertainty of the s t a b i l i t y of the acid.
To
investigate t h i s s t a b i l i t y Shaw kept samples of the a c i d i n w e l l stoppered bottles i n the dark f o r periods up to three years.
During
that time the concentration d i d not change by more than 5 parts i n 10,000. Bonner, who with Hulett did some of the e a r l i e s t work on the azeotrope, extended the data by determining p r e c i s e l y the b o i l i n g points, densities, and compositions of the azeotropes prepared at various pressures between 50 and 1220 mm.
This work
was c a r r i e d out i n conjunction with Titus (3), Branting (2), Wallace
(H).
The b o i l i n g points of the azeotropes as determined
Bonner and Wallace were l a t e r checked by Cadbury (7) found within
and
±
and agreement
0.05°C.
The determination, i n 193U,
of the vapour pressure of
deuterium chloride and the comparison of t h i s data with that of hydrogen chloride by Lev/is, MacDonald, and Schutz (22), -suggests the i n t e r e s t which might attend the comparison of the properties of deuterochloric acid and hydrochloric a c i d .
by
a.
B i.
Theory
(l)
tapor-Liquid Equilibrium In the study of liquid mixtures i t is customary to define
an ideal mixture as one that obeys Raoult's Lgw over the whole range of concentration.
Raoult's Law states that the partial vapor
pressure of a constituent i s proportional to i t s mole fraction in the liquid at a l l concentrations.
Applied to a constituent A this
may be expressed mathematically as P
A
PA A >
=
W
X
where p^ is the partial pressure, p^ is the vapor pressure of the pure liquid, and x^ is the mole fraction.
Any binary solution such
that the relationship between total vapor pressure and composition is not linear may be defined as non-ideal. These relationships for non-ideal binary solutions are given by the Duhem-Margules equation (11,
2a) . This was
first
derived by Gibbs and later, independently, by Duhem, Margules, and Lehfeldt.
It may be derived from partial free energy relationships
to give the following equation: din p
A
din x^
_ din p
^
B
din Xg
This equation assumes only that the vapors of the two components behave ideally.
It makes no assumption regarding the ideality or
otherwise of the liquid mixture.
The validity of this equation
was studied by Zavaritzkii (a2) for water and hydrogen chloride solutions from 0 to 30 percent hydrogen chloride and found to be correct.
Rosanoff (32) states that the equation is absolutely
5.
general and, should hold for a l l actual vapors up to their criticalpoints. The Duhem-Margules equation may be integrated to the form: o X «E Bx n , ° «x2 , .
P =P A
A
A
and p = P B X e A B
b
where