Journal of Hazardous Materials A119 (2005) 13–18
Solubility of chlorine in aqueous hydrochloric acid solutions
unir Oktayb, M. Muhtar Kocakerimc, Mehmet C¸opurc,∗
aDepartment of Chemistry, Faculty of Science and Literature, Balikesir University, Balikesir, Turkey
bDepartment of Chemistry, K.K. Faculty of Education, Atat¨urk University, Erzurum, Turkey
cChemical Engineering Department, Engineering Faculty, Atat¨urk University, Erzurum, Turkey
Received 23 April 2004; received in revised form 2 November 2004; accepted 6 November 2004
Available online 15 December 2004
The solubility of chlorine in aqueous hydrochloric acid solutions was studied. The effects of HCl concentration and temperature on the
solubility were evaluated, and the thermodynamic parameters of the dissolution were calculated. It was found that the solubility isotherms had
a minimum at about 0.5 M HCl concentration at all the temperatures studied and that solubility decreased with the increase of temperature at
all the HCl concentration range investigated.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Solubility; Chlorine; Hydrochloric acid; Thermodynamic parameters
Chlorine is an element of the halogen family, but it is
never found uncombined in nature. It is estimated to ac-
count for 0.15 percent of the earth’s crust in the form of
soluble chlorides such as common salt (NaCl), carnallite
(KMgCl3·6H2O) and sylvinite (KCl) . Chlorine gas is
especially produced as a by-product in the electrolysis of
sodium chloride in the chloroalkali industry. Generally, most
producers operate their plants to make chlorine since it is
hard to store and is used to product derivatives such ethy-
lene dichloride, phosgene and epichlorhydrine. Caustic soda
is generally sold on the merchant market and consumed in a
myriad of uses. Little chlorine is traded among countries, but
a considerable amount of caustic soda is traded, especially in
aqueous form .
Chlorine is a very effective disinfectant and has been used
in drinking water supplies for nearly 100 years. Risks for
certain types of cancer are now being correlated to the use
of chlorinated drinking water. Suspected carcinogens make
∗Corresponding author. Tel.: +90 442 2314573; fax: +90 442 2361129.
E-mail address: firstname.lastname@example.org (M. C¸ opur).
the human body more vulnerable through repeated ingestion
and research indicates the incidents of cancer are 44% higher
among those using chlorinated water .
On the other hand, chlorine released to atmosphere causes
depletion of the ozone layer which absorbs most of the harm-
ful ultraviolet-B radiation from the sun. To prevent the de-
pletion of ozone shield, developed countries have made pro-
tocols and some international regulations have arranged. For
that reason, new and applicable uses must be found to con-
sume chlorine .
When chlorine gas is dissolved in water, it is rapidly hy-
drolysed and a special type of oxidation–reduction reaction
takes place. The chlorine molecule with the sum valence of
zero enters into the reaction known as disproportion reaction
with water as following :
This reaction is reversible. It was found that the forward
reaction is ﬁrst order . The rate of this reaction was stud-
ied by Lifthitz and Perlmutter-Haymen , Shilov and Solo-
dushenkov  and Brian et al. . The equilibrium constant
0304-3894/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
14 M. Alkan et al. / Journal of Hazardous Materials A119 (2005) 13–18
for Eq. (1). is given by:
This means that as HCl concentration increases, the equi-
librium shifts to left and Cl2solubility decreases .
Leaist  used solubility and diffusion data to describe
absorption of chlorine gas into water at 25 ◦C and 1 atm pres-
sure. The author stated that hydrochloric acid produced by
partial hydrolysis of molecular chlorine in according to Eq.
(2), diffuses rapidly into the bulk liquid and because the sur-
face of the absorbent is depleted in hydrochloric acid, the
solubility of chlorine in the interfacial liquid is signiﬁcantly
higher than the equilibrium solubility at the same chlorine
On the other hand, Islam et al. , made an attempt to
propose an empirical model describing the solubility versus
partial pressure relation over a wide range of concentrations
for some reactive gases, including chlorine. As a result, they
found out that the solubility of gas is the sum of two com-
ponents, one ﬁtting the Langmuir isotherm and other ﬁtting
Awakura et al.  investigating solubility of chlorine gas
in various chloride solutions at 298K found out that the sol-
ubility in aqueous HCl solutions decreases drastically with
increasing HCl concentrations up to 0.2mol L−1, and then,
it increases gradually with a further increase in HCl con-
centration. Also, the authors determined that the solubility of
chlorinegasdecreasessteadily with increasing MClx concen-
tration in aqueous HCl solutions containing MClx [M= Na,
K, Ca, Ba, Mg, Ni, Co, Zn, Fe(III)].
Gilliand et al. , on the other hand, measured rates of
absorption of Cl2into FeCl2solutions in a wetted-wall col-
umn. The overall reaction was
Cl2(g) +2Fe2+(aq) →2Fe3+(aq) +2Cl−(aq) (3)
Inusing chlorine diluted withnitrogen the absorption rates
agreedwellwithpredictions based on a second-orderreaction
between Cl2and Fe2+.
Recently, chlorine gas was used as a reactant in the disso-
lution of various ores in aqueous media [13–17].C¸olak et al.
 investigated the dissolution of chalcopyrite containing
pyrite in Cl2saturated water and they gave the dissolution
2FeS2(s) +15Cl2(aq) +16H2O
→2FeCl3(aq) +4H2SO4(aq) +24HCl(aq) (4)
2CuFeS2(s) +14Cl2(aq) +16H2O→2FeCl3(aq)
+2CuCl2(aq) +4H2SO4(aq) +24HCl(aq) (5)
Before the tremendous increase of the use of chlorine in
chemical industry, most chlorine was used in the textile in-
dustry for bleaching purposes. It is the most unusual and
versatile substance with more diverse uses than any other
chemical known—from rocket fuels to the manufacture of
ide increases inevitably the production of chlorine. This case
isrequired to ﬁnd new uses for chlorine gas. So, itwas though
that the data, which make possible to use chlorine gas espe-
cially in hydrometallurgy, could be obtained.
To consume chlorine gas more safely and more environ-
mentally friendly and to stabilize it, it is required to improve
industrially the applications such as in Eqs. (3) and (4) in
which HCl occurs. For this reason, a fundamental study was
undertaken to establish the solubility of chlorine gas in HCl
solutions and to predict the some thermodynamic data.
Theexperimentswere carried out at atmospheric pressure,
81.33kPa in Erzurum,Turkeybyusing a glass ﬂask equipped
with a gas inlet and outlet tubes and a magnetic stirrer. The
ﬂask was immersed in a constant temperature bath. The iodo-
metric titration method was used in determining the concen-
tration of Cl2in solution . The titrations were made until
thesame valueswas obtained in three or more subsequent de-
terminations at each temperature. The same procedure was
repeated at other temperatures and then for other solutions of
HCl.Thechlorinegas used was obtained from Koruma-Tarım
Corp., Turkey. Other chemicals were from Merck.
3. Result and discussion
The obtained experimental data showed that the concen-
trationof HCl and temperature affectedthe solubility of chlo-
rine in aqueous hydrochloric acid solutions (Figs. 1–3).
3.1. The effect of HCl concentration
investigated in the concentration range 0–7.0M. The results
obtained are shown graphically in Fig. 1.
As seen from this ﬁgure, each isotherm consists of two
different parts. In the ﬁrst region, the solubility of Cl2de-
creases with increasing HCl concentration from 0 to 0.5M.
It is known that the presence of any electrolyte causes the
reduction of the solubility of a gas in any solvent because the
amount of free solvent molecules decreases. Also this
means that at HCl concentrations lower than 0.5M, the sol-
ubility of chlorine ﬁts to Eq. (2) given by Brian. According
to this equation, as HCl concentration increases, the equi-
librium shifts to left and solubility decreases. On the other
hand, in the second region in which HCl concentration is
bigger than 0.5M, Eq. (2) is not valid and chlorine solubil-
ity increases by increasing HCl concentration. In this region,
M. Alkan et al. / Journal of Hazardous Materials A119 (2005) 13–18 15
Fig. 1. Dependence of solubility of Cl2on initial concentration of HCl.
Fig. 2. (a) The effect of temperature on the solubility of Cl2in aqueous HCl solutions. (b) The effect of temperature on the solubility of Cl2in aqueous HCl
16 M. Alkan et al. / Journal of Hazardous Materials A119 (2005) 13–18
Fig. 3. (a) ln Cvs. 1/Tplots of results obtained. (b) lnCvs. 1/Tplots of results obtained.
increase in the solubility is probably due to the formation of
complexion,Cl3−,in the medium,accordingto the following
Results from Awakura et al.  also conﬁrm this sight.
But,theseauthors found outa minimum point at0.2 M of HCl
was obtained in 0.5M of HCl concentration. This case was
attributed to the fact that solubility changes were very small
in 0.1–0.5M HCl concentration range and Awakura et al.
had studied at only one temperature. Because, in the present
investigation, solubility was studied at six various tempera-
tures and found out that the minimum point was 0.5M HCl
concentration for all the temperatures.
3.2. Modeling the solubility
Some semi-empirical models have been derived for solu-
bilities of gases in liquids. These models generally are non-
reactive gases and can not be applied to the system here,
especially second part of solubility isotherms.
For this, a new equation representing the dependence of
the solubility on the concentration of HCl and temperature
was derived by using PC as follows:
C=4.46 ×10−8exp 2927
where Cis the solubility in water and HCl solutions in
molL−1,Tthe temperature (K), [HCl] the HCl concen-
tration. To test the agreement between the experimental
conversion values and the values calculated from Eq (7),
a plot of the observed solubility values versus predicted
solubility values for 0–7M acid concentration range was
drawn in Fig. 4. The agreement between the experimen-
tal and calculated conversion values were found to be very
3.3. The effect of temperature
This effect was studied at the temperatures of 293, 303,
313, 323, 333 and 343K. As shown in Fig. 2a and b, the
M. Alkan et al. / Journal of Hazardous Materials A119 (2005) 13–18 17
Fig. 4. Agreement between observed solubility values and predicted solubility values from the Eq. (7).
Thermodynamic characteristics of dissolution of Cl2in hydrochloric acid
Concentration of HCl (mol L−1)H(kJmol−1)S(J mol−1K−1)
solubility of Cl2decreases as the temperature increases at all
the HCl concentrations studied.
3.4. Thermodynamic parameters
The thermodynamic parameters of the dissolution process
were also determined. The heat and entropy change of the so-
lutionwerecalculatedgraphically  by plottingln Cversus
1/Tin terms of the following equation (Fig. 3a and b):
The results obtained are summarized in Table 1. The anal-
ysis of thermodynamic parameters shows that the enthalpies
and entropies of Cl2dissolution in solution of HCl are lower
than those in water, indicating the formation of more highly
ordered structures in solution .
Investigation of the solubility of Cl2in HCl solutions
(0–7.0M) in the temperature range 293–343 K showed that
theCl2solubility isotherms had minimum inthe region 0.5M
HCl. The solubility of Cl2decreases with the increase of
temperature at all the HCl concentration range studied. The
thermodynamic parameters of Cl2dissolution in HCl solu-
tions were calculated and show evidence that enthalpies and
entropies of solubility of chlorine gas in HCl solutions are
lower than those in water.
These data will be useful in the use of chlorine gas in
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