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Solubility of chlorine in aqueous hydrochloric acid solutions

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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. (c) 2004 Elsevier B.V. All rights reserved.
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Journal of Hazardous Materials A119 (2005) 13–18
Solubility of chlorine in aqueous hydrochloric acid solutions
Mahir Alkana,M¨
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
Abstract
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
1. Introduction
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) [1]. 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 [2].
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: mcopur@atauni.edu.tr (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 [3].
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 [4].
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 [1]:
Cl2+H2OH++Cl+HOCl (1)
This reaction is reversible. It was found that the forward
reaction is first order [5]. The rate of this reaction was stud-
ied by Lifthitz and Perlmutter-Haymen [6], Shilov and Solo-
dushenkov [7] and Brian et al. [8]. The equilibrium constant
0304-3894/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jhazmat.2004.11.001
14 M. Alkan et al. / Journal of Hazardous Materials A119 (2005) 13–18
for Eq. (1). is given by:
K=[H+][Cl][HOCl]
[Cl2](2)
This means that as HCl concentration increases, the equi-
librium shifts to left and Cl2solubility decreases [5].
Leaist [9] 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
partial pressure.
On the other hand, Islam et al. [10], 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
Henry’s Law.
Awakura et al. [11] 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 L1, 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. [12], 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.
[14] investigated the dissolution of chalcopyrite containing
pyrite in Cl2saturated water and they gave the dissolution
reactions as
2FeS2(s) +15Cl2(aq) +16H2O
2FeCl3(aq) +4H2SO4(aq) +24HCl(aq) (4)
2CuFeS2(s) +14Cl2(aq) +16H2O2FeCl3(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
food products.
However,excessivedemandofindustrytosodiumhydrox-
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.
2. Experimental
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 [18]. 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
TheeffectoftheconcentrationofHClonthesolubilitywas
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[19]. 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
solutions.
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
equation[19]:
Cl2+ClCl3(6)
Results from Awakura et al. [11] also confirm this sight.
But,theseauthors found outa minimum point at0.2 M of HCl
concentration,graphically.Inthepresentstudy,thisminimum
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 ×108exp 2927
T10.73[HCl]3/2
+63.55[HCl] 89.41[HCl]1/2+92.02(7)
where Cis the solubility in water and HCl solutions in
molL1,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
good.
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).
Table 1
Thermodynamic characteristics of dissolution of Cl2in hydrochloric acid
solutions
Concentration of HCl (mol L1)H(kJmol1)S(J mol1K1)
019.75 88.02
0.122.45 98.66
0.327.45 116.29
0.529.73 125.55
1.027.48 117.21
2.028.35 119.11
3.027.62 115.81
5.026.44 110.42
7.026.31 108.63
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 [20] by plottingln Cversus
1/Tin terms of the following equation (Fig. 3a and b):
lnC=−H/RT +S/R(8)
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 [21].
4. Conclusions
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
metallurgical and electrowinning processes in future.
References
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[3] http://www.doulton.ca/chlorine.html.
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... It remains constant for the next two hours. It has been established that an increase in the duration of the experiment from 0.5 to 3 h leads to additional heating of the electrolyte from 52 °С to 76 °С, which causes a decrease in the solubility of chlorine in the hydrochloric acid electrolyte solution [48]. It should be noted that these data are in good agreement with the results presented in Figure 13b, namely that active dissolution of gold begins 30 min after the beginning of the experiment. ...
... It remains constant for the next two hours. It has been established that an increase in the duration of the experiment from 0.5 to 3 h leads to additional heating of the electrolyte from 52 • C to 76 • C, which causes a decrease in the solubility of chlorine in the hydrochloric acid electrolyte solution [48]. It should be noted that these data are in good agreement with the results presented in Figure 13b, namely that active dissolution of gold begins 30 min after the beginning of the experiment. ...
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... It remains constant for the next two hours. It has been established that an increase in the duration of the experiment from 0.5 to 3 h leads to additional heating of the electrolyte from 52 °С to 76 °С, which causes a decrease in the solubility of chlorine in the hydrochloric acid electrolyte solution [48]. It should be noted that these data are in good agreement with the results presented in Figure 13b, namely that active dissolution of gold begins 30 min after the beginning of the experiment. ...
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An empirical equation is proposed to describe the solubility vs pressure relation for some reactive gases. The systems under consideration are ammonia/water, sulfur dioxide/water, chlorine/water, and hydrogen chloride/water. It is assumed that the reactive gases are dissolved in water by two mechanisms: one described by Henry's law and the other by a Langmuir type equation. Out of the four systems only hydrogen chloride showed no Henry's type of sorption, and a threshold concentration term was added to validate the model. The proposed equation fits well to the solubility/pressure data from the literature. A possible variation in the:values of the empirical coefficients with the change in the water chemistry (pH, ionic strength) is also discussed.
Article
The rate of absorption of chlorine into water in a short wetted-wall column is measured at 15, 25, and 40°C. The results agree well with previously published penetration theory predictions when values of 8.5, 15.4 and 46 (sec)−1 are chosen for the chlorine hydrolysis rate constant at 15, 25, and 40°C, respectively. These values show good agreement on an Arrhenius plot with published kinetic measurements at lower temperatures.RésuméLes auteurs mesurent la vitesse d'absorption du chlore dans l'eau dans les courtes colonnes à parois mouillées aux températures de 15, 25 et 40°C. Les résultats sont en excellent accord avec les productions antérieures obtenues à partir de la théorie classique de la “pénétration”, choisissant pour valeur de la constante de vitesse de l'hydrolyse du chlore respectivement 8,5-15,4 et 46 sec−1 à 15, 25 et 40° C.Ces valeurs sont en accord avec le diagramme d'Arrhenius et les mesures de cinétique à basse température.ZusammenfassungIn einer kurzen Naβwandkolonne wird die Absorptionsgeschwindigkeit von Chlor in Wasser bei 15, 25 und 40°C gemessen. Die so erhaltenen Ergebnisse stimmen mit früheren Voraussagen aufgrund der Penetrationstheorie überein, wenn die Hydrolysenkonstante des Chlors bei diesen Temperaturen zu 8,5 15,4 und 46 sec−1 angenommen wird; die Übereinstimmung gilt auch für den Vergleich mit früher veröffentlichten Meβdaten bei tieferen Temperaturen.
Book
Fundamentals of Analytical Chemistry is divided into three roughly equal parts. The first 14 chapters cover classical methods of analysis, including titrimetry and gravimetry as well as solution equilibria and statistical analysis. The next 11 chapters address electroanalytical, optical, and chromatographic methods of analysis. The remainder of the text is devoted to discussions of sample manipulation and pretreatment, good laboratory practices, and detailed directions for performing examples of 17 different types of classical and instrumental analyses. Like its predecessors, this fifth edition provides comprehensive coverage of classical analytical methods and the major instrumental ones in a literary style that is clear, straightforward, and readable. New terms are carefully defined as they are introduced, and each term is italicized for emphasis and for ease of relocation by the student who may forget its meaning. The chapters on analyses of real-world samples, on avoiding interferences, and on techniques for sample preparation should prove especially useful for the practicing chemist.
Article
The rate of absorption of chlorine from chlorine-nitrogen mixtures into solutions of ferrous chloride in 0.203 N aqueous hydrochloric acid was studied in a short wetted-wall column. Dimensional analysis and the film and penetration theories were used to infer, from the absorption rate data, that the chemical reaction between chlorine and the ferrous ion is second order. The absorption-rate results for experiments with a dilute gas phase agreed with theoretical predictions for absorption accompanied by a second order reaction with a reaction rate constant of 188 liters/(g. mole) (sec.). The results for experiments with pure chlorine gas deviated from the rest of the results, and they did not agree with the theoretical equations. It was shown that the assumption of a three-step mechanism for the chemical reaction, including the formation of a complex ion and the decompositon of this complex ion, explains, at least qualitatively, the deviations observed for the pure chlorine gas runs.