J. Chem. Thermodynamics 88 (2015) 78–84
Contents lists available at ScienceDirect
J. Chem. Thermodynamics
journal homepage: www.elsevier.com/locate/jct
Thermodynamic properties determination of aqueous mixtures of CaCl2
and Ca(NO3)2 by the potentiometric method at T = 298.15 ± 0.1 K
Amir Rahimzadeh, Mohammad A. Bagherinia ⇑
Department of Chemistry, Faculty of Science, Lahijan Branch, Islamic Azad University, Lahijan, Iran
a r t i c l e
i n f o
Article history:
Received 29 October 2014
Received in revised form 26 March 2015
Accepted 1 April 2015
Available online 23 April 2015
a b s t r a c t
The main goal of this work is to provide precise thermodynamic data about the ternary system
(CaCl2 + Ca(NO3)2 + H2O), which may allow modeling its behavior. The Pitzer ion interaction model and
Harned rule were used to illustrate the ternary electrolyte system. The activity coefficients were determined using a potentiometric method. The measurements were performed at T = 298.15 ± 0.1 K and at
total ionic strengths from (0.0010 to 5.0000) mol kg1. Different series of molal salt ratios were
mCaCl
Keywords:
Thermodynamic properties
CaCl2
Ca(NO3)2
Pitzer model
Potentiometric method
r ¼ mCaðNO 2Þ = 1.00, 2.50, 5.00, 10.00 and 15.00. The PVC based calcium ion-selective electrode (Ca2+-ISE),
3 2
and the Ag/AgCl electrode used in this work were prepared in our laboratory. The mixing Pitzer parameters (hClNO3 ; WCaClNO3 ) were determined for this system. Then these parameters were used to calculate
thermodynamic properties such as the osmotic coefficients (;), the activity coefficients of Ca(NO3)2 in
the mixture (cCaðNO3 Þ2 ) and the excess Gibbs free energy (GE). The experimental results showed that both
Pitzer model and Harned rule were suitable to be used satisfactorily to describe this system.
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
In recent years, there has been an increasing amount of work
investigating the thermodynamic properties of mixed aqueous
electrolyte solutions, particularly at high total ionic strengths
[1–4]. This is because in many fields including chemistry, chemical
engineering, biology, geology, atmospheric science, and food processing thermodynamic properties of mixed aqueous electrolytes
are important [5–7].
Free energy values, water activity, activity and osmotic coefficients are of fundamental importance to understand and predict
the thermodynamic behavior of aqueous electrolyte systems. In
order to facilitate the use of mixed electrolytes in these processes,
it is desirable to know accurately the thermodynamic parameters
of the mixture. Study of these electrolytes is fundamentally important to understand the properties and behavior of aqueous multicomponent systems. In the last decades, a series of ion
interaction models for electrolyte solution have been proposed to
predict activity coefficient of each solute and osmotic coefficient
of the aqueous systems. One of the most famous and useful models
is that proposed by Pitzer [8–10]. This model accounts for longrange forces by a classical Debye–Hückel term, while short-range
forces are included via semi empirical parameters. To measure
⇑ Corresponding author.
E-mail address: [email protected] (M.A. Bagherinia).
http://dx.doi.org/10.1016/j.jct.2015.04.001
0021-9614/Ó 2015 Elsevier Ltd. All rights reserved.
the thermodynamic properties in mixed electrolyte solutions, the
most common methods involve the isopiestic vapor pressure
[11,12], vapor pressure lowering [13,14], the electromotive force
(emf) techniques [15,16] and hygrometric method [17]. Among
the various methods, electrochemical cells with ion-selective electrodes (ISEs) because of rapidity and relative simplicity to generate
experimental data are important.
The main goal of this work is to provide precise thermodynamic
data about the ternary system (CaCl2 + Ca(NO3)2 + H2O), which
may allow modeling its behavior. The potentiometric method
was used in this investigation. This paper is the continuation of
the research on binary and ternary electrolyte solutions [18,19].
The potentiometric measurements reported in this work were
carried out on a galvanic cell containing a solvent polymeric
(PVC) Ca2+-ISE and Ag–AgCl electrodes. The measurements were
performed over the ionic strength ranging from (0.0010 to
5.0000) mol kg1 at T = 298.15 ± 0.1 K. For this purpose, a series
of different primary concentrated mixed electrolyte solutions
was used in a standard addition technique to modify the molality
of the mixed electrolyte in the experimental cell. The molal salt
mCaCl
ratios (r ¼ mCaðNO 2Þ ) were 1.00, 2.50, 5.00, 10.00, and 15.00. The
3 2
modeling of this ternary system was based on Pitzer ion-interaction model for mixed electrolyte system and the resulting values
of the mean activity coefficients, osmotic coefficients and excess
Gibbs free energies were reported for the whole series of these
studied ternary mixed electrolyte systems.