Indian Journal of Chemistry
Vol. 55A, September 2016, pp. 1080-1083
Intermolecular interactions in sulfuric
acid-water system
Renu Loshali* & Narain D Kandpal
Physical Chemistry Laboratory, Department of Chemistry, Kumaun
University, SSJ Campus, Almora 26301, Uttarakhand, India
Email: [email protected]
Received 3 May 2016; revised and accepted 30 August 2016
Viscosity (ƞ) and density (ρ) of aqueous concentrated sulfuric
acid (1.0–9.0) mol dm−3 have been measured at 297.65 K and the
values of A and B- coefficients of Jones-Dole equation have been
calculated from the viscosity data. The value of B-coefficient is
positive which suggests a strong ion-solvent interaction in
aqueous sulfuric acid. It is assumed that in concentrated aqueous
sulfuric acid, HSO53- acts as structure maker. Three concentration
regions of sulfuric acid having value of B-coefficient (measure of
ion-solvent interaction or structure making capacity) in the order
1.0–4.0 mol dm−3 < 4.0–7.0 mol dm−3 < 7.0–9.0 mol dm−3 have
been proposed.
Keywords: Intermolecular interactions, Viscosity, Jones-Dole
equation, Parabisulfate anion
The covalent and non-covalent interactions amongst
molecules may influence the physical, catalytic,
photo-physical and electrochemical properties of
liquids1-3. The water which is used as a universal
solvent interacts with ions (solute) and represents a
central topic in chemistry and biology4. The oxy-acids
may be considered as derivatives of water in which
one hydrogen atom is replaced by an oxy-anion5. The
acidity of an acid increases with the increase in
oxidation number of the atom replacing hydrogen
atom of water whereas in the case of an uncharged
oxy-acids having all oxygen atoms attached to the
central atom, the strength increases with nonhydrogenated oxygen atoms. Sulfuric acid is one of
the oxy-acid of sulphur and forms ionic hydrogen H+,
bisulphate HSO4− and SO42− in water6.
The properties of sulfuric acid in water have been
extensively studied by different methods including
viscometric7-12 and conductometric13-17 studies. In the
low temperature region above 66 wt% of H2SO4, the
structural change in H2SO4/H2O system has two
regions, i. e., 83-85 wt% and 92-94 wt% H2SO4,
where the system contains H2SO4.H2O and eutectic
between H2SO4.H2O and H2SO4 respectively9. In this
study no information was observed regarding the
formation of H2SO4.2H2O (at ≈ 73 wt% H2SO4),
H2SO4.3H2O (at ≈64.5 wt% H2SO4) and H2SO4.4H2O
(at ≈57.6 wt% H2SO4). In the oxidation studies
by Mn(III) in sulfuric acid media, it was observed
that the rate constant decreases with increase in
concentration of H2SO4 (1.0 mol dm−3 to 3.0 mol dm−3)18.
The thermodynamic, spectral and calorimetric studies
are available on sulfuric acid-water system at low
temperature19-21. The studies on temperature
dependence of dissociation of an acid have been
reported in aqueous solution22, 23. In the study on
concentrated H2SO4/H2O binary system, the oxidation
of oxalic acid by vanadium(V) has been studied by
many workers24. The increase in sulfuric acid
concentration in these studies shows that the rate of
oxidation decreases and attains the minimum value at
3.5 mol dm−3 and thereafter rate increases. However,
the structural properties of aqueous sulphuric acid and
the nature of interactions in its concentrated solution,
still require investigation. The viscometric behavior of
concentrated hydrochloric acid has also been
studied25. In view of these observations, viscometric
studies of aqueous concentrated sulfuric acid in the
range of 1.0 mol dm−3 to 9.0 mol dm−3 have been
undertaken in the light of Jones-Dole equation to
obtain additional information about the H2SO4-H2O
system at 297.65 K.
Experimental
The sulfuric acid (~98%) used was of GR grade
(E. Merck). Doubly distilled water was used to
prepare all concentrations of the acid. The strength of
each solution was checked by titrating it against a
standard solution of sodium hydroxide (98%) using
phenolphthalein as an indicator.
The viscosity measurements were made in
calibrated suspended-level viscometers (Infusil India
Pvt. Ltd., BG43500 size 2 and BG43499 size 1). The
viscometer was placed in a thermostated water bath
(Tanco) having accuracy of ±0.1 K for maintaining
constant temperature. The solution of sulfuric acid of
known concentration was taken in the viscometer and
the flow time of the solution was measured with the
help of a stopwatch (Racer). Each measurement was
repeated thrice and an average time of flow was used
NOTES
to calculate the viscosity. The densities of the
solutions were measured using a 15 mL double arm
pyknometer26 having accuracy ±0.00001g/mL and a
single pan electronic balance (Citizen).
Results and discussion
The viscosity of the solution depends on the
sulfuric acid concentration and the temperature of the
solution. There is a deviation in linearity in the
concentration region 4.0 mol dm-3 to 7.0 mol dm-3
with the major deviation at 1.0 mol dm-3 and
9.0 mol dm-3 as shown in Fig. 1. These deviations
indicate the formation of different ionic species. Such
deviations are also observed in reported values of
viscosities10. The measured values of the viscosities
and densities are given in Table 1. The viscosities
measured in the study were used to calculate the value
of η/ηo at each concentration, where η and ηo are
viscosities of the solution and solvent respectively. At
each molar concentration ‘c’, the value of η/ηo is
collected in Table 1. The value of η/ηo obtained at
Fig. 1 – Variation of viscosity (η) of aqueous sulfuric acid with
varying concentrations at 297.65 K.
1081
different concentration were utilized for the
determination of inter-molecular interactions in the
solutions. The interaction parameters were obtained
with the help of Jones-Dole equation27:
(ƞ/ƞ0‒ 1) c‒ 0.5 = A + Bc0.5
… (1)
where A and B are the coefficient for the ion-ion
and ion-solvent interaction respectively and c is the
molar concentration. A representative plot between
(η/ηo-1) c−0.5 and c0.5 is given in Fig. 2. The values of
the linearity coefficient show deviation from standard
value of 1.0, which shows the presence of three
concentration regions due to different nature of
solute-solvent interactions.
The applicability of Jones-Dole equation in the
lower concentration of the sulfuric acid has been
reported in literature17. The validity of Jones-Dole
equation was checked graphically and the plot
displays three straight lines between the concentration
region of 1.0 mol dm-3 to 9.0 mol dm-3. For all three
concentration regions, 1.0 mol dm-3 to 4.0 mol dm-3,
Fig. 2 – Jones-Dole plot of aqueous sulfuric acid of varying
concentrations at 297.65 K.
Table 1 – Values of viscosity (η), density (ρ), η/ ηo and E* of aqueous sulfuric acid + water system at 297.65 K
a
a
c
(mol dm−3)
ƞ
(cP)
c 0.5
(mol dm−3/2)
ρ
(g cm-3)
η/ηo
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
8.5
9.0
1.19
1.44
1.77
2.08
2.49
3.03
3.77
4.44
5.23
5.84
1.00
1.41
1.73
2.00
2.23
2.44
2.64
2.82
2.91
3.00
1.0379
1.0868
1.1431
1.1930
1.2326
1.3041
1.3563
1.3927
1.4212
1.4425
1.20
1.46
1.79
2.11
2.52
3.06
3.81
4.49
5.30
5.90
1/2
(η/ηo-1)c−0.5
(mol−1/2 dm3/2)
0.20
0.32
0.45
0.55
0.68
0.84
1.06
1.23
1.48
1.63
E*
(kJ)
0.43
0.90
1.41
1.81
2.25
2.74
3.28
3.68
4.09
4.36
1.0–4.0 mol dm-3 (B = 0.353 dm-3/2mol-1, A = ‒ 0.162; R2 = 0.99); 4.0–7.0 mol dm-3 (B = 0.789 dm-3/2mol-1, A = ‒ 1.055; R2 = 0.97);
7.0–9.0 mol dm-3 (B =1.612 dm-3/2mol-1, A = ‒ 3.234; R2 = 0.95).
1082
INDIAN J CHEM, SEC A, SEPTEMBER 2016
4.0 mol dm-3 to 7.0 mol dm-3 and 7.0 mol dm-3 to
9.0 mol dm-3, the values of A were calculated from
the intercept and the values of B were calculated from
the slope. The data obtained are recorded in Table 1.
The values of linearities are also given for each
concentration region. The regression results for
Jones-Dole equation comprises a linear relationship
for the obtained concentration regions of H2SO4
although the values of gradients are different. A
comparison of the gradients clearly indicates that
there are three sulfuric acid-water systems between
concentration range of 1.0 mol dm-3 to 9.0 mol dm−3.
Viscosity is a macroscopic property that represents
the average behavior of a large number of water
molecule as reported in the literature28. The increase
in viscosity of solution with the concentration of an
acid can be explained from the rigid nature of
solvation structure formed by the ion and its hydration
shell. The B-coefficient is a measure of order or
disorder introduced in the solvent structure due to
the ion or dipole formed by the solute29. The
B-coefficients calculated with the help of Jones-Dole
equation are positive in all the three concentration
regions, which suggests that sulfuric acid acts as a
structure maker in the concentration range under study.
The strength of solute-solvent interaction increases
with the increasing concentration of the acid.
It is a general concept that molecules must have
sufficient energy to flow in the media. The flow
depends upon the viscosity and temperature. The
Boltzmann factor e−E/RT gives the relationship for
increase in the number of molecules in viscous flow
with the increase of temperature. Hence, the
resistance to flow is reciprocal to the above factor and
viscosity can be given by equation30:
η = Ae E*/RT
… (2)
E* is the energy of activation of the molecule
taking part in a flow of liquid. The value of E* at
different concentration of aqueous sulfuric acid were
obtained from viscosity data are tabulated in Table 1.
The data analysis for rate change of the energy of
activation with concentration in the three different
concentration regions of H2SO4 verifies the presence
of the three concentration regions. In the calculation,
the value of log A has been considered constant and
negligible since the relation between the energy of
activation and value of A follow the same trend.
H+ always exists with HSO4− and hence the
following interaction is proposed as given:
H2SO4 ↔ H+ + HSO4−
H + H2O ↔ H3O+ (ion-solvent interaction)
H3O+ + HSO4− ↔ H4SO5
H2SO4 + H2O ↔ H2SO4.H2O (solvent-solute interaction)
+
Interaction in H2SO4-H2O
Scheme 1
The proposed interaction with water is in
confirmation with the previous studies11, 13. In these
reports, the hydrated sulfuric acid can exists at lower
temperature and higher concentration region. In
general, the value of stability constant increases with
the decrease in dielectric constant and dipole
moments of the solvent31. The dielectric constant of
water has a large value and due to the presence of
hydronium ion it acts as a strong donor solvent which
results in the decrease of the stability constants of
sulfuric acid species.
In this study, we have obtained three specific
regions of concentration which confirm the transition
of species formed between the ions produced by
H2SO4 and water. The stability of the molecule
around the central atom is well known as O2S(OH)25.
The exchange of water molecule with H+ ion is
responsible for the HSO53− species in presence of
H2SO4 because H2SO5, peroxo-monosulfuric acid, is
well known form of peroxy acid of sulphur32. The
ionization of the proposed structure formed by
intermolecular interaction between HSO4− species and
hydronium ion may also maintain the transient
equilibrium in the following manner13:
H4SO5 ↔ 3H+ + HSO53−
H2 + HSO53− ↔ H+ + SO42− + H2O +2e−
Interaction between HSO4− species
and hydronium ion
Scheme 2
The species, HSO53−, has been reported in the
following equilibrium with standard potential –1.0933 V
(ref. 14). The interaction parameters obtained from
Jones-Dole equation for concentration range under
study is in agreement with the proposed solution
structures along with interactions. The main
supporting evidences are as follows: The E* values
increases with increasing concentration of acid which
indicates strong interactions between water and
sulfuric acid molecule. It can be supposed that there
are two association type structures in two distinct
ranges in the higher concentration region whereas in
the lower concentration region, dissociation type
structure is possible which is identified by the slow
NOTES
increase of E* (ref. 33). The complete dissociation of
{3H+ + A3−} type in the sulfuric acid concentration
range of 0.0–3.0 mol dm−3 shows the existence of
H4SO5 species34. The decrease in ionic activity
coefficient values of H2SO4 with the increase of
concentration also supports the assumption drawn and
results obtained in this study35-37. Sulfuric acid has
both uni-univalent electrolytic and bivalent
electrolytic character which explains the different
B-coefficients values in three concentration regions.
The B-value increases from lower concentration
region to higher concentration region, which indicates
the associative character of sulfuric acid species with
solvent water.
In the present study, the presence of HSO53− has
been proposed in aqueous sulfuric acid. In H4SO5, the
four hydroxyl groups are attached to sulfur by a single
bond that belongs to four corners of the base of square
pyramid and the free oxygen atom is bounded to
sulfur atom by double bond at the top corner of the
pyramid. It is concluded that at higher concentration
of sulfuric acid, the concentration of SO42− becomes
negligible in comparison to that of H2SO4, H+ and
HSO4−. At lower concentrations, at or below
3.0 mol dm−3, the presence of undissociated
H2SO4 may be countable and also the dissociation of
HSO4− is very weak. HSO4− ions, presumed in larger
quantity in comparison to SO42− ions in all concentrations,
ranges from 1.0 mol dm−3 to 9.0 mol dm−3. The
interaction parameters obtained from Jones-Dole
equation confirm the presence of three concentration
regions of sulfuric acid in water with following order
of B coefficient (measure of ion-solvent interaction or
structure making capacity): 1.0–4.0 mol dm−3 < 4.0–
7.0 mol dm−3 < 7.0–9.0 mol dm−3. In the
concentration range of 1.0–4.0 mol dm−3, the
existence of HSO53− has been proposed. The
molecules are free to solvate through the formal
negative charges on the O atoms of the ion. In the
concentration range of 4.0–7.0 mol dm−3,
intermolecular association is more effective due to the
large number of bond formation between the solute
and solvent molecules. In the concentration range of
7.0–9.0 mol dm−3, the solute-solvent interaction
attains the higher value and intermolecular forces are
strong due to the formation of hydrated species like
H2SO4.H2O. The study is an illustrative model to
investigate the properties of a solvent for a particular
reaction or industrial process.
1083
References
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Daschakraborty S & Biswas R, J Chem Sci, 124 (2012) 763.
Jabes B S, Agarwal M & Chakravarty C, J Chem Sci,
124 (2012) 261.
Singh M, J Chem Sci, 118 (2006) 269.
Corridoni T, Mancinelli R, Ricci M A & Bruni F,
J Phys Chem:B, 115 (2011) 14008.
Manku G S, Theoretical Principles of Inorganic Chemistry,
(Tata McGraw-Hill Publishing Co Ltd, New Delhi, India)
1980.
Mc Naught A D & Wilkinson A, IUPAC Compendium of
Chemical Technology, 2nd Edn. (Blackwell Scientific
Publication, Oxford) 1997.
Bingham E C & Stone S B, J Phys Chem, 27 (1923) 701.
Wang P, Anderko A & Young R D, Fluid Phase Equil,
226 (2004) 71.
Das A, Dev S, Shangpliang H, Nonglait K L & Ismail K,
J Phys Chem: B, 101 (1997) 4166.
Rhodes F H & Barbour C B, Ind Eng Chem, 15 (1923) 850.
Rhodes F H & Jr. Hodge H B, Ind Eng Chem, 21 (1929) 142.
Srinivasan M K & Prasad B, Trans Faraday Soc, 35 (1939)
374.
Fraenkel D, J Phys Chem:B, 116 (2012) 11678.
Fraenkel D, J Phys Chem:B, 116 (2012) 11662.
Golnabil H, Matloob M R, Bahar M & Sharifian M,
Iranian Phys J, 3-2 (2009) 24.
Wang P, Anderko A & Young R D, Ind Eng Chem Res,
43 (2004) 8083.
Joshi B K & Kandpal N D, Phys Chem Liq, 45 (2007) 463.
Singh R, Tamta D K, Joshi S K, Chandra N & Kandpal N D,
J Chem Pharm Res, 3 (2011) 529.
Kanno H, Chem Phys Lett, 170 (1990) 382.
Guldan E D, Schindler L R & Roberts J T, J Phys Chem,
99 (1995) 16059.
Clegg S L & Brimblecombe P, J Chem Eng Data, 40 (1995) 43.
Clegg S L, Rard J A & Pitzer K S, J Chem Soc Faraday
Trans, 90 (1994) 1875.
Wu Y C & Feng D, J Sol Chem, 24 (1995) 133.
Jones G R & Waters W A, J Chem Soc, (1961)4757.
Loshali R, Chandra B, Sah N & Kandpal N D, Int J Chem
Sci, 12 (2014) 1439.
Nikam P S & Sawant A D, J Chem Eng Data, 42 (1997) 585.
Jones G & Dole M, J Am Chem Soc, 51 (1929) 2950.
Bakker H J, Kropman M F & Omta AW, J Phys: Condens
Matter, 17 (2005) S3215.
Jenkins H D B & Marcus Y, Chem Rev, 95 (1995) 2695.
Fahimuddin H I & Adhami I M, J Pure Appl Sci, 11 (1992) 33.
Kratohvil J & Tezak B, Recueil des Travaux Chimiques des
Pays-Bas, 75 (1956) 774.
Roop R C, Encyclopedia of the Alkaline Earth Compounds,
(Elsevier, The Netherlands) 2012.
Messaadi A, Ouerfelli N, Das D, Hamda H & Hamzaoui A
H, J Sol Chem, 41 (2012) 2186.
Klotz I M & Eckert C F, J Am Chem Soc, 64 (1942) 1878.
Harned H S & Owen B, The Physical Chemistry of
Electrolytic Solutions, (Reinhold, New York) 1958.
Hamer W J, J Am Chem Soc, 57 (1935) 9.
Harned H S & Hamer W J, J Am Chem Soc, 57 (1935) 27.