Hydrogen Sulfite in Aqueous Solution
J. Phys. Chem., Vol. 100, No. 37, 1996 15117
S2O62 would increase rather than reduce the concentration of
-
) 1.8 × 10 dm mol s-1 was used in evaluating the data, or
8
3
-1
2-
2-
8.5 × 10 dm mol s-1 when 2k18a ) 1.0 × 10 dm mol
3
3
-1
8
3
-1
dithionate, and the independence of the [S2O6 ]/[SO4 ] ratio
with HSO3- concentration also argues against this reaction.
Accordingly, it appears that k4a/k4 has a value in the range 0.30-
.37, but we are unable to determine it more precisely.
Application of the zinc arc lamp allowed a study of the
photooxidation of HSO3 in aerated solution. Although this
process is a chain reaction, the chain length L is rather short.
This parameter is given by the second term on the right-hand
side of eq 4, divided by 2k0[HSO3 ] (two sulfate molecules are
produced in each step), plus a term dealing with propagation
by reaction 18b followed by reaction 17:
-1
20,21
s
was employed.
Within the margin of uncertainty the
present result is consistent with both. Again it appears that a
consensus has been reached on an important rate constant in
the sulfur(IV) chain oxidation system.
Finally it should be mentioned that attempts in the present
study to use either ethanol or 2-propanol as scavengers for SO
0
-
-
4
radicals in the photooxidation of HSO3- failed, because both
alcohols undergo photolysis at the short wavelengths emitted
by the zinc lamp. The photolysis products were the same as
those resulting from the scavenging reaction. Thus it was not
possible to check on the presence of sulfate radicals in the
system. The production of SO4- by reaction 16b appears to be
-
-
1/2
L ) k ([HSO ]/k k18aA) + 2k18b/k18a
A
(E6)
16
3
9
1
1,26
minor according to recent experimental data
for the iron-
-
From the numerical data derived in the Results section one
calculates a chain length of L ≈ 1.5, with the second term in
eq 6 contributing about 25% to the total. The rate of sulfate
production is comparable to that associated with chain termina-
tion by reaction 19. The short chain length in the photooxidation
of HSO3- in acidic solution contrasts with that of SO32- in the
akaline pH region, for which a chain length of about 300 has
been found under similar experimental conditions.6 The major
reason for the difference lies in the smaller value for the rate
catalyzed oxidation of HSO , but it would have been of interest
3
to confirm the extent of SO4- production in reaction 18b, which
contributes to a continuation of the chain.
Acknowledgment. The present work, a contribution to
EUROTRAC Subproject HALIPP, was performed within the
Sonderforschungsbereich 233 (Dynamics and Chemistry of
Hydrometeors), which is supported by the Deutsche Fors-
chungsgemeinschaft.
-
coefficient of the propagation reaction 16 when HSO3 is
4
3
-1 -1
2-
involved (k16 ≈ 1 × 10 dm mol s ) compared to SO3
References and Notes
5
3
-1 -1
(
k16′ ≈ 5 × 10 dm mol s ). In addition it must be noted
(
(
1) Brandt, C.; van Eldik, R. Chem. ReV. 1995, 95, 119-190.
2) B a¨ ckstr o¨ m, H. L. J. Z. Phys. Chem. 1934, 25B, 122-138.
(3) Hayon, E.; Treinin, A.; Wilf, J. J. Am. Chem. Soc. 1971, 94, 47-
that the rate constant for the principal termination reaction in
-
acidic solution, which involves SO5 and HO2, is greater
-
57.
compared with that in alkaline solution, which involves SO5
and O2- (reactions 19a and 19b, respectively). The expression
(4) B a¨ ckstr o¨ m, H. L. J. J. Am. Chem. Soc. 1927, 49, 1460-1472.
(
5) Haber, F.; Wansbrough-Jones, O. H. Z. Phys. Chem. 1932, 18B,
03-123.
(6) Deister, U.; Warneck, P. J. Phys. Chem. 1990, 94, 2191-2198.
7) Huie, R. E.; Neta, P. Atmos. EnViron. 1987, 21, 1743-1747.
(8) Buxton, G. V.; McGowan, S.; Salmon, G. A. In Proceedings of
for the chain length contains the rate coefficients for chain
termination underneath a square root and the rate constants for
the propagation reactions as a proportionality factor. Termina-
1
(
-
tion by the self-reaction of two SO5 radicals is not very
EUROTRAC Symp. ’92; Borrell, P. M., Borrell, P., Cvitas, T., Seiler, W.,
Eds.; SPB Academic Publ.: The Hague, The Netherlands, 1993; pp 599-
604.
9) Yermakov, A. N.; Zhitomirsky, B. M.; Poskrebyshev, G. A.;
Sozurakov, D. M. J. Phys. Chem. 1993, 97, 10712-10714.
10) Connick, R. E.; Zhang, Y.-X.; Lee, S.; Adamic, R.; Chieng, P. Inorg.
-
pronounced as long as HO2 or O2 radicals are present. Buxton
8
et al. have observed much greater chain lengths in the steady
(
state γ-radiolysis of hydrogen sulfite and sulfite, about 75 and
6
100, respectively. In their experiments the formation of HO2
(
-
and O2 radicals was suppressed, and the termination reaction
Chem. 1995, 34, 4543-4553.
(11) Ziajka, J.; Beer, F.; Warneck, P. Atmos. EnViron. 1994, 26A, 2549-
-
was mainly the self-reaction of SO5 radicals, reaction 18a,
which is comparatively slow.
The evaluation of data obtained from the photooxidation
experiments relies on the assignment of S2O8 as sole product
from the self-reaction of SO5 radicals, reaction 18a. This is
the first time that peroxodisulfate was observed as a product in
the photooxidation of S(IV). The rate of S2O8 formation was
used to derive the rate coefficient k19a, which was found to lie
2
5
552.
(
18-536.
(
12) Hatchard, C. G.; Parker, C. A. Proc. R. Soc. London A 1956, 235,
2-
13) Shapira, D.; Treinin, A. J. Phys. Chem. 1973, 77, 1195-1198.
(14) Deister, U.; Neeb, R.; Helas, G.; Warneck, P. J. Phys. Chem. 1986,
-
9
0, 3213-3217.
2-
(15) Weast, R. C., Ed. CRC Handbook of Chemistry and Physics, 64th
ed.; CRC Press: Boca Raton, FL, 1984.
16) Custer, J. J.; Natelson, S. Anal. Chem. 1949, 21, 1005-1009.
(17) Deister, U. Ph.D. Thesis, University Mainz, 1988.
18) Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. J.
Phys. Chem Ref. Data 1988, 17, 513-886.
19) Bielski, B. H. J.; Cabelli, D. E.; Arudi, R. L.; Ross, A. B. J. Phys.
(
9
3
-1 -1
in the range (1.8 ( 1.0) × 10 dm mol s . The wide error
(
margin is partly due to the pH change and its influence on the
-
recombination of HO2/O2 radicals during the photooxidation
process but more importantly due to uncertainties about the
primary quantum yield for the HSO3 photodecomposition.
Nevertheless, the value is in good agreement with one recently
(
Chem. Ref. Data 1985, 14, 1041-1100.
-
(20) Warneck, P., Ed. Transport and Chemical Transformation of
Pollutants in the Troposphere, Part 6: Heterogeneous and Liquid Phase
Reactions; Springer: Berlin, in press.
20,25
derived from pulse radiolysis experiments,
k19a ) (1.7 (
(
21) Buxton, G. V.; McGowan, S.; Salmon, G. A.; Williams, J. E.;
Wood, N. D. Atmos. EnViron. 1996, 30, 2483.
(22) Huie, R. E.; Clifton, C. L.; Altstein, N. Radiat. Phys. Chem. 1989,
9
3
-1 -1
0
.1) × 10 dm mol s . The present value also agrees
9 3 -1 -1
approximately with k19a ) 4.3 × 10 dm mol s , which
3
3, 361-370.
was found necessary to reproduce, by computer simulation,
(
23) Waygood, S. J. In Laboratory Studies on Atmospheric Chemistry;
-
experimental data for the oxidation of HSO3 in the presence
Cox, R. A., Ed.; Commission of the European Communities Air Pollution
Research Report 42; Guyot: Brussels, 1992; pp 23-26.
of iron as catalyst, with and without the addition of benzene as
scavenger for sulfate radicals.11 Thus, a reasonable degree of
consistency has been reached for this rate coefficient from three
different experimental systems.
(24) Herrmann, H.; Reese, A.; Zellner, R. In Proceedings of EUROTRAC
Symp. ’92; Borrell, P. M., Borrell, P., Cvitas, T., Seiler, W., Eds.; SPB
Academic Publ.: The Hague, The Netherlands, 1994; pp 1017-1020.
(
25) Buxton, G. V.; Malone, T. N.; Salmon, G. A. Leeds University, to
The second rate coefficient that was derived from the present
data is k16, which was found to fall in the range k16 ) (1.2 (
be published.
(26) Ziajka, J.; Warneck, P. Ber. Bunsen-Ges. Phys. Chem. 1995, 99,
59-65.
4
3
-1 -1
0
.4) × 10 dm mol s . The steady state γ-radiolysis
8 4 3 -1 -1
experiments gave k16 ) 1.2 × 10 dm mol
s
when 2k18a
JP953236B