Bisulfite HSO

Depending on the ratio of SO2 to base, sulfur in the cooking Hquor can be present in several forms. There may be dissolved SO2 sulfurous acid, H2SO2 bisulfite, HSO and monosulfite, ions. The bisulfite may be present alone or in combination with two other forms. Conventionally, the... 

In sequence A, bisulfite is consumed directly. In sequence B, the net reaction is destruction of HSO, with no change in the SO concentration.)... 

Fig. 5.2.9. Absorption spectra of spent liquors of a magnesium bisulfite pulping sequence for spruce. The spectra are measured against water (resolution 4cm 1, 64 scans). 1331, 1150 free S02 1200, 1064, 1022 HSO, 1037 lignosulfonates 1512 aromatic skeletal vibrations of lignin other identified bands indicate increases in the concentrations of organic constituents in the liquor...

Strictly, SO2 dissolves in water as (S02)aq with little forming sulfurous acid, H2S03(aq>, but it is usual to neglect the distinctions between these two species. The ionization equilibria are typically fast and in the case of the hydration of aqueous SO2 the hydration reaction proceeds with rate a constant of 3.4 X 10 s which allows the formation of the bisulfite anion to be exceedingly rapid. Although H2S03(aq) is a dibasic acid, the second dissociation constant is so small that the bisulfite anion (HSO ) dominates as the subsequent dissociation to the sulfite ion S03(aq> would not be important except in the most alkaline of solutions. At around pH 5.4 in a typical cloud with a gram of liquid water in each cubic meter, SO2 will partition equally into both phases, because of the hydrolysis reactions. 

In addition to the S(IV) —H202 reaction, the reactions of other peroxides such as peroxymonosulfate, peroxyacetic acid, and methyl hydroperoxide with S(IV) are also sensitive to specific-acid catalysis (Hoffmann and Calvert, 1985). The rate of oxidation of S(IV) by HSO / is comparable to the rate of oxidation of S( IV) by hydrogen peroxide (Betterton and Hoffmann, 1988). We have proposed a general mechanism for the ROOH-S(IV) reaction in which the rate-determining step involves the acid-catalyzed decomposition of a peroxide-bisulfite intermediate. The rate expression applicable for this mechanism is... 

The aqueous-phase conversion of dissolved S02 to sulfate is probably the most important chemical transformation in cloudwater. Dissolution of S02 in water results in the formation of three chemical species hydrated S02(S02 H20), the bisulfite ion (HSO-(), and the sulfite ion (SO ). At... 

Anthocyanin solutions are strongly bleached in the presence of sulfur dioxide. At a pH of 3.2, 96% of the sulfuric acid (SO2 + H2O) consists of HSOs" (bisulfite) anions that react with the flavylium cation, most probably on carbon 2 by analogy with the hydration reaction. The product formed is colorless ... 

Values for K in Tables II, III, and IV were derived by calculation of all uncombined sulfite as free sulfurous acid. This approach lacks validity to a certain extent since it assumes only HSOj", free sugar, and bisulfite addition compound in the equilibrium. Obviously, this is hardly possible in systems the pH values of which are so high or so low that little or no HSOa ion is present. In fact, the addition compounds obtained at the upper ranges might actually be some type of aldehyde-sulfite rather than aldehyde-bisulfite. There is an almost complete lack of quantitative application of the concept of variant HSOa ion content in sugar work however, Sundman did extend some of his data (Table II) by computing K on the basis of HSO rather than total sulfur dioxide calculated as bisulfite. The results are shown in Table V. 

Simenson (1940), and the thermodynamic data for the system SO2-H2O are given by Plummer (1950). In water sulfur dioxide exists as the dissolved gas, as undissociated sulfurous acid, H2SO3, as the bisulfite ion, HSOj , and as the sulfite ion, SO3—. Sulfurous acid is a rather weak dibasic acid its first ionization constant is 1.7 X 10 , and the second is 5 X 10 . At 25° C. the corresponding pK values are 1.8 and 5.3, respectively. The calculated distribution of the various ionic species in aqueous solution of sulfurous acid in the range of pH of 0 to 8 is shown in Fig. 1. At pH s over 9.5 only SO3 ions exist, in the range of pH 9.5 to 4.5 both SO3 and HSOs occur, and at pH 4.5 and lower, SO3— no longer exists in appreciable concentrations. 

SODIUM ACETATE. Na CH, COO SODIUM BICARBONATE, Na HCO, SODIUM BISULFATE. Na HSO, SODIUM BISULFITE. Na HSOa... 

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