, Volume 26, Issue 10, pp 957-972

Protonation and sodium ion-pairing of the sulfite ion in concentrated aqueous electrolyte solutions

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A protocol has been developed for the reliable titration of aqueous sulfite solutions which minimizes photodecomposition effects. This procedure has been used to measure the protonation constants of the sulfite ion in aqueous solution by glass electrode potentiometry at 25.0‡C and ionic strengths (I) from 0.1 to 5.0M in NaCI media and atI = 1.0M in KC1 and Me4NCl media. These measurements provided evidence of weak but significant ionpairing between SO2/3 -and Na+ with a formation constant of logK Na = 0.431 in 1.0M Me4NCl. This was in very good agreement with the value logK Na = 0.410 measured directly by Na+ ion-selective electrode potentiometry. Evidence is also presented for an extremely weak association of K+ and SO 2 3 -with logK k = 0.22 in 1.0M Me4NCl.