Formation Quotients of Aluminum Sulfate Complexes in NaCF3SO3 Media at 10, 25, and 50 C from Potentiometric Titr
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- 作者：Caibin Xiao ; David J. Wesolowski ; and Donald A. Palmer
- 刊名：Environmental Science & Technology
- 出版年：2002
- 出版时间：January 15, 2002
- 年：2002
- 卷：36
- 期：2
- 页码：166 - 173
- 全文大小：112K
- 年卷期：v.36,no.2(January 15, 2002)
- ISSN：1520-5851
文摘
Mercury/mercurous sulfate electrode concentration cells(with liquid junction) are employed in this study to determinethe formation constants of aluminum sulfate complexes,with the principal advantage that the change in the freesulfate concentration is measured directly without theneed to know the standard potential of the electrode.Potentiometric titrations were conducted at temperaturesof 10, 25, and 50 
s/entities/deg.gif">C and ionic strengths of approximately0.3, 0.5, and 1.0 molal in aqueous solutions of the inert 1:1electrolyte sodium trifluoromethanesulfonate (NaTr).Stoichiometric molal formation quotients Q1 and Q2,respectively, for the reactions Al3+(aq) + SO42-(aq) s/entities/rlhar2.gif">AlSO4+(aq) and Al3+(aq) + 2SO42-(aq) s/entities/rlhar2.gif"> Al(SO4)2-(aq) weredetermined. The values of log Q1 obtained from thiswork in NaTr media at ionic strengths of 0.3 and 1.0 mol·kg-1and 50 s/entities/deg.gif">C (1.72 ± 0.08 and 1.35 ± 0.06, respectively) arein excellent agreement with the values (1.71 ± 0.2 and 1.32± 0.1) determined in NaCl media from the recentpotentiometric study conducted in the same laboratoryusing a hydrogen electrode concentration cell by Ridleyet al. (Ridley, M. K.; Wesolowski, D. J.; Palmer, D. A.; Kettler,R. M. Geochim. Cosmochim. Acta 1999, 62, 459-472).The value of log Q2 (2.05 ± 0.05) in 1.0 mol·kg-1 from thiswork is smaller than the value reported by Ridley et al.(2.6 ± 0.5) but within the combined experimental error.Empirical isothermal equations are presented to permitcalculation of the equilibrium quotients as a function of ionicstrength (0-1 mol·kg-1), giving log K1 and log K2 valuesat 25 s/entities/deg.gif">C and infinite dilution of 3.84 ± 0.12 and 5.58 ± 0.09,respectively. The value for log K1 obtained in this studyat 25 s/entities/deg.gif">C is bracketed within experimental uncertainty byvalues reported by Kryzhanovskii et al. (Kryzhanovskii, M. M.;Volokhov, Y. A.; Pavlov, L. N.; Eremin, N. I.; Mironov, V. EZh. Prikl. Khim. 1971, 44, 476-479) and Nishide and Tsuchiya(Nishide, T.; Tsuchiya, R. Bull. Chem. Soc. Jpn. 1965, 38,1398-1400), namely, 3.89 and 3.73, respectively. All otherliterature values for the first aluminum sulfate associationconstant are considerably lower than these results, whichis also true for the second association constant, althoughthere are few experimental data available for the latter.Empirical equations are also presented for calculatingvalues of log Q1 and log Q2 from 0 to 1 molal ionic strengthand from 10 to 125 s/entities/deg.gif">C, spanning the range of mostenvironmental conditions at which these reactions areimportant.