• PDF / 632,130 Bytes
• 7 Pages / 603.28 x 783.28 pts Page_size
• 16 Downloads / 205 Views

DOWNLOAD

REPORT

---

I.

INTRODUCTION

PREVIOUSLY, water activities of the solution systems of H2SO4-Fe2(SO4)3-H20 and HC1-FeC13-H20 determined at 298 K by an isopiestic method and a transpiration method, respectively, were reported, and it was found that the Robinson-Bower empirical additivity rule is very useful for evaluating the water activity values of these solution systems. It is impossible to determine the activity values of solutes in those solution systems by the emf method since the redox potential of Fe(III)/Fe(II) significantly affects the emf values. Therefore, the mean activity coefficients of solutes in the solution systems H2SO4-Fez(SO4)3-H20 and HC1FeC13-H_,O were determined by the McKay-Perring method 2 using water activities of the mixed solutions. On the other hand, the mean activity coefficients of solutes in these solution systems can be calculated by applying the GibbsDuhem equation when the activity data of water and one of the solutes of these solution systems are available. Therefore, the calculation of the activity coefficients of Fe2(SO4)3 in the solution systems being studied was demonstrated by applying the Gibbs-Duhem equation to the activity values determined experimentally and those of H2SO4 calculated by the McKay-Perring method. This paper presents the method of activity determination and the activity data of solutes determined for the solution systems H2SO4-Fe2(SO4)3-H20 and HC1-FeC13-HzO at 298 K.

water activity of the mixed solutions. 2 Taking aqueous H2SO4-Fe2(SO4)3 solutions as an example, the calculation procedure used in the present study will be explained according to their method. A modified form of one of those equations which is particularly suitable for application to isopiestic experiments may be written as Eq. [1]. 0.018v(1) l n - ~

_() ( )

/lt

-

f l n ~"2~

'1

'

9 -~

01nx(Z)/a~.~o~ + m*

M-(1)

[1]

9 d In a(H20) m* = m(1) + (v(2)/v(1))m(2) x(2) = (v(2)/v(1))m(2)/m*

where suffixes 1 and 2 denote H2804 and Fe2(SO4)3, respectively, re(i) and y+(i) are the molality and the mean activity coefficient of solute i, respectively, in the mixed solutions, M(i) and F+(i) are the values of m(i) and y+(i), respectively, in an aqueous solution containing the solute i alone, with the same a(H20) values as the mixed solution, and v(i) denotes the number of ions formed by the complete dissociation of one molecule of the solute. Figure 1 schematically shows an equi-a(H20) diagram. To calculate the T+_(H2SO4) in an aqueous HzSO4-Fe2(SO4)3 solution from Eq. [1], it is necessary to calculate the inte-

M(2)

II. DETERMINATION OF MEAN ACTIVITY COEFFICIENTS OF SOLUTES IN T H E SOLUTION

= or, t

SYSTEMS H2SO4-Fe2(SO4)3-H20 AND HCI-FeCI3-H20 BY THE McKAY-PERRING METHOD

A. McKay-Perring Method for the Calculation of Mean Activity Coefficients of Solutes McKay and Perring derived useful equations for calculating the mean activity coefficients of solutes using the HIROSHI MAJIMA, Professor, and YASUHIRO AWAKURA, Lecturer, are with the Department of Metallurgy, Kyoto University, Kyoto, Japan 606. Manusc