Mean Activity Coefficients of Peroxodisulfates in Saturated Solutions of the Conversion System 2NH 4. H 2 O at 20 C and 30 C

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1 Mean Ativity Coeffiients of Peroxodisulfates in Saturated Solutions of the Conversion System NH 4 Na S O 8 H O at 0 C and 0 C Jan Balej Heřmanova 5, Prague 7, Czeh Republi balejan@seznam.z Abstrat: Solubility data of the onversion system NH 4 Na S O 8 H O at 0 C and 0 C for the partial pseudoternary systems Na S O 8 (NH 4 ) SO 4 H O, (NH 4 ) S O 8 Na SO 4 H O, Na S O 8 NaNH 4 SO 4 H O and (NH 4 ) S O 8 NaNH 4 SO 4 H O have been orrelated using the relative ativity oeffiient expansion of the rystallizing omponent. The obtained orrelation equations have been used for the alulation of mean ativity oeffiients of ammonium and sodium peroxodisulfates in their saturated solutions of the mentioned pseudoternary systems. Keywords: mean ativity oeffiient, ammonium peroxodisulfate, sodium peroxodisulfate, onversion system Introdution In the previous ontribution (Balej 011a), mean ativity oeffiients (further, term mean is mostly omitted) of sodium, potassium and ammonium peroxodisulfates in pure aqueous solutions in the temperature region (0 50) C have been presented. Another ontribution (Balej 011b) has brought ativity oeffiients of peroxodisulfates in saturated aqueous polyomponent solutions of ternary systems Na S O 8 Na SO 4 H O, K S O 8 K SO 4 H O, (NH 4 ) S O 8 (NH 4 ) SO 4 H O, Na S O 8 NaOH H O, K S O 8 KOH H O, Na S O 8 K S O 8 H O, Na S O 8 (NH 4 ) S O 8 H O, Na - S O 8 H SO 4 H O, K S O 8 H SO 4 H O, (NH 4 ) S O 8 H SO 4 H O, and quaternary systems (NH 4 ) S O 8 (NH 4 ) SO 4 H SO 4 H O, Na S O 8 Na SO 4 H SO 4 H O, and (NH 4 ) S O 8 Na - S O 8 H SO 4 H O. The aim of the present ommuniation is to bring values of ativity oeffiients of ammonium or sodium peroxodisulfate in seleted saturated solutions of the onversion system NH 4 Na S O 8 H O based on the solubility data at 0 C (Balej, Čížek and Thumová 1976) and at 0 C (Balej and Thumová 1976). From the isothermal solubility diagrams of this system, it followed that besides the four solid main substanes, (NH 4 ) S O 8, Na S O 8, (NH 4 ) SO 4 and Na SO 4, the double sulfate NaNH 4 SO 4 H O also exists in the equilibrium with orresponding saturated solutions. Consequently, five different rystallization regions of the given solid substanes are separated by seven binary eutonia lines rossing in three ternary eutoni points at the given temperature. It followed further that no of the rystallization regions of the four mean omponents touhes the rystallization region of the opposite omponent, beause they are always separated by a quite large rystallization area of the fifth omponent, NaNH 4 SO 4 H O. Due to a high number of the original solubility data (totally 05 measurements) bringing results of four diagonal setions, seven binary eutonia lines and three ternary eutoni points at the given temperature, this ommuniation is only limited to the orrelation of the previous solubility data of orresponding peroxodisulfates in four diagonal setions, i.e. (NH 4 ) S O 8 Na SO 4 H O, Na S O 8 (NH 4 ) SO 4 H O, (NH 4 ) S O 8 NaNH 4 SO 4 H O, and Na S O 8 NaNH 4 SO 4 H O at both onsidered temperatures. The first two systems represent pseudoternary systems without any ommon ion, whereas the last two belong to suh ones with a ommon and an unommon ation. The obtained results have been used for the alulation of ativity oeffiients of the orresponding peroxodisulfates in their saturated polyomponent solutions. The solubility orrelation of the onsidered systems was based on the relative ativity oeffiient expansion (Nývlt 1977, Balej 198) (1) Here, so and s denotes the ativity oeffiient of the rystallizing substane in the saturated solution in pure water and in the polyomponent solution, respetively, m C, S and m A, S denotes the molality of Ata Chimia Slovaa, Vol. 6, No., 01, pp , DOI: /as

2 the ation and anion of the rystallizing substane in the saturated polyomponent solution, and m 0, S represents the solubility of the rystallizing substane in pure water, all at the given temperature. The ativity oeffiients of the onsidered peroxodisulfate in the saturated solutions of the onsidered pseudoternary systems have been alulated by two different methods. The first one onsists on the mentioned method of the relative ativity oeffiient expansion of the rystallizing omponent defined by Eq. (1), aording to whih the ativity oeffiient of the onsidered substane in its saturated polyomponent solution is given by the equation 0 exp { () 1 The seond method is based on the thermodynami ondition of the equilibrium between the solid anhydrous eletrolyte of the type 1-, A B, and its saturated solution formulated by the expression (Balej 010a) S % D f G ( C A, r) - D G % f ^C A, aqh f RT - ^m C, S A, S m h p () The equation is valid under the assumption of a omplete dissoiation of the onsidered strong eletrolyte. Here, D f G (C A, r) denotes the standard formation Gibbs energy of the anhydrous solid eletrolyte and D f G (C A, aq) denotes the same quantity of the same eletrolyte in its aqueous solution, respetively. Values of D f G r and D f G aq of the peroxodisulfates at the given temperatures have been taken from the previous paper (Balej 010b), molalities of the appropriate ions in saturated polyomponent solutions have been alulated from the mentioned solubility data originally given in wt. %. Results and Disussion The omposition (in mol kg 1 ) of the saturated solutions of the onsidered ternary systems without a ommon ion, (NH 4 ) S O 8 Na SO 4 H O, at both temperatures is presented in Table 1. The last data at every temperature orrespond to the eutoni solution at whih two solid substanes oexist with the saturated solution. The evaluation of solubility data aording to Eq. (1) led to the expression 0 m { 1 a k ` j 0 ^ thm (4) so that the solubility dependene of the ammonium peroxodisulfate ( ) on the ontent of sodium sulfate (m ) is given by the equation ( t)exp(( t)m ) (5) Here, 0 denotes the solubility of the rystallizing omponen in pure water, t the temperature in C. The same dependene with almost the same auray ould be expressed by an empirial equation Tab. 1. Solubility data and ativity oeffiients in the system (NH 4 ) S O 8 Na SO 4 H O. m solid exp Eq. (5) Eq. (6) Eq. () Eq. () 0 C (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O 8 NaNH 4 SO 4 H O 0 C (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O 8 NaNH 4 SO 4 H O 164

3 t ( t)m (6) Results of the orresponding alulations are given in Tab. 1 as well. As an be seen, the agreement between the measured and alulated values aording to different equations is very good and the mean deviation is always below 0.1 rel. %. Solubility data of the pseudoternary system Na S O 8 (NH 4 ) SO 4 H O at the both onsidered temperatures are given in Table, from whih the following orrelation equation has been obtained: so that 0 m { 1 a k ` j 0 ^ thm (7) ( t)exp(( t)m ) (8) The solubility ould also be expressed by a simpler empiri equation t ( t)m (9) Results of the orresponding alulations are given in Tab. as well. As an be seen, the agreement between the measured and alulated values aording to different equations is in this ase also very good and the mean deviation is always below 0.1 rel. %. At the other two onsidered pseudoternary systems with a ommon ation, the solubility orrelation equation has the following ommon form ^m mh m 4m0 { 1 1 (10) Aordingly, the alulation of the solubility of rystallizing peroxodisulfate ( ) must be performed by the solution of the polynomi equation of the following form m m m 0.5m m 0exp( 1 ) 0 (11) The solubility data of the system (NH 4 ) S O 8 NaNH 4 SO 4 H O are given in Table. The evaluation of solubility data aording to Eq. (1) led to the following expression for the solubility dependene of the ammonium peroxodisulfate ( ) on the ontent of sodium ammonium sulfate (m ) ^m1 mh m1 4m0 { 1 ^ thm ^ thm (1) so that the molality of ammonium peroxodisulfate in the saturated polyomponent solutions has been alulated by the solvation of the polynomi equation m m m 0.5m m 0exp(( t)m (1) ( t)m ) 0 Values of ould also be obtained using a simpler empiri equation t ( t)m (14) The results of alulations are given in Table as well. As an be seen, the agreement between the measured and alulated values of is very good and the mean deviation 0.1 rel. %. The solubility data of the system Na S O 8 NaNH 4 SO 4 H O are given in Table 4. The evaluation of solubility data aording to Eq. (1) led to the following ommon expression Tab.. Solubility data and ativity oeffiients in the system Na S O 8 (NH 4 ) SO 4 H O. m oexisting solid substane exp Eq. (8) Eq. (9) Eq. () Eq. () 0 C Na S O Na S O Na S O Na S O 8 NaNH 4 SO 4 H O 0 C Na S O Na S O Na S O Na S O Na S O 8 NaNH 4 SO 4 H O 165

4 Tab.. Solubility data and ativity oeffiients in the system (NH 4 ) S O 8 NaNH 4 SO 4 H O. m oexisting solid substane exp Eq. (1) Eq. (14) Eq. () Eq. () 0 C (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O 8 NaNH 4 SO 4 H O 0 C (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O (NH 4 ) S O 8 NaNH 4 SO 4 H O ^m1 mh m1 4m0 { 1 ^ thm ^ thm (15) so that the molality of sodium peroxodisulfate in the saturated polyomponent solutions has been alulated by the solvation of the polynomi equation m m m 0.5m m 0exp(( t)m (16) ( t)m ) 0 The same quantity ould be alulated using a simpler empiri equation t ( t)m (17) with a mean deviation 0.08 rel. %. Mean ativity oeffiients of the orresponding peroxodisulfates in their saturated polyomponent solutions have been alulated using Eq. () and Eq. (). The obtained results are given in Tab. 1 4 as well. As an be seen, the individual values of the mean ativity oeffiients of the onsidered peroxodisulfates omputed by both mentioned methods are pratially idential in all ases. From the results, it further follows that in the both pseudoternary systems without a ommon ation, the added omponents enlarge the solubility of the rystallizing peroxodisulfate and onsequently derease its ativity oeffiient, beause the produt onst. (see Eq. 4). This behaviour is totally opposite to that observed at the systems M S O 8 H SO 4 H O with M Na or NH 4 (Balej 011b) where the inreasing ontent of H SO 4 aused a derease of the solubility and onsequently an inrease of the ativity oeffiients of the orresponding peroxodisulfate. Very interesting is the mutual omparison of the influene of individual additives on the final effets expressed as the speifi inrease or derease of the Tab. 4. Solubility data and ativity oeffiients in the system Na S O 8 NaNH 4 SO 4 H O. m oexisting solid substane exp Eq. (16) Eq. (17) Eq. () Eq. () 0 C Na S O Na S O Na S O 8 NaNH 4 SO 4 H O 0 C Na S O Na S O Na S O Na S O Na S O Na S O 8 NaNH 4 SO 4 H O 166

5 Tab. 5. Speifi hange of the solubility D and ativity oeffiient D of the rystallizing omponent of the onsidered systems aused by the added substane. system D D 0 C 0 C 0 C 0 C (NH 4 ) S O 8 Na SO 4 H O Na S O 8 (NH 4 ) SO 4 H O (NH 4 ) S O 8 NaNH 4 SO 4 H O ~ 0 ~ 0 Na S O 8 NaNH 4 SO 4 H O solubility Δ and ativity oeffiients Δ of the rystallizing substane formulated as followed and m Se - m D m me D me e 0 (18) (19) where index e denotes eutoni solution. From the obtained results given in Table 5 it follows that the influene of added ammonium sulfate on the solubility of sodium peroxodisulfate is totally different from that of sodium sulfate addition on the solubility of ammonium peroxodisulfate. While in the first ase the solubility inrease of sodium peroxodisulfate with ammonium sulfate addition at 0 C was more than twie higher than at 0 C, the solubility inrease of ammonium peroxodisulfate with sodium sulfate addition was about twie lower at the same onditions. At systems with a ommon ation, the addition of sodium ammonium sulfate to the rystallizing ammonium peroxodisulfate solution aused a quite distint derease of its solubility, with an almost negligible influene of temperature. The addition of the same double sulfate to the rystallizing sodium peroxodisulfate solution also aused its solubility derease, however, in this ase, the effet was more distint and higher at a higher temperature. What about the influene of the added sulfates on the speifi hange of ativity oeffiients of the rystallizing peroxodisulfates, the final effet was always opposite in omparison to their influene on the solubility hange, in aordane with the theoretial expetation. However, it an ommonly be stated that the values of ativity oeffiients of ammonium or sodium peroxodisulfate in their saturated polyomponent solution differ not too muh from those in pure water at the same temperature, the maximum deviation 1 rel. % has been observed at the eutoni solution of the system Na S O 8 (NH 4 ) SO 4 H O at 0 C. Conlusion The presented results brought the evaluation of the previous solubility data of the onversion system NH 4 Na S O 8 H O at 0 C and 0 C for four seleted pseudoternary systems Na S O 8 (NH 4 ) SO 4 H O, (NH 4 ) S O 8 Na SO 4 H O, Na S O 8 NaNH 4 SO 4 H O and (NH 4 ) S O 8 NaNH 4 SO 4 H O in the form of suitable orrelation equations using the relative ativity oeffiient expansion of the rystallizing omponent. The obtained equations have been used for the alulation of mean ativity oeffiients of sodium and ammonium peroxodisulfates in their saturated solutions of the mentioned pseudoternary systems. It was observed that the values of ativity oeffiients of ammonium or sodium peroxodisulfate in their saturated polyomponent solutions differ not too muh from those in pure water. The presented results represent a supplement of previous papers about the same theme (Balej 198, 011a, b). Referenes Balej J (198) Collet. Czeh. Chem. Commun. 47: Balej J (010a) Collet. Czeh. Chem. Commun. 75: 1 1. Balej J (010b) Z. Phys. Chem. 4: Balej J (011a) Ata Chim. Slov. 4: Balej J (011b) Ata Chim. Slov. 4: Balej J, Čížek M, Thumová M (1976) Collet. Czeh. Chem. Commun. 41: Balej J, Thumová M (1976) Collet. Czeh. Chem. Commun. 41: Nývlt J (1977) Solid-Liquid Phase Equilibria, p Aademia, Prague. 167