• MS. 891 /:kc 1rnd1m11<<1 ·I<'•'· / ,,,1L ll 11r / l/ .$ Pr1n1cd •n ( •rc·;11 Britain PHYSICO-CHEMICAL PROPERTIES OF CONCENTRATED SOLUTIONS OF SOME TETRAALKYLAMMONIUM SALTS IN FORMAMIDE IN THE TEMPERATURE RANGE 25-80' MARIO DELLA Mo;-.;1cA and SABINO BLl-'O lnstituto di Chimica-fisica dcll'Universitit. Bari. Italy (Reccit:cd 25 Jrdy 1976) Abstract-- In this work density and viscosity measurements for cnnccntratcd solutions in formamide of Bu 4 NJ. llu 4 NBr. Bu 4 NCL Pr 4 NJ salts in the temperature range 25 80 are reported. The apparent molar volumes ifir arc square root linear functions of the salt concentration. The values of tile partial molar volumes V, decrease when the concentration increases and more over are ahno<;t constant at the last conccntralion used. Viscosity data have hccn analysed using Vand inodcl on viscosity of rigid sphere suspensions. Jn the diluted solution range a different hehavinur between tetraalkyl- ammonium salt solutions and alkaline and alka!ine-canh n1etal ones is shown. This differcricc is inter- preted by supposing that the si7c of alkaline. alkaline-earth metal solvatated cations varies with concen- tration. while the size of tctraalkylammonium solvatcd cations is unchangcahlc. 11\TRODt:CTION In previous papers [I] density, viscosity and electrical conductivity measurements on some uni-univalent and uni-bivalent electrolytes in a solvent with a very high dielectric constant, forman1ide, have been reported. The results of these ITil\:tsurcn1ents have been inter- preted according to soinc theories that have allo\ved a better understanding of the structural configur- ations of concentrated electrolyte solutions. Density investigation on a great number of systems points out that, in the concentrated solution range of many alka- line, alkaline-eart.h salts, a stable solvatation bulk does not develop around each ion, because in these solutions many ions exercise antagonistic interaction powers on so1ne solvent molecules. Partial molar volume values arc therefore un- changeable with the concentration. and arc very close to molar volun1es of pure salts. Viscosity data have been treated with a niodcl [2J that Vand proposed in order to calculate the solvodynan1ic volu1nc of the entities opposing viscous tlux. It has thus been veri- fied that, for c\:ery i·nvestigated system. the applicabi- lity of Vand equation is li1nitcd to very high concen- trations [1]. In order to apply this niodcl to electro- lyte solutions, the ions inust have constant volun1c to different co111.:cntrations. This condition. that i:. verified generally for high charge density cations in the low concentration region: is absent \Vhi!e the solu- tion is concentrating, because of the natural process of the salvation. 'However, we have extended dcnsi111ctric and visco- simetric irivestigation to concentrated solutions of ions which, owing to their structure arc not firmly associated to some solvent molecule in the low con- centration range as well. The choice \Vas in tetrabutylan1n1oniun1 ha!idcs and tctrapropylam1noniu1n iodide. The temperature tested ranges from 25 to So'·. EXPERl:\IE:\T.\L SE(TIO;'\ Baker /\nalysi.!d Reagent forn1a1nidc was purified using a n1cthod reported in hih!ing:raphy LJJ. The product obtained has the following physico-che1nical constants: speci!lc conductance = 4 x 10- 7 cn1- 1 ; density = 1.13030 g/ml (25 ): viscn:.ity 3.35 cP (25· ); dielectric constant = 109.5. (The densities and viscosities of pure forina1nide al nther tcn1pcratun:-;; were: l/ 0 J 5 = l.12259. 1/ 035 = 2.62: i/ 045 = 1.11349. 1/ 045 = 2.13: dn;,n = L1017X. l/or,o = l.6J: doso = J .08366, 1/0HP = J .22.) Viscosity and density 1neasuren1cnts were carried out by procedure and apparatus given elsewhere [ ! _l. The solutions were prepared and \'iscn:.i1nc1er and pycnotneter were Jilkd Jn a dry-box saturated with dry nitrogen. In order to purify [4]. the salts they ha\'C hcen dis- solved in suitable solvents. filtered and rccrystalliLcJ three ti1nes. The solvents used in n:crystalli1.ation \Vere .n1ixturcs uf acetone ·ether for Bu 4 !\Cl {East- man). Bu 4 NBr and Bu 4 NJ and 111cthanol ether for Pr 4 NJ (Fluka). Fnr 1hi"' u:-.c pcrnxiJ rr...:e dry ether \\.·as c1nploycd. The salts v.crc dried 111 a vacuuin oven at 60 on and .rrc:-.ervcd in dcsi- cator on ('aS0 4 . It is \veil knov.-·n that in concentrated aqueous solu- tions and in so1nc different solvents the apparent 1110\ar volun1c nf dcctro!ytcs increases with incri.:aSl: in concentration and ohcy the square-root !aw. obtainable hy the [)chyc 1-llickcl theory [5] and known as Masson's equation [61: ill Density n1easure111ents of and alkaline-earth metal salts in fonnainide ha\'c :.ho\\ n lhat their