HWAHAK KONGHAK, Vol.23, No.4, 231-242, August, 1985
물-메탄올 혼합용매내에서의 NaCl, CaCl2 및 LaCl3의 분몰랄부피 및 Debye-Huckel이론의 적용성에 관한 연구
The Partial Molal Volumes of NaCl, CaCl2 and LaCl3 in Water-Methanol Mixtures and the Applicability of the Debye-Huckel Theory
초록
물-메탄올 혼합용매내에서 NaCl, CaCl2 및 LaCl3의 밀도를 25 ℃에서 측정하여 전해질과 이온의 분몰랄부피 （Vo2 & Voion）를 구한 결과, Debye-Hückel 이론의 적용성은 NaCl>CaCl2>LaCl3의 순서로 감소하며 혼합용매중의 메탄올 함량이 증가함에 따라 감소하였다. 또한 이온의 electrostriction분몰랄부피 (Voelect)는 물보다 메탄올에서 훨씬 큰 값을 가지며 양이온의 원자가가 증가함에 따라 증가하였다. 양이온의 원자가가 증가함에 따른 Voelect in water, Voelect in methanol 및 (Voelect in methanol-Voelect in water)값의 증가분은 각각 25, 55 및 30 ml/mole 정도였다.
0.5∼0.7 몰분율의 메탄올까지는（즉, 혼합용매중의 비교적 물이 많은 영역에서는） 이온주위에서 선택적수화가 존재하며, 이 혼합용매중의 물의 문턱함량을 넘어서면 용매화층이 바뀌면서 용매의 전기적 억압이 급격히 증가함을 알았다.
0.5∼0.7 몰분율의 메탄올까지는（즉, 혼합용매중의 비교적 물이 많은 영역에서는） 이온주위에서 선택적수화가 존재하며, 이 혼합용매중의 물의 문턱함량을 넘어서면 용매화층이 바뀌면서 용매의 전기적 억압이 급격히 증가함을 알았다.
Densities of solutions of NaCl, CaCl2 and LaCl3 in a series of water-methanol mixtures have been measured at 25 ℃．The partial molal volumes of salts V2o and the ionic partial molal volumes Voion in water-methanol mixtures have been detemined.
It was found that the applicability of the Debye-Hückel theory decreases in the order NaCl>CaCl2>LaCl3 and decreases with increasing methanol content in water-methanol mixtures, and that the electrostriction partial molal volumes of ions Voelect are greater in methanol than in water and increase with the valency of the cation. The increments of Voelect in water, Voelect in methanol, and （Voelect in methanol-Voelect in water） with the valency of the cation are approximately 25, 55 and 30 ml/mole, respectively.
The results also indicate that up to 0.5∼0.7 mole fraction of methanol （i.e., in water-rich regions of water-methanol mixtures） the preferential hydration around ion occurs, while above this threshold content of water in these mixtures the change of the solvation layer results in the strong electrostriction of the solvent.
It was found that the applicability of the Debye-Hückel theory decreases in the order NaCl>CaCl2>LaCl3 and decreases with increasing methanol content in water-methanol mixtures, and that the electrostriction partial molal volumes of ions Voelect are greater in methanol than in water and increase with the valency of the cation. The increments of Voelect in water, Voelect in methanol, and （Voelect in methanol-Voelect in water） with the valency of the cation are approximately 25, 55 and 30 ml/mole, respectively.
The results also indicate that up to 0.5∼0.7 mole fraction of methanol （i.e., in water-rich regions of water-methanol mixtures） the preferential hydration around ion occurs, while above this threshold content of water in these mixtures the change of the solvation layer results in the strong electrostriction of the solvent.