摘要
本研究目的是以實驗方法量測CaCl2、MgCl2及BaCl2
2：1單電解質水溶液在溫度298.15 K下、不同濃度的個別離子活性係數；並且量測CaCl2單電解質水溶液在不同溫度下、不同濃度的個別離子活性係數。因為缺乏鎂及鋇離子選擇性電極，所以本實驗使用氯離子選擇性電極來量測電動勢，以無因次電位法來計算Cl-的活性係數，接著使用平均離子活性係數之文獻值，計算出Ca2+、Mg2+及Ba2+的活性係數。
實驗結果顯示，個別離子活性係數不僅與濃度、溫度有關，而且與其相對離子也有很大的關係。在溫度效應下，固定濃度的單電解質水溶液其離子活性係數隨著溫度的升高而減小。在298.15 K時，相對離子皆為Cl-的2：1單電解質水溶液，陽離子活性係數的大小順序依次為Mg2+＞Ca2+＞Ba2+，且其相對Cl-活性係數皆不相同。
把個別離子活性係數以Khoshkbarchi-Vera方程式及雙離子參數離子活性係數模式（two-ionic-parameter approach）來關聯，均有不錯的結果。最後，使用雙離子參數離子活性係數模式關聯數據所得到的參數，計算2：1單電解質水溶液的滲透壓係數，並與文獻值作比較，其平均相對誤差（AARD）小於2﹪。

Abstract
In this study, the ionic activity coefficients of Ca2+, Mg2+, Ba2+, and Cl- were determined. The activity coefficients of Ca2+ and Cl- were measured with individual ion selective electrode (ISE). Due to the lack of ion selective electrode of magnesium and barium, the activity coefficients of these ions were calculated by using the literature data of the mean activity coefficients of the salts of these anions.
The experimental results show that the individual ion activity coefficients depend on concentration, temperature and the nature of its counterion. The ionic activity coefficient in aqueous solution decreases with increasing temperature at constant concerntration. The activity coefficient of the cation in the presence of Cl- decreases in the order of: Mg2+＞Ca2+＞Ba2+.
The Khoshkbarchi-Vera equation and the two-ionic-parameter approach were used to correlate the the individual ion activity coefficients with good accuracy. Finally, the approaching and solvation parameters of two-ionic-parameter approach were used to calculate the osmotic coefficient for these 2:1 electrolytes in aqueous solutions. The average absolute relative deviations (AARD) of the osmotic coefficient are ＜2﹪.

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