Determination of the Acidity Constants of Methyl Red and Phenol Red Indicators in Binary Methanol− and Ethanol−Water Mixtures

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• 作者：Rafif K. Srour ; Louis M. McDonald
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2008
• 出版时间：January 2008
• 年：2008
• 卷：53
• 期：1
• 页码：116 - 127
• 全文大小：274K
• 年卷期：v.53,no.1(January 2008)
• ISSN：1520-5134

文摘

The conditional acidity constants, pK_a, of methyl red and phenol red were determined in (10, 30, and 50) wt % binary aqueous mixtures of methanol and ethanol at 298.15 K and at constant low ionic strength (2.5·10⁻³ mol·dm⁻³) by a spectrophotometric method. For methyl red and phenol red and in the studied cosolvent + water systems, pK_a ranged from 3.78 ± 0.06 to 5.50 ± 0.04 and 8.50 ± 0.1 to 6.71 ± 0.03, respectively. Variations in the pK_a of methyl red and phenol red as functions of wt % cosolvents are discussed in terms of solvent properties.