Departmental Bulletin Paper 酢酸およびアンモニアの電離平衡の移動に関するマイクロスケール実験で使用する酸塩基指示薬溶液の濃度に関する考察―メチルオレンジ水溶液およびフェノールフタレイン溶液の有効濃度―

中川, 徹夫  ,  Tetsuo, NAKAGAWA

Adding a little solid sodium acetate to an aqueous acetic acid solution causes the displacement of ionization equilibrium as confirmed by the color change of aqueous methyl orange solution from red to orange. Adding a little ammonium chloride to an aqueous ammonia solution also confirms the displacement of ionization equilibrium by the color change of phenolphthalein solution from red to colorless or pale pink. The amount of acid-base indicators such as methyl orange and phenolphthalein must be reduced in microscale expriments on the displacement of ionization because of the need to limit the amount of aqueous solution of acetic acid and ammonia. Therefore, commercial 0.1 W/V % aqueous methyl orange, 1.0 W/V % phenolphthalein solutions, and their diluted solutions by 5,10, and 20 times using their solvents were used in this expriment on the displacement of ionization equilibrium. Even the 0.01 W/V % aqueous methyl orange solutions (diluted by 10 times) and 0.05 W/V % phenolphthalein solutions (diluted by 20 times) were effective for aqueous acetic acid and ammonia solutions respectively in this microscale experiment.

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