著者

野口 大介

出版者

長崎大学大学院工学研究科

雑誌

長崎大学大学院工学研究科研究報告 = Reports of Graduate School of Engineering, Nagasaki University (ISSN:18805574)

巻号頁・発行日

vol.52, no.98, pp.86-93, 2022-01

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Methyl Orange (MO), one of the water-soluble azo dyes, is well-known as pH indicator extensively used in secondary schools and post-secondary education institutions of chemistry. Besides, azo compounds are applied widely in imaging industries including the textile, paper, printing, and food industries. In the present study, researches on the chemical structures of MO, the positions H+ attaches in MO appear to be unclear, are described historically, dealt with acid-base reaction, ammonium-azonium tautomerism in acidic aqueous solutions by means of UV-Vis spectroscopy. Furthermore, problems in the textbooks of analytical chemistry due to misunderstanding the difference between resonance theory and tautomerism are pointed out for precise learning the structures of MO and its protonated species in an aqueous solution. X-ray crystal structures of MO are shown to support teaching students of chemistry too.