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萘红(一作α-萘红,α-naphthyl red)是一种酸硷指示剂。其学名为4-(苯偶氮)-1-萘胺。变色范围为pH4.0～5.0,3.7～5.0或3.7～5.7。在酸性溶液中呈红色或紫色;在硷性溶液中呈橙或黄,独文献给出了过渡区的颜色——褐色。一般配成0.1％乙醇/水(7:3)溶液或0.1％之96％乙醇溶液。鉴于结果参差不一,因此有必要重行观测。我们用国产萘红(实测熔点为121～123℃,文献值为122～124℃,123℃)进行试验。配制1M乙酸(用水稀释14.7毫
Naphthalene red (a-naphthalene red, α-naphthyl red) is an acid-base indicator. Its scientific name is 4- (phenylazo) -1-naphthylamine. Color change range of pH4.0 ~ 5.0, 3.7 ~ 5.0 or 3.7 ~ 5.7. Red or purple in acidic solution; orange or yellow in alkaline solution; the color of the transitional area alone is given in the literature - brown. General dubbed 0.1% ethanol / water (7: 3) solution or 0.1% of 96% ethanol solution. Given the mixed results, it is necessary to revisit the observations. We use domestic naphthalene red (measured melting point of 121 ~ 123 ℃, the literature value of 122 ~ 124 ℃, 123 ℃) were tested. Prepare 1 M acetic acid (14.7 milliliters in water