论文部分内容阅读
在某些酸碱滴定中,因 pH 突跃范围很窄,使用一般指示剂难以判断终点,这时可使用混合指示剂或称改良指示剂来克服这种弊病。混合指示剂具有颜色变化明显易于观察,变色范围较为狭窄的特点。混合指示剂通常是由一种指示剂与某种不随 pH 变化而改变颜色的惰性染料混合而成或随 pH 改变而改变颜色的两种不同的指示剂混合而成。例如测定5%碳酸氢钠注射液的含量时以甲橙为指示剂,其滴定终点是橙红色,这种颜色的变化人眼较难观察,难以掌握得很准确,因而容易产生较大误差。
In some acid-base titrations, because of the narrow range of pH abruptness, it is difficult to judge the end point using a common indicator, and mixed indicators or modified indicators can be used to overcome this disadvantage. Mixed indicator with a clear change in color is easy to observe, the color range of more narrow features. The mixed indicator is usually composed of a mixture of two different indicators of an indicator mixed with some inert dye that does not change color with pH or with a change in color with pH. For example, the determination of 5% sodium bicarbonate injection with methyl orange as indicator, the end point of the titration is orange-red, this change in color is difficult to observe the human eye, it is difficult to grasp very accurate, and therefore prone to greater error.