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有些学生认为,在中和实验操作中,多滴加些指示剂,颜色变化会更清楚。但事实并非如此,事实上过乡的指示剂反会使终点颜色变化不明显,甚至还增加实验误差。原因是1.指示剂用量过多,过渡色增加,导之终点颜色变化不明显。2.指示剂本身为有机酸或有机碱,本身也会消耗或代替一些滴定剂,从而带来滴定误差。3.指示剂用量的增加会引起单色变色范围的移动。试液中指示剂的浓度不同,发生变色的pH值也会发生变化。
Some students believe that in the neutralization experiment, add more drops of indicator, the color change will be more clear. However, this is not the case. In fact, the anti-countermeasure indicator will not change the color of the end point obviously, and even increase the experimental error. The reason is 1. too much indicator dosage, the transitional color increases, leading to the end of the color change is not obvious. 2. Indicator itself is organic acid or organic base, itself will consume or replace some of the titrant, resulting in titration error. 3. Increasing the amount of indicator will cause monochromatic discoloration range of movement. The concentration of the indicator reagent in the test solution varies, and the pH value at which the color changes occurs also changes.