无机化学 酸碱中和滴定的指示剂问题（The indicator of acid-base neutralization in Inorganic Chemistry）.doc

无机化学 酸碱中和滴定的指示剂问题（The indicator of acid-base neutralization in Inorganic Chemistry） One of the choice of acid-base neutralization and titration indicators (1) Phenolphthalein: acid alkali titration: color from red just fade Alkaline acid: color from colorless to light red (2) Methyl Orange: when acid is used to titrate bases: the color is yellow to orange Alkaline acid: the color is red to orange Generally do not choose litmus The choice of acid-base neutralization and titration indicator two In order to reduce the method error and make the end-point of titration coincide with the equal point, the appropriate indicator should be chosen. When the strong acid and weak base are titrated each other, methyl orange should be used. Strong and weak interaction should be used in titration, phenolphthalein. Acid and alkali titration can be used each other, methyl orange, can also use phenolphthalein as indicator. Note that not using litmus indicator titration. The reason is the litmus color range (pH5.0 ~ 8) too wide. The change of color at the end of titration is not obvious. It is difficult to observe. The choice of indicator for neutralization titration of acid and base three The commonly used indicator is a weak acid or base, such as phenolphthalein and methyl orange lacmus; organic acid complex. The molecules and ions of an indicator have different colors, and the acid or base solution can affect the ionization balance of the indicator, so the indicator will show different colors in the acid or alkali solution. The choice of indicators in neutralization titration should take the following aspects into consideration: (1) The narrower the color range of the indicator, the better the pH, and the indicator changes the color. Litmus solution due to a wide range of color, and the change point when the color is not easy to observe, so do not use in neutralization titration. (2) It is easy to observe the change of the color of the solution from shallow to deep, but it is diffic