Indicators of acid-base

Indicators of acid-base - organic substances, which change the character of the colour (bi-color LEDs) or its intensity (monochrome indicators) at change the pH of the environment.
The two-color examples of indicators can serve as a litmus paper of blue in alkaline medium and red in acidic or methyl orange - yellow in alkaline and pink in acid medium; - to one-color indicator is phenolphthalein is colorless in acid medium and raspberry in alkaline.
Indicators are weak organic acids or weak organic bases, painting medicationovernight molecules which is different from the color formed by them organic ions. So, medicationabana molecules weak acid phenolphthalein is a colourless, and formed it anions crimson. When you change the pH of the environment is changing the ratio between the number medicationovernight molecules and ions, resulting in discoloration of the indicator. Change the color of the indicator is inherent in each indicator narrow range of pH environment (area changes the color of the indicator).
Area changes the color methyl orange is at pH=3,0-4,4; at pH<3,0 this indicator rose, at pH>4,4-yellow. The gradual change its colour from pink to yellow happens when you change the pH of the environment from 3.0 to 4.4.
Indicators are used: to determine the end of titration (see) in the determination of acidity of gastric juice, as well as the content of acids and alkalis in the various solutions (see Neutralization method); for colorimetric determination of pH biological liquids; for qualitative determination of acidity or alkalinity of the environment. For all these purposes the indicators used as an aqueous and alcoholic solutions or as a special indicator of paper (a strip of filter paper soaked in the solution of indicators).
Radioactive indicators - see Isotopes.