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[Chemical Knowledge]：What is the indicator

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An indicator is a chemical substance that has the ability to change color. It is often used in analytical chemistry and chemical experiments to indicate the progress and end point of a chemical reaction. The indicator can help the chemical experimenter to judge the nature, state and result of the chemical reaction by showing the nature of different colors under different chemical conditions.

Because chemical reactions produce different results under different chemical conditions, the use of indicators can help chemical experimenters determine the moment to reach a specific condition, such as the end of a chemical reaction, reaching a specific pH, etc. At the same time, the indicator can also help the chemical experimenter to confirm the type of certain reactions, such as redox reactions, acid-base neutralization reactions, etc. Types of

Indicators

There are many types of common indicators, the most common of which is acid-base indicators. Acid-base indicators are classified according to the color change at different pH values. They are one of the most commonly used and useful reagents in chemical laboratories, with simple operation, high sensitivity and wide range of use.

For example, phenolphthalein is a commonly used acid-base indicator. It is colorless under weakly acidic conditions and becomes dark red under neutral or weakly alkaline conditions. When the pH value of the reactant reaches the transition point, the color of phenolphthalein will change, indicating that the chemical reaction has reached a specific stage. Another common indicator

is a complexation indicator, also called a coordination indicator. It is based on the change in color when weaker complexes form stronger complexes. The presence of metal ions can be detected and separated from other ions using a complexing indicator.

For example, Aegean Blue (Eriochrome Black R) is a commonly used complexing indicator for detecting the presence and separation of metal ions such as calcium and magnesium.
Precautions for
use of indicators

When using indicators, you should pay attention to the following points:

1. Use the correct indicator. Because different indicators will show different color characteristics under specific chemical conditions, the indicator should be selected correctly according to the needs of chemical experiments.

2. The color characteristics and chemical reaction conditions of various indicators are well known. Only when the characteristics of the indicator are well known and the correlation between the properties of the indicator and the reaction conditions is understood, can the chemical experiment be better assisted and guided.

3. Appropriate control of the use of indicators. The indicator should be used in an appropriate amount, otherwise it will cause the chemical reaction to lose the corresponding control, which will have a negative impact on the chemical experiment.

4. Treat different types of indicators separately to avoid confusion. Different indicators should be treated separately during use to avoid confusion and cause unnecessary trouble or harm.

indicator, as an indispensable reagent in chemical experiments, plays an important role in judging the progress and results of chemical reactions. Therefore, it is necessary to strictly control the amount of use, understand the characteristics of the indicator and its correlation with the reaction conditions, and choose different indicators according to the experimental needs.