Everyone who is engaged in science or is simply interested in chemistry will be interested to know what an indicator is. Many people came across this concept in chemistry lessons, but school teachers did not give exhaustive explanations about the principle of action of such substances. So what is an indicator? Why do indicators change color in solutions? What else are they used for? More on this later in the article.
Definition
Reference literature answers the question of what an indicator is with the following definition: an indicator is usually an organic chemical compound that is used to determine the parameters of a solution (hydrogen ion concentration, equivalence point, determining the presence of oxidizing agents). In a narrow sense, the word indicator is understood as a substance that allows you to determine the pH of the environment.
Operation principle
To better understand what an indicator is, let's consider how it works. Take methyl orange as an example. This indicator is a weak acid and its general formula is HR. This acid isin an aqueous solution, it dissociates into H+ and R- ions. Ions H+ are red, R- - yellow, therefore, in a neutral solution (at pH=7) this indicator is orange. If there are more hydrogen ions than R-, the solution becomes red (at pH < 7), and yellow if R- ions predominate. The indicators can be both acids and s alts or bases. Their operating principle is based on simple primary and secondary electrolytic dissociation.
The photo below shows how the color of methyl orange changes depending on the pH. This illustration clearly demonstrates what an indicator is in chemistry and what its purpose is.
Examples of indicators
The most common indicators that every school has are litmus and phenolphthalein. Litmus in acidic, neutral and alkaline media has different colors that cannot be confused. Paper strips soaked in litmus are placed in the solution and their color changes.
Phenolphthalein acquires color only in an alkaline environment and becomes crimson. The available indicator methyl orange is also used.
In the laboratory, less common indicators can also be used: methyl violet, methyl red, tenolphthalein. Most indicators are used only in a narrow pH range, but there are also universal ones.indicators that do not lose properties at any values of the hydrogen index.
