Anyone who does science or justinterested in chemistry, it will be interesting to know what an indicator is. Many have come across this concept in chemistry lessons, but school teachers did not provide exhaustive explanations about the principle of the action of such substances. So what is the indicator? Why do indicators change color in solutions? What else are used for? About this later in the article.
Definition
References answer the question thatSuch an indicator is as follows: the indicator is usually an organic chemical compound that is used to determine the parameters of the solution (concentration of hydrogen ions, the equivalence point, and the presence of oxidizing agents). In the narrow sense, the word indicator means a substance that allows you to determine the pH of the medium.
Operating principle
To better understand what an indicator is,consider the principle of its action. As an example, take methyl orange. This indicator is a weak acid, and its general formula is HR. This acid in an aqueous solution dissociates into H ions.+ and R-. H ions+ have a red color, R- - yellow, because in a neutral solution (at pH = 7) this indicator is orange. If there are more hydrogen ions than R-, the solution turns red (at pH <7), and yellow if R ions dominate-. Indicators can be either acids or salts or bases. Their principle of operation is based on simple primary and secondary electrolytic dissociation.
The photo below shows how the color changes.methyl orange depending on the pH. This illustration clearly demonstrates what the indicator is in chemistry and what its purpose is.
Examples of indicators
The most common indicators thatthere is in every school, are litmus and phenolphthalein. Litmus in acid, neutral and alkaline medium has different colors that can not be confused. Paper strips soaked in litmus are placed in a solution and their color changes.
Phenolphthalein takes on a color only in an alkaline medium and becomes raspberry. The available indicator methyl orange is also used.
In the laboratory can be used andless common indicators: methyl violet, methyl red, tenolphthalein. Most of the indicators are used only in a narrow pH range, but there are also universal indicators that do not lose properties at any values of hydrogen.
