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Indicator It's something that indicates or used to indicate . This verb, meanwhile, refers to mean or show something with signals or hints. For example: “The success of a television character of this class is an indicator of the country's cultural decline”, “The government is satisfied with the economic indicator that the International Monetary Fund has just released”, “The arrival of thousands of tourists to the city during the last weekend is an indicator that anticipates a great summer season”.

An indicator can be a physical instrument That indicates something. In this sense, an arrow within a graphic scheme, a traffic signal that warns about the end of a road or the clockwise are indicators.

The indicators or indexes they are also used in the economy , the demography and the sociology . This concept refers to the representation of a reality quantitatively. He Big Mac Index It is an indicator that compares the purchasing power of populations where the chain McDonald's sell your hamburger Big mac . What is done is to convert the price of Big mac to the dollar and compare it in different countries to know if the purchasing power of consumers is high or low.

For everyday language, on the other hand, the indicators are signs that reflect some reality: "That the team has been eliminated as soon as the tournament is an indicator of how bad things are being done".

In the field of chemistry , the substance is known as an indicator that, when added to a sample, produces some chemical change that is noticeable to the naked eye. A clear example is the pH indicator .

PH indicator

The substance used to measure the pH of a medium is known as a pH indicator (index that shows the degree of alkalinity or acidity of a solution; if its value is between 0 and 7, it is an acid solution, while between 7 and 14, a basic one).

In general, the pH indicator is used for chemical substances whose color changes at the same time as the pH, which is related to a change in its structure that is induced by the protonation (the addition of a proton to a molecule, an ion or an atom) or detonation (a molecule yields a hydrogen cation) of the species.

An acid-base indicator has a turning range of one unit above and one below pH, during which the color of the solution in which it is found changes, or it colors (if it were colorless). Some of the most used are the methyl orange, which changes between pH 3.1 and pH 4.4, from red to orange, and phenolphthalein, whose interval of turn goes from pH 8 to pH 10, turning colorless solutions pink or violet.

Litmus paper, on the other hand, is a more economical but less accurate method, and is classified as semiquantitative, which means that it returns an approximate result at the pH of a given solution.

There are also homemade alternatives; for example, if water is boiled with red cabbage (also called red cabbage), turmeric roots (which allow to obtain curcumin), red rose petals, plum skin or purple cabbage (the latter two are used by certain indigenous cultures).

Every pH indicator has a constant protonation, which shows the displacement of the protonation reaction from its basic form. The color change can be seen if the concentration of the basic or acid form is greater than or equal to 10 times that of the opposite.

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