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Phenolphthalein is used in toys, for example as a component of disappearing inks, or disappearing dye on the "Hollywood Hair" Barbie hair. In the ink, it is mixed with sodium hydroxide, which reacts with carbon dioxide in the air. This reaction leads to the pH falling below the color change threshold as hydrogen ions are released by the reaction:
In a titration of a weak acid with a strong base the pH rises more steeply as the end-point is approached. At the end-point, the slope of the curve of pH with respect to amount of titrant is a maximum. Since the end-point occurs at pH greater than 7, the most suitable indicator to use is one, like phenolphthalein, that changes color at high pH. [2]
Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent.It is applicable to both organic compounds and inorganic compounds and may be used with or without an enzymatic stage.
Hence, a pH indicator is a chemical detector for hydronium ions (H 3 O +) or hydrogen ions (H +) in the Arrhenius model. Normally, the indicator causes the color of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their odor.
In order to generate the intense pink color indicative of a positive test, the reduced phenolphthalein must be oxidized back to its normal, colored form. In the relevant reaction, hydrogen peroxide reacts with the hemoglobin in the blood. Phenolphthalein does not directly participate in this process; instead, it acts as an external source of ...
The color-change that occurs in the blue bottle experiment has features of a clock reaction, in which a visible change in the concentration of one or more reagents suddenly occurs upon the exhaustion of a limiting reagent. For example, the limiting reactant, oxygen, is consumed by another reactant, benzoin, with the help of safranin as a ...
This color change is an indication that even in the absence of contamination, the medium needs to be replaced (generally, this should be done before the medium has turned completely orange). Since the color of phenol red can interfere with some spectrophotometric and fluorescent assays, many types of tissue culture media are also available ...
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. [1] It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex. Complexometric indicators are also known as pM indicators.