What Is Phenolphthalein?
Phenolphthalein is an organic compound with the chemical formula C20H14O4.
It is used as an acid-base indicator in analytical chemistry because its solution color changes depending on pH.
The CAS number is 77-09-8. It has a molecular weight of 318.32, a melting point of 258-263°C, and is a white or pale yellow solid at room temperature. It is insoluble in water.
In other solvents, it is slightly soluble in ethanol, insoluble in diethyl ether, insoluble in benzene, and slightly soluble in DMSO. Its density is 1.277 g cm-3.
Uses of Phenolphthalein
A typical use for phenolphthalein is as an acid-base indicator in analytical chemistry. Phenolphthalein is dissolved in ethanol or a mixture of ethanol and water to form a solution of Phenolphthalein, which turns reddish purple when basicity is detected.
One example of application of its properties as an acid-base indicator is in concrete inspection. As concrete deteriorates, carbonate is formed and the pH decreases. Therefore, Phenolphthalein can be used to check the deterioration of concrete based on the principle that only new concrete will color and old concrete will not.
Other applications include blood detection (Casull-Meyer test), cadmium and gold detection, matting ink, and hair dye for toy dolls. It was once used as a laxative, but is no longer used clinically due to its suspected carcinogenicity in rodent experiments.
Characteristics of Phenolphthalein
Phenolphthalein is synthesized by heating and mixing phthalic anhydride and phenol under acidic conditions, resulting in the condensation of two molecules of phenol for one molecule of phthalic anhydride. It is characterized by the possibility of alteration by light.
Therefore, it must be stored away from high temperatures and direct sunlight. In addition, mixing with strong oxidizers is hazardous, and decomposition products include carbon monoxide (CO) and carbon dioxide (CO2).
Types of Phenolphthalein
Phenolphthalein is sold by reagent manufacturers primarily as a reagent and indicator for testing and research. In addition to the pure product, there is a 1.0w/v% ethanol solution product that can be used as-is as an indicator for neutralization titration.
The purity products are available in 25g, 100g, 500g, etc. The 1.0 w/v% ethanol solution products are available in volumes of 100mL, 500mL, etc. They are treated as reagent products that can be stored at room temperature. These are reagents that can be stored at room temperature.
To prevent alteration by light, brown glass bottles may be used for packaging.
Other Information on Phenolphthalein
Phenolphthalein in Analytical Chemistry
Phenolphthalein solution is characterized by a color change with pH. It is widely used as an acid-base indicator because the color change is clear and is not easily affected by coexisting substances.
It is colorless in acidic conditions below pH 8.3, pink to reddish purple in basic conditions between pH 8.3 and 13.4, and colorless again in more basic conditions than pH 13.4. This is due to the fact that, under basic conditions, the phenol moiety undergoes deprotonation, resulting in a change in molecular structure.
Regulatory Information on Phenolphthalein
Phenolphthalein is known to be harmful to the human body, including the risk of carcinogenesis and hereditary diseases. For this reason, it has been designated as a “hazardous and toxic substance.”