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Using a Phenolphthalein pH Indicator


The phenolphthalein indicator is a color change indicator for pH. Its color changes with pH and the fraction of conjugate base present. The indicator changes color over a narrow pH range, from 8.3 to 10.5 (Figure 14.9.2). An excellent way to determine pH is to use the phenolphthalein indicator with a pH meter.

PH of phenolphthalein indicator

A common way of testing the pH of a solution is by using a phenolphthalein indicator. This indicator is a weak acid that can change its color depending on the pH of the solution. It has two different structures: one that absorbs light in the ultra-violet region and another in the visible portion of the spectrum. The pH of a solution can tell us a lot about its composition of a solution.

The pH of a solution is a number between 7.1 and 14, with higher numbers indicating a higher acidity value and a lower number meaning higher basicity. Usually, chemists use litmus paper to test a substance’s pH, which turns red when it comes into contact with a strong acid or a weak base. For example, the PH of phenolphthalein changes color with pH, and the indicator’s color reflects the concentration of the acid or base in the solution.

The PH of the phenolphthalein indicator can be determined by adding a small amount of phenolphthalein solution to a 100 mL sodium hydroxide solution. The phenolphthalein indicator will light pink when the solution is slightly alkaline. The pH of the phenolphthalein indicator is 8.2-10. Above this range, the color changes to purple and becomes colorless.

Color change of phenolphthalein indicator

The color of phenolphthalein changes with pH and a sample’s fraction of hydroxide ions. The indicator’s color changes from pink to orange in a narrow range of pH between 8.3 and 10.5 (Figure 14.9.2). Color change occurs because a chemical reaction occurs in which a molecule changes its shape and charge.

The change of color is caused by a change in the molecule’s electronic structure and the removal of hydrogen ions. This reaction is acid or alkaline-catalyzed. The ionization changes the molecule’s shape and determines how it reacts to light. Phenolphthalein initially appears colorless. However, it blocks blue wavelengths of light. It then turns pink when exposed to an alkaline solution.

In addition to phenolphthalein, other indicators can be used to measure pH. The pH of other indicators differs from that of phenolphthalein, which colors both the acid and the conjugate base. Some indicators can also give color based on pH values, while others can give a series of color changes for the entire pH range.

Methods of pH titration

One of the most common pH titration methods is using a phenolphthalein indicator. The phenolphthalein indicator is a dye that changes color when exposed to an acidic or basic solution. This indicator is used to measure pH in solutions in a range of 8.2 to 10 because it can detect the presence of a small amount of phenol in water.

One of the advantages of this indicator is that it is easy to use and is free from interference with other colors, unlike Methylene blue, which turns pink when exposed to carbon dioxide. This makes it an excellent choice for titrations involving solid acids and bases. However, it is essential to consider the effect of carbon dioxide in the air when using the indicator in acid-base reactions.

In an acid-base titration, two or more solutions are added to a sample to determine the concentration of the acid. In a weak acid-base titration, two different solutions of the weak acid are used. The strength and concentration of the acid are two factors that determine the accuracy of the test.

Cost of phenolphthalein indicator

A synthetic dye that is a colorless molecule in acidic and basic solutions, the phenolphthalein indicator is widely used in titrations. Its production is carried out in the most advanced facilities, with the best quality raw materials, and follows the specifications of the American Chemical Society and NIST Standard Reference Materials. Furthermore, all products are manufactured within the same facility, ensuring complete traceability and consistency.

Phenolphthalein is soluble in alcohol and dimethyl sulfoxide. However, it is not soluble in benzene or ether. It is also insoluble in alkalis, such as sodium hydroxide. It is used in acid-base titrations and in checking the carbonation of concrete, soap, toys, and other substances.

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