Phenolphthalein – C20H14O4

Phenolphthalein (C₂₀H₁₄O₄) is an organic chemical compound often used as an indicator in acid-base titrations. It is slightly soluble in water and usually is dissolved in alcohol in experiments. It is a weak acid and belongs to the phthalein dyes class. Phenolphthalein is colorless below pH 8.5 and attains a pink to deep red hue above pH 9.0.

In this article, we will look into What is Phenolphthalein, Phenolphthalein Formula, Phenolphthalein Structure, Uses of Phenolphthalein, and others in detail.

What is Phenolphthalein?

Phenolphthalein is a chemical indicator, it is a weak acid and belongs to the class of dyes known as phthalein dyes. It is synthesized from phthalic anhydride and two equivalents of phenol under acidic conditions. Phenolphthalein is also known for its use as a pH indicator and laboratory reagent. It is also used as a laxative, although its use in this capacity has decreased due to safety concerns.

Phenolphthalein Molecular Formula	C20H14O4
Phenolphthalein Molecular Weight/ Molar Mass	318.32 g/mol
Phenolphthalein Density	1.277 g/cm3
Phenolphthalein Appearence	White Powder
Phenolphthalein Melting Point	258–263 °C

Phenolphthalein in Acid

Phenolphthalein in acid is colourless.

Phenolphthalein in Base

Phenolphthalein in base turns to pink color.

Phenolphthalein(C₂₀H₁₄O₄) Formula

Phenolphthalein is a chemical compound whichhas 20 carbon atom, 14 hydrogen atom, and 4 oxygen atom, and it has the formula,

Chemical Formula of Phenophthalein: C₂₀H₁₄O₄

Phenolphthalein(C₂₀H₁₄O₄) Structure

Phenolphthalein has a complex structure and it has three benzene ring and its structure is added in the image below,

• It contains a phenyl group, which is an aromatic hydrocarbon, bonded to a phthalate group, which is a plasticizer.

• Phenolphthalein molecule has three hexagonal structures, one pentagonal structure, two alcoholic groups, and one ketone group.

• Carbon, hydrogen, and oxygen chains form the structure of Phenolphthalein.

Properties(C₂₀H₁₄O₄) of Phenolphthalein

Various properties of Phenolphthalein are added in the table below,

Feature	Phenolphthalein
IUPAC Name	3,3-bis(4-Hydroxyphenyl)-2-Benzofuran-1-one
Appearance	White to yellowish-white or pale orange fine crystalline powder
Solubility	Slightly soluble in water, readily soluble in alcohol
Weak acid	Phenolphthalein is a weak acid
Melting point	258-263°C
Density	1.277 g/cm³
Synthesis	Phenolphthalein is synthesized by condensing phthalic anhydride with two equivalents of phenol under acidic conditions
pKa	Phenolphthalein has a pKa of 9.1, indicating that it is a weak acid

Acid-Base Indicator Property

Phenolphthalein is a weak acid that can lose H⁺ ions in solution, and its different forms in aqueous solution depend on the pH, enabling it to function as an acid-base indicator.

Phenolphthalein Test

Phenolphthalein test is a presumptive test used for the identification of blood. It is based on the catalytic peroxidase-like activity of the heme group in hemoglobin, which is present in red blood cells. In the presence of hydrogen peroxide, this peroxidase-like activity catalyzes the oxidation of Phenolphthalin, a colorless compound, into Phenolphthalein, which is pink in color. The test is conducted on suspected bloodstains before collection.

How to Use Phenolphthalein Indicator

To use Phenolphthalein as an indicator, follow these steps:

• Prepare Indicator Solution: Dissolve a known amount of Phenolphthalein in a suitable solvent, such as ethanol or water, to create a solution with a known concentration.

• Add Indicator Solution to Test Solution: Add a few drops of the Phenolphthalein solution to the test solution, which could be an acidic or basic solution, depending on the test’s purpose.

• Observe Color Change: The color change indicates the pH of the test solution.

• Record Results: Document the color change observed in the test solution, as this information can be used to determine the acidity or basicity of the solution.

Color Changes in Acidic and Alkaline Solutions

Color Changes in Acidic and Alkaline Solutions is observed as,

• Color of Phenolphthalein in Acid: Phenolphthalein is colorless in Acidic Solutions

• Color of Phenolphthalein in Base: Phenolphthalein turns pink to deep red in Basic Solutions around pH 9

Uses of Phenolphthalein

Phenolphthalein is an organic compound with various applications, including:

• pH Indicator for Concrete Carbonation: Phenolphthalein can be used as a pH indicator for determining concrete carbonation.

• Disappearing Ink: Phenolphthalein can create disappearing ink, which changes color when exposed to air.

• Color-Change Toys: Phenolphthalein is used to produce color-change toys, such as “Hollywood Hair” Barbie.

• Colored Bubbles: Phenolphthalein can be used to create colored bubbles.

• Laxative: Phenolphthalein has been used as a laxative, but its use has mainly been discontinued due to potential carcinogenicity.

Frequently Asked Questions on Phenolphthalein

What is Phenolphthalein Used for?

Phenolphthalein is used as a pH indicator in laboratory settings and is commonly employed in acid-base titrations.

How does Phenolphthalein Change Color in Acid-Base Titration?

Phenolphthalein turns colorless in acidic solutions and pink in basic solutions during acid-base titration, making it a visual indicator of the endpoint.

What is Clinical Use of Phenolphthalein?

In clinical practice, Phenolphthalein was once used as a laxative, but its use has declined due to safety concerns and potential carcinogenicity.

What is Kastle-Meyer Test?

Kastle-Meyer test is a forensic test used to detect the presence of blood by using Phenolphthalein as an indicator.

What is pH Range of Phenolphthalein?

Phenolphthalein has a pH range of approximately 8.2 to 10.0, making it suitable for indicating the endpoint of titrations involving strong bases and weak acids.

What is Colour of Phenolphthalein?

Colour of Phenolphthalein in basic soluion is pink and in case of acidic solution phenolphthalein is colorless.

Is Phenolphthalein harmful for Health?

Exposure to phenolphthalein causes multiple carcinogenic effects, including neoplasm in kidney, adrenal medulla, hematopoietic system, and ovary in rats.

Is Phenolphthalein Acidic or Basic?

Phenolphthalein, is a weak acid with chemical formula of C₂₀H₁₄O₄