The pink colour of phenolphthalein, in alkaline medium, is due toa)OH⁻ ionb)neutral formc)positive iond)negative ionCorrect answer is option 'D'. Can you explain this answer?

Question

The pink colour of phenolphthalein, in alkaline medium, is due toa)OH&#8315; ionb)neutral formc)positive iond)negative ionCorrect answer is option 'D'. Can you explain this answer?

Answer

The pink colour is because of high concentration o

f In- ions in the solution.

Answer

Phenolphthalein (HIn) is weakly acidic in nature. And in aqueous solution, it dissociates into and ions. The pink colour of the solution is due to the concentration of ions in the solution. Under acidic conditions, the concentration of in the solution is very low and concentration of is high, hence it is colourless.

Answer

Phenolphthaleins color change happens through a process called ionization. Ionization occurs when a molecule gains or loses electrons, giving the molecule a negative or positive electric charge. Ionized molecules attract other molecules with the opposite charge and repel those with the same charge. With phenolphtalein, this also affects the molecules shape. The combination of shape and electric charge determine how a molecule responds to light. Normally, phenolphtalein is clear because all colors of light pass through it. When exposed to alkaline solutions, it begins to block the blue colors of the spectrum, which turns the light pinkish. The stronger the alkaline solution is, the more the phenolphthalein molecule changes and the darker the its pink hue will be.

Answer

Explanation:

Phenolphthalein is a pH indicator that changes color depending on the acidity or alkalinity of a solution. In acidic solutions, phenolphthalein is colorless, but in alkaline solutions, it turns pink. The pink color in alkaline medium is due to the presence of the negative ion of phenolphthalein.

Phenolphthalein undergoes a chemical reaction in the presence of hydroxide ions (OH-) that are present in alkaline solutions. The reaction involves the deprotonation of phenolphthalein, resulting in the formation of a negative ion.

Explanation of the reaction:

1. In the neutral form of phenolphthalein, there are two phenol groups (C6H4OH) attached to a central carbon atom (C).

2. In an alkaline medium, hydroxide ions (OH-) react with the phenolphthalein molecule. The hydroxide ion abstracts a hydrogen ion (H+) from one of the phenol groups.

3. This deprotonation reaction results in the formation of a negative ion, which is responsible for the pink color. The negative ion has a double negative charge and is represented as (C20H13O4-) in the case of phenolphthalein.

Color change mechanism:

The pink color arises due to the conjugation present in the negative ion of phenolphthalein. Conjugation is the delocalization of electrons across multiple bonds. In the case of phenolphthalein, the negative charge is delocalized across the entire molecule, creating a system of alternating single and double bonds.

This conjugated system of bonds absorbs light in the visible region of the electromagnetic spectrum. The absorbed light corresponds to wavelengths in the green part of the spectrum, while the complementary color, pink, is transmitted or reflected.

Therefore, the pink color observed in alkaline medium is due to the presence of the negative ion of phenolphthalein, which is formed by the deprotonation reaction with hydroxide ions (OH-).

Answer

The pink colour of phenolphthalein is dur to double negative ion which is due to forming of carboxylate ion and the leaving phenolate ion....

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