Theories Of Acid Base Indicators | Ostwald's Theory | Quinonoid Theory | Pharmaceutical Analysis

Summary

This video explains the role of pH indicators, focusing on two key theories: Oswald's Theory and Konno's Theory. Oswald's Theory describes how indicators like phenolphthalein change color in response to pH, turning pink as the solution becomes basic. Konno's Theory further elaborates on the structural changes in indicators, with examples like methyl orange shifting from red in acidic conditions to yellow in basic environments. The video provides an in-depth understanding of how indicators function, their color changes, and the chemistry behind it all, with practical examples to aid learning.

Takeaways

• 😀 Indicators change color in response to the pH of a solution, shifting from one form to another depending on whether the solution is acidic or basic.
• 😀 In an acidic solution, phenolphthalein remains colorless as it is in its non-ionized form.
• 😀 As the solution becomes basic, phenolphthalein dissociates and turns pink due to its interaction with hydroxide ions (OH⁻).
• 😀 The Oswald Theory explains that phenolphthalein’s color change is due to structural changes as the pH of the solution shifts.
• 😀 The Konot Theory suggests that indicators exist in two forms: benzinoid and quinoid, with each showing different colors depending on the pH of the solution.
• 😀 In the benzinoid form, indicators like phenolphthalein are colorless in acidic solutions.
• 😀 When the solution turns basic, phenolphthalein shifts to the quinoid form, resulting in a pink color.
• 😀 The color change of an indicator occurs because its molecular structure changes when it reacts with the environment (acidic or basic).
• 😀 Methyl orange is red in acidic conditions (quinoid form) and yellow in basic conditions (benzinoid form).
• 😀 The behavior of indicators is explained by their structural transformation, which leads to different colors under acidic or basic conditions.

Q & A

What is the Oswald Theory about?

The Oswald Theory explains how an indicator, like phenolphthalein, changes color in response to pH changes in a solution. When the solution becomes basic, phenolphthalein dissociates, releasing a negative ion that turns the solution pink.

How does phenolphthalein behave in acidic and basic solutions according to the Oswald Theory?

In an acidic solution, phenolphthalein remains colorless. When the solution becomes basic, phenolphthalein dissociates into its ionized form, turning the solution pink.

What is the role of dissociation in the color change of phenolphthalein?

Dissociation is the key factor in the color change. When phenolphthalein dissociates in a basic solution, it forms a negative ion that causes the solution to turn pink.

What are the two forms of indicators according to the Konnect Theory?

The Konnect Theory proposes that indicators exist in two forms: the benzinoid form and the quinonoid form. The benzinoid form is colorless in acidic solutions, while the quinonoid form is colored, typically pink, in basic solutions.

What happens to the indicator when it changes from the benzinoid form to the quinonoid form?

When an indicator changes from the benzinoid form to the quinonoid form, the color of the solution changes. The benzinoid form is colorless, but the quinonoid form shows a color, such as pink, in basic conditions.

How does methyl orange behave in acidic and basic solutions?

Methyl orange shows a red color in acidic solutions and turns yellow in basic solutions, demonstrating a change in color based on the pH level of the solution.

What is the significance of the structural change in indicators according to the Konnect Theory?

The structural change of indicators is crucial for the color change. When an indicator shifts between its benzinoid and quinonoid forms due to the change in pH, the color of the solution changes accordingly, with each form having a distinct color.

What is the color change observed when phenolphthalein is placed in an acidic solution?

In an acidic solution, phenolphthalein remains colorless as it is in the benzinoid form, which is colorless.

Why does phenolphthalein change color in a basic solution?

In a basic solution, phenolphthalein shifts to its quinonoid form, which is pink in color, causing the solution to turn pink.

What is the difference between the Oswald Theory and the Konnect Theory regarding the color change of indicators?

The Oswald Theory focuses on the dissociation of the indicator in basic solutions, whereas the Konnect Theory emphasizes the change in the chemical structure of the indicator between the benzinoid and quinonoid forms, resulting in color changes.