Question

The colour change of an acid-base indicator is due to the formation of (1) Benzenoid structure (2) Quinonoid structure (3) Ionic structure (4) Covalent bond

Short answer

Quinonoid structure

Step-by-step solution

Understand Acid-Base Indicators

Acid-base indicators are substances that change color when they are exposed to different pH levels. They typically do this by existing in different molecular forms at different pH levels.

Identify the Two Main Structures in Indicators

The main forms acid-base indicators can exist in are benzenoid and quinonoid structures. These structures correspond to different pH levels.

Determine the Structure Responsible for Color Change

The color change in acid-base indicators is primarily due to the transition between benzenoid and quinonoid forms. The specific structure responsible is the quinonoid structure.

Analyze Other Options

Benzenoid structures, ionic structures, and covalent bonds also play roles in chemistry but are not responsible for the color change in acid-base indicators. Confirming quinonoid structure is the correct answer ensures the process causing the color change is understood.

Key concepts

benzenoid structure

In the world of chemistry, understanding the benzenoid structure is essential, especially when discussing acid-base indicators.
The benzenoid structure is a type of molecular structure characterized by a benzene ring.
Benzene rings consist of six carbon atoms arranged in a hexagonal ring, with alternating double bonds.
This structure is highly stable and contributes to the unique properties of compounds like those used in acid-base indicators.
The stability of the benzenoid structure comes from the resonance, where the electrons are delocalized over the ring.
This delocalization stabilizes the molecule and makes it less reactive under normal conditions.
In the context of acid-base indicators, the benzenoid form usually corresponds to one of the color states of the indicator, depending on the pH of the solution it is in.
However, the benzenoid structure itself is not responsible for the color change of the indicator.

quinonoid structure

Moving on to another important structure for acid-base indicators, we have the quinonoid structure.
This structure forms when a molecule rearranges itself under different pH conditions.
The quinonoid structure is less stable than the benzenoid structure and is often associated with a different color in acid-base indicators.
In the quinonoid form, the electrons are more localized compared to the delocalized electrons in the benzenoid structure, leading to different light absorption properties.
This change in light absorption is what causes the visible color change that makes acid-base indicators so useful in chemistry.
When the pH of the environment changes, the indicator can switch between the benzenoid and quinonoid forms, resulting in a noticeable color change.
Thus, the quinonoid structure is directly responsible for the color change seen in acid-base indicators, making it a crucial concept to understand.

color change

One of the most fascinating aspects of acid-base indicators is their ability to change color.
When you add an indicator to a solution, it can reveal the pH of the solution based on the color it turns.
This color change occurs due to the structural transitions between the benzenoid and quinonoid forms of the molecule.
In acidic conditions, the indicator may exist in one form, displaying a specific color, while in basic conditions, it may shift to another form, displaying a different color.
The shift between these two forms involves changes at the molecular level, specifically in the electron configuration and the structure of the molecule.
By understanding the underlying structures and the principles of how they interact with light, you can see why color change occurs.
It's not just a simple transition; it's a glimpse into the dynamic world of molecular chemistry that makes acid-base indicators valuable tools for both educational and practical purposes.