Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

Eosine used to detect the end point of precipitation titration by adsorption is called (a) absorption indicator (b) adsorption indicator (c) normal indicator (d) chemical indicator

Step-by-Step Solution

Answer

(b) adsorption indicator

Step 1: Understand the Term "Adsorption"

The term "adsorption" refers to the process where molecules adhere to the surface of a solid or liquid. In titration scenarios, indicators that work through adsorption change color when they attach to a specific point on the precipitate or a surface.

Step 2: Identify the Purpose of Eosine

Eosine is used in chemical processes to indicate an endpoint, specifically in precipitation titrations. This particular application relies on its ability to adhere to surfaces during these reactions.

Step 3: Select the Correct Choice

Considering the properties of eosine and its role in precipitation titrations, it fits the definition of an adsorption indicator. It specifically changes color when adsorbed, signifying that it should be classified accordingly.

Key Concepts

Adsorption Process

The adsorption process is a fascinating chemical phenomenon where particles, such as atoms, ions, or molecules, adhere to the surface of a material. This surface could be a solid or a liquid. In the context of chemistry and titrations, adsorption is crucial because it allows certain indicators to function effectively.
Through the adsorption process, we can observe phenomena such as:

• Surface attraction, where molecules are drawn to the exterior layer of a material.
• Color change, often seen in chemical indicators that rely on adsorption to show a visual cue at the endpoint of chemical reactions.

For instance, in precipitation titrations, the adsorbed indicator can show a distinct color change. Indicators like eosine stick to the precipitate, enabling determination of the titration endpoint. This aspect of adsorption is key in various analytical chemistry applications.

Precipitation Titration

Precipitation titration is a type of titration that depends on the formation of a solid precipitate during the chemical reaction. The endpoint of such titrations is identified when the amount of titrant added is sufficient to complete the precipitation reaction.

This method offers unique advantages:

• Allows identification through visual changes when the solution reaches its endpoint.
• Useful in determining the concentration of ions in a solution by producing an insoluble solid.

The process is enhanced when combined with an adsorption indicator. This is because such indicators clearly highlight the end of the titration by attaching to the newly formed precipitate and changing color. This direct visual cue is especially useful for accuracy in quantitative analyses.

Indicator Choice

Choosing the right indicator in titrations is crucial, as its role is to signal the endpoint by changing color. Indicators must be matched to the type of titration for accurate results. In precipitation titrations, adsorption indicators like eosine are particularly effective.

Why adsorptive indicators work well:

• They attach to the surface of the precipitate, creating a strong color change.
• They provide visual confirmation of the endpoint accurately and efficiently.

When selecting an indicator, one must consider:

• The specific reaction's nature and what precipitate is expected.
• The visibility of the indicator change to ensure clear detection of the endpoint.

Adsorption indicators are chosen for their definitive color shifts, which are unmistakable at the reaction's endpoint, making them indispensable in efficient and accurate titrations.