Understanding the Reaction of Litmus with Ethanol

The question asks about the action of litmus on ethanol. To answer this, we need to understand what litmus is and the chemical properties of ethanol, specifically its nature as an acid, base, or neutral substance when tested with an indicator like litmus.

What is Litmus?

Litmus is a natural dye extracted from lichens. It is commonly used as a pH indicator to test whether a solution is acidic or alkaline (basic). Litmus paper, which is filter paper treated with litmus, comes in two main forms: blue litmus paper and red litmus paper.

Essentially, an acidic solution will turn blue litmus red, a basic solution will turn red litmus blue, and a neutral solution will not change the color of either blue or red litmus.

Properties of Ethanol ($\text{C}_2\text{H}_5\text{OH}$)

Ethanol is an alcohol. Alcohols contain a hydroxyl ($\text{-OH}$) group. While the $\text{-OH}$ group in organic molecules can sometimes behave like the $\text{-OH}$ in inorganic bases, alcohols generally do not dissociate in water to produce hydroxide ions ($\text{OH}^-$) in the way strong bases do. In fact, the hydrogen atom in the $\text{-OH}$ group of alcohols can, under certain conditions, be donated, showing very weak acidic character.

However, ethanol is a very weak acid, much weaker than water. Its ability to donate a proton is minimal in aqueous solution. Pure ethanol has a $\text{pH}$ very close to 7. When dissolved in water, its $\text{pH}$ is typically slightly below 7 due to the presence of dissolved carbon dioxide from the air forming carbonic acid, or its own very slight self-ionization. But this slight acidity is not strong enough to cause a visible color change in litmus paper, which requires a more significant change in $\text{pH}$ to shift colors.

Ethanol does not act as a base in aqueous solutions and will not accept protons to form $\text{OH}^-$ ions or donate electrons significantly to be considered a base towards indicators like litmus.

Action of Ethanol on Litmus Paper

Given that ethanol is practically neutral with respect to its action on common indicators like litmus paper, we can predict its effect:

• If blue litmus paper is dipped in ethanol, it will remain blue.
• If red litmus paper is dipped in ethanol, it will remain red.

This indicates that ethanol does not have strong enough acidic or basic properties to cause the characteristic color changes associated with acids and bases when using litmus paper.

Analyzing the Provided Options

Let's look at the given options in light of our understanding:

1. Litmus is neutral towards ethanol

   This statement suggests that ethanol does not cause a color change in litmus, implying ethanol behaves as a neutral substance relative to the sensitivity of litmus. This aligns with our understanding of ethanol's properties and its action on litmus.

2. Ethanol turns blue litmus to red; confirming acidic nature of ethanol

   While ethanol does have a very weak acidic character, it is not strong enough to turn blue litmus red. Litmus is not sensitive enough to detect the extremely weak acidity of ethanol.

3. Ethanol turns red litmus to blue; confirming basic nature of ethanol

   Ethanol is not basic and does not turn red litmus blue. This statement is incorrect.

4. Ethanol decolorizes litmus through bleaching action

   Ethanol does not possess bleaching properties and does not decolorize litmus paper. This statement is incorrect.

Based on the analysis, the statement that litmus is neutral towards ethanol accurately describes the observed action.

Conclusion on Ethanol Litmus Reaction

Ethanol, a common alcohol, is considered neutral when tested with litmus paper. Its very weak acidic character is insufficient to cause the color change required for litmus to indicate acidity. Therefore, neither red nor blue litmus paper changes color when placed in ethanol.

Revision Table: Litmus Test Summary

Additional Information: Acid-Base Strength and Indicators

The effectiveness of an indicator like litmus depends on the strength of the acid or base being tested. Litmus changes color over a $\text{pH}$ range of approximately 4.5 to 8.3. Blue litmus turns red below $\text{pH}$ 4.5, and red litmus turns blue above $\text{pH}$ 8.3. In the $\text{pH}$ range between 4.5 and 8.3, litmus shows intermediate colors or doesn't give a sharp change.

Since pure ethanol has a $\text{pH}$ very close to 7 (neutral), and even slightly impure ethanol typically stays within the neutral range or very weakly acidic range that falls within the insensitive $\text{pH}$ window for litmus, it does not cause a visible color change. Stronger acids (like $\text{HCl}$) or strong bases (like $\text{NaOH}$) are needed to produce the significant $\text{pH}$ shifts required to change the color of litmus paper.