Question

Why does pure acetic acid not turn blue litmus to red?

Answer 1

When acids are placed in an aqueous medium or are interacted with basic substances, they tend to release a hydrogen atom from the molecule of the acid. The degree and ease to which this hydrogen atom gets released from the molecule of the acid determines the acidity of the acid

Complete step by step answer:
The higher the dissociation of the hydrogen atom, the higher is the acidity of that particular acid.
Acetic acid is a very weak acid. In pure acetic acid, they form intermolecular hydrogen bonding. Therefore, no dissociation occurs in pure acetic acid. Which results in the release of hydrogen ion is not possible in pure acetic acid. As a result, pure acetic acid does not show acidity.
Acids change the color of blue litmus into red. But as pure acetic acid has no acidity, it does not turn blue litmus to red.

Additional information:
When comparing the acidity of compounds using their molecular structures, we must understand that the more stable molecules tend to release their hydrogen atoms with much more ease as compared to non – stable atoms. Hence, the acidity of stable molecules is higher than non – stable molecules.
The given options to us are acetic acid, formic acid, and carbonic acid. The molecular structures of these compounds can be drawn as follows:
1.Acetic acid:

2.Formic acid:

3.Carbonic acid:

Upon observation, we can see that all these compounds do not have any resonance structures, and hence are relatively less stable. Hence, all these compounds are weak acids.
Note: This property of acidity is mathematically measured using a method known as the pH scale. Depending on the degree of dissociation of hydrogen atoms, the acidity of the substance is calculated. On a scale of 1 to 14, substances with a pH value between 1 to 7 are known as acids, with 1 being the most acidic and 7 being the least acidic.