Question

The odor of vinegar is due to the presence of acetic acid, CH₃CO₂H, a weak acid. List, in order of descending concentration, all of the ionic and molecular species present in a 1-M aqueous solution of this acid.

a) CH₃CO₂H, H₃O⁺, CH₃CO₂⁻, H₂O
b) H₃O⁺, CH₃CO₂H, CH₃CO₂⁻, H₂O
c) CH₃CO₂⁻, H₃O⁺, CH₃CO₂H, H₂O
d) H₂O, CH₃CO₂⁻, H₃O⁺, CH₃CO₂H

Answer 1

In a 1-M aqueous solution of acetic acid, the concentration of undissociated acetic acid molecules is the highest, with water being the solvent present in large excess, followed by the hydronium ions, and lastly, the acetate ions.

Step-by-step explanation:

The odor of vinegar is attributed to acetic acid (CH₃CO₂H), which is a weak acid. When acetic acid is dissolved in water, it partially dissociates into ions.

However, since it's a weak acid, the concentration of undissociated acetic acid molecules will be highest, followed by water (the solvent, which is always present in large excess), the hydronium ions (H₃O⁺), and then the acetate ions (CH₃CO₂⁻). Therefore, the correct order of descending concentration of the species in a 1-M aqueous solution of acetic acid will be:

1. CH₃CO₂H
2. H₂O
3. H₃O⁺
4. CH₃CO₂⁻