Acetic acid (CH3COOH) is a weak acid, meaning it tends to donate a proton (H+) but does so to a limited extent. Hydrofluoric acid (HF) is a stronger acid compared to acetic acid. When acetic acid is dissolved in HF, it can undergo a proton transfer reaction in which HF donates a proton to acetic acid. This reaction can be represented as follows:
CH3COOH + HF ⟶ CH3COO- + H2F+
In this reaction, acetic acid accepts a proton from HF, resulting in the formation of the acetate ion (CH3COO-) and the hydronium fluoride ion (H2F+). The acetate ion, which is the conjugate base of acetic acid, is relatively stable.
The reason acetic acid acts as a base in this particular context is that HF is a stronger acid than acetic acid. In the presence of a stronger acid like HF, acetic acid can accept a proton, demonstrating its basic behavior.
It is important to note that the strength of an acid or base is relative to the particular chemical environment in which it is found. Acetic acid behaves as a weak acid in most cases, but in the presence of stronger acids, it can act as a base.