We are asked to provide the net ionic equation for the reaction of HF (aq) and NaF (aq). HF is a weak acid and is in the following equilibrium:
HF (aq) ⇄ H⁺ (aq) + F⁻ (aq)
Meanwhile, NaF (aq) is an ionic compound that will dissociate completely in aqueous solutions:
NaF (aq) → Na⁺ (aq) + F⁻ (aq)
We can combine the ionic species with HF, as we are told to show F⁻ as a reactant:
HF (aq) + Na⁺ (aq) + F⁻ (aq) → HF (aq) + Na⁺ (aq) + F⁻ (aq)
We can eliminate the spectator ions, which in this case are Na⁺ ions, and this leaves us with the net ionic equation involving F⁻:
HF (aq) + F⁻ (aq) → HF (aq) + F⁻ (aq)
In this instance, the proton is just transferred between F⁻ ions and the end result is the formation of more HF, so there is no net reaction taking place.
