Synthesis of Hydrogen Fluoride
In desperation, for some unknown reason, I need 15% aqueous $\ce{HF}$. What do I really need? A weak solution of $\ce{H+}$, say about pH 2. And a solution of fluoride ions to wreak havoc on some unsuspecting metal or glass(Ooops, I may have given away the secret). 

My subconscious suggests that I could get them from two different sources, like $\ce{NaF}$ and $\ce{HCl}$. Yeah, that'll work. 

Maybe. Maybe even with $\ce{CaF2}$(The use of $\ce{H2SO4}$ with the calcium salt suggests the reason was to precipitate the $\ce{CaSO4}$ and flash off the $\ce{HF}$, thereby separating, not just generating, the $\ce{HF}$).