[tex]HF \rightleftharpoons H^{+} + F^{-}\\[/tex]
We have 1.5 M HF in the beginning and 0 M [tex]H^{+}[/tex] and [tex]F^{-}[/tex]
We know that there's gonna be a decrease of x M on [tex]HF[/tex] and an increase of x M on [tex]H^{+}[/tex] and [tex]F^{-}[/tex].
We also find in chemistry tables that [tex]K_{a}(HF) = 6.8 \cdot 10^{-4}[/tex]
[tex]K_a = \frac{[H^+] \cdot [F^-]}{[HF]}\\6.8 \cdot 10^{-4} = \frac{x \cdot x}{1.5 - x} \\6.8 \cdot 10^{-4} = \frac{x^2}{1.5}\\6.8 \cdot 10^{-4} \cdot 1.5 = x^2\\x^2 = 1.02 \cdot 10^{-3}\\x = 0.0319\\pH = -\log{0.0319}\\pH = 1.5[/tex]
