Acidity of hydrochloric acid in acetic acid A question asked to find the $\mathrm pK_\mathrm a$ of $\ce{HCl}$ in acetic acid. The equation of $\ce{HCl}$ disassociating in water is: $$\ce{HCl + CH3COOH \leftrightharpoons CH3COOH2+ + Cl-}$$ I predicted that the $\mathrm pK_\mathrm a$ should be higher  as acetic acid is a weaker base than water so it would be less willing to accept a proton from a $\ce{HCl}$. 

However when I finally calculated the $\mathrm pK_\mathrm a$, I got 8.56. This was much higher than I expected. Also doesn't this imply that $\ce{Cl-}$ is stronger as a base than $\ce{HCl}$ is as an acid in acetic acid, which doesn't sound right. 

So I am asking if this value totally wrong or is it actually quite reasonable?
So basically I am asking, is this value totally wrong or is it actually quite reasonable?


It's quite reasonable. Compare to page 32 of this reference.


  This was much higher than I expected. Also doesn't this imply that
  Cl− is stronger as a base than HCl is as an acid in acetic acid, which doesn't sound right. 


To answer whether Cl- is a stronger base than HCl is an acid, you need to know the self-dissociation constant of acetic acid, the equivalent of Kw for water. It is about $10^{-10}$. So whereas the middle of the pH scale is thought of as 7, the middle for acetic acid would be 5. So, yes, Cl- is a stronger base than HCl is an acid in acetic acid.