# Is hydrochloric acid (HCl) a strong acid or a weak acid? Does it dissociate completely or partially?

Aug 10, 2016

Hydrogen chloride is a strong acid as acids go. What does this mean?

#### Explanation:

In water the following equilibrium lies almost quantitatively to the right:

$H C l \left(g\right) + {H}_{2} O \left(l\right) r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + C {l}^{-}$

$H C l$ shares this property with its lower congeners, $H B r$, and $H I$. $H F$, however, is not a strong acid in water, and salts of $N a F$ would give a slightly basic solution. Why?

The fluorine atom is much smaller than chlorine and bromine, and the resultant $H - X$ bonds are weaker than for $X = F$. The ${F}^{-}$ is smaller and more polarizing in aqueous solution, and formation of this ion is also entropically disfavoured. Bot entropy and enthalpy combine to reduce the acidity of $H F$; the entropy effect is probably the more significant.