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

1 Answer
anor277
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:

#HCl(g) + H_2O(l) rightleftharpoons H_3O^+ + Cl^-#

#HCl# shares this property with its lower congeners, #HBr#, and #HI#. #HF#, however, is not a strong acid in water, and salts of #NaF# 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 #HF#; the entropy effect is probably the more significant.

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