Question

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

Answer 1

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.