Question

Is HCl a buffer?

Answer 1

Hydrochloric Acid($\mathbf{HCl}$) is not a buffer, because it is a strong acid and dissociates completely in an aqueous solution.

1. However, when hydrochloric acid is combined with a salt of a weak acid in the appropriate proportion it can form a buffer solution.
2. Hydrochloric acid ($\mathbf{HCl}$) dissolves in water $\mathrm{H}\mathrm{C}\mathrm{l}\to {{\mathrm{H}}^{+}}^{}(\mathrm{a}\mathrm{q})+\mathrm{C}{{\mathrm{l}}^{-}}^{}(\mathrm{a}\mathrm{q})$
3. For example, when sodium acetate is present in excess, hydrochloric acid forms an acetate buffer containing the acetate ion and acetic acid as an equilibrium solution.$$\begin{gathered} \mathrm{HCl}+2{\mathrm{CH}}_3{\mathrm{COONa}}^{-}>{\mathrm{CH}}_3{\mathrm{COO}}^{-}+{\mathrm{CH}}_3\mathrm{COOH}+2{\mathrm{Na}}^{+}+{\mathrm{Cl}}^{-} \\ {\mathrm{CH}}_3\mathrm{COOH}\leftarrow >{\mathrm{H}}^{+}+{\mathrm{CH}}_3{\mathrm{COO}}^{-} \end{gathered}$$
4. It prepares the acetic acid for the buffer in situ.
5. So, if we made a solution with one mole of $\mathbf{HCl}$and two moles of sodium acetate in one liter of water, the finished product would be like mixing 500 ml of 2M acetic acid and 500 ml of 2M sodium acetate.
6. (The extra $\mathbf{NaCl}$ that is formed can be disregarded because it does not affect $\mathbf{pH}$.) With this mixture, an acetate buffer solution with a $\mathbf{pH}$ of approximately 4.62 will be produced.

Hence, $\mathbf{HCl}$is not a buffer.