Respuesta :
Answer:
Explanation:
Buffer solutions are solutions capable of maintaining their pH at approximately constant values when small amounts of acid or base are added.
A buffer solution is characterized by simultaneously containing a weak species and its conjugate pair. In other words, it has a weak acid and a salt of the same acid from a strong base or, a base and a salt of this base from a strong acid.
Two examples are:
- Mixture of acetic acid and sodium acetate
- Ammonium Hydroxide and Ammonium Chloride
Given that the buffer solution is a mixture of weak acid with a salt of the same acid from a strong base, the acid will be partially dissociated according to the equation:
HA ⇔ [tex]H^{+} + A^{-}[/tex]
Applying the Law of Mass Action (which establishes the relationship between the masses of reagents and products in a chemical equilibrium at a given temperature) and taking into account the dissociation constant([tex]Ka=\frac{[A^{-}]*[H^{+}] }{[HA]}[/tex]) is obtained the following expression:
[tex]pH=pKa+log\frac{[A^{-} ]}{[HA]}[/tex]
Where pKa represents the potential value of the acid acid constant of the weak acid, [tex][A^{-} ][/tex] is the common anion concentration, equivalent to salt and [HA] indicates weak acid concentration which is part of the buffer solution. Consequently, the above equation can be rewritten as follows:
[tex]pH=pKa+log\frac{salt}{acid}[/tex]
According to this equation, the pH of a solution buffer, depends on two factors:
a) The pKa value of the weak acid
b) The proportions between salt and acid concentrations
In summary, the presence of the conjugate pair causes the weak species to dissociate to a lesser extent and the presence of the weak species causes the conjugate pair to hydrolyze less.