Buffer (chemistry)

Article

August 19, 2022

In chemistry, a buffer or an acidity regulator is an aqueous solution of two substances that are in a certain equilibrium and adopt a certain pH ( acidity). When diluting, adding an acid or a base, this pH will remain almost constant. The disturbance of the equilibrium and the acidity is thus 'buffered'. Buffer solutions always consist of an acid/base couple; either an acid and the salt of its conjugate base or a base and the salt of its conjugate acid. Both are always weak acids or bases, so they will react incompletely. The reaction equation between the acid and the base can be given as: huh z ( a q ) z ( a q ) + huh ( a q ) + {\displaystyle \mathrm {HZ_{(aq)}\rightleftarrows Z_{(aq)}^{-}+H_{(aq)}^{+}} } To what extent this reaction proceeds is given by the Kz value or acid constant: k z [ huh + ] [ z ] [ huh z ] {\displaystyle \mathrm {K_{z}{\frac {[H^{+}][Z^{-}]}{[HZ]}}} }

Comments

The occurring reactions of the acid and base in water respectively are: 1. huh z + huh 2 O z + huh 3 O + {\displaystyle \mathrm {HZ+H_{2}O\rightleftarrows Z^{-}+H_{3}O^{+}} } 2. z + huh 2 O huh z + O huh {\displaystyle \mathrm {Z^{-}+H_{2}O\rightleftarrows HZ+OH^{-}} } There is also a continuous equilibrium between the number of hydroxide and hydroxonium ions in the water: 2 huh 2 O huh 3 O + + O huh {\displaystyle \mathrm {2H_{2}O\rightleftarrows H_{3}O^{+}+OH^{-}} }

pH

The pH of a buffer mixture can be calculated using the Henderson-Hasselbalch equation: p huh p k a