> See also: > - [[Solutions & Concentrations]] https://www.jove.com/science-education/v/11153/concepts/buffers # Buffer Solutions The **buffer capacity** is the amount of acid or base that can be added to a given volume of a buffer solution *before the pH changes significantly* (typically by more than 1 unit). A buffer is essentially a *weak acid/base* and it's corresponding conjugate acid/base A weak acid or a weak base ### Effectiveness of Buffers Different buffers can only effectively stabilize the pH value for specific ranges based on their pKa. - In biological research labs, **"Tris"** is a common buffer as it operates at a pH of 8 (similar to the pH of cellular environments) > [!check]- Desired Buffer Properties > - Water Soluble > - High Purity at Low Cost > - Stable Over Time > - **Buffer Calculators** - [Sigma Aldrich](https://www.sigmaaldrich.com/US/en/support/calculators-and-apps/buffer-calculator) - [Science Gateway](https://www.sciencegateway.org/tools/buffer.htm) ## The Henderson-Hasselbalch Equation The following equation can be derived from the [[Chemical Equilibria#ionization constants|acid-ionization constant]]: > [!abstract] The Henderson-Hasselbalch Equation > $pH = pK_a + \log \frac{[A^-]}{[HA]}$ > > $pK_a$ = Negative logarithm of the ionization constant of the weak acid ($pK_a = - \log K_a$) > $[A^-]$ = Concentration of acid Only useful for weak acids/weak bases? This equation is derived from the standard equilibrium constant monoprotic vs polyprotic buffers? its important to remember that at the end of the day the pH is the concentration of hydronium ions - the pKa value is **experimentally calculated** - the henderson hasselbalch equation essentially lets us cancel out the ratio of A-:HA and be left with only the concentration of hydronium ions (originating from the pKa) -