Ammoniakbuffers

Ammoniakbuffers (ammonia buffers) are buffer solutions composed of ammonia (NH3) and its conjugate acid ammonium (NH4+). They resist changes in pH when small amounts of acid or base are added, within a limited pH range determined by the NH3/NH4+ system.

Chemistry: The buffering action follows the equilibrium NH3 + H2O ⇌ NH4+ + OH−. The pH can be described by Henderson–Hasselbalch: pH = pKa(NH4+) + log([NH3]/[NH4+]). At 25°C, the pKa of NH4+ is about 9.25, so these buffers function mainly in the alkaline range, typically around pH 8.5 to 10.5 depending on the ratios of base to conjugate acid. Buffer capacity increases with the total concentration of ammonia species.

Preparation and components: A buffer is formed from a source of NH3 (aqueous ammonia) and a source of NH4+, commonly ammonium chloride (NH4Cl). By adjusting the ratio of NH3 to NH4+ and the total concentration, the desired pH and buffer strength can be set. Temperature affects the pKa slightly, with pH values shifting modestly as temperature changes.

Applications: Ammonia buffers are used in laboratory settings to maintain alkaline conditions for certain enzymatic reactions, protein assays, and electrophoretic methods that require pH above 9. They also appear in environmental and industrial contexts where stabilization of alkaline pH is needed.

Safety: Ammonia is caustic; handle aqueous ammonia solutions with adequate ventilation. Ammonium salts are less volatile but should be used following standard chemical-safety guidelines.