bufferssolutions

Buffer solutions are solutions that resist changes in pH upon addition of small amounts of acid or base or upon dilution. They consist of a weak acid and its conjugate base, or a weak base and its conjugate acid. They maintain a relatively constant pH within a certain range, making them essential in chemical reactions and biological systems where pH must be controlled.

Principle: when a strong acid is added, the conjugate base component neutralizes part of the added H+. When a strong base is added, the weak acid component neutralizes OH-. The capacity depends on the total amount of buffering species.

Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]) for acid buffers. Buffer ranges are typically within about one pH unit of the pKa.

Preparation and selection: choose a weak acid with a pKa near the desired pH, mix it with its salt to obtain the required ratio. Adjust total concentration to set buffer capacity. Temperature and ionic strength affect the pKa and capacity.

Common examples: acetic acid/acetate, ammonium/ammonia systems, phosphate buffers (monobasic/dibasic), citrate buffers, and Good's buffers.

Applications: biology (blood, intracellular environments), medicine (drug formulations), analytical chemistry, fermentation, and laboratory assays. They are also used in food science and industrial processes.

Limitations: effective range is limited; each buffer has finite capacity that is exceeded with large additions of acid or base; dilution reduces capacity; extreme pH or high temperature can shift pKa and compromise performance.