What term describes a solution that resists changes in pH when acids or bases are added?

• A. Acid
• B. Buffer
• C. Base
• D. Solvent

Answer: (B)

A buffer is a solution that resists changes in pH when acids or bases are added. It works because it contains a weak acid and its conjugate base (or a weak base and its conjugate acid). When extra H+ is introduced, the conjugate base form neutralizes the protons, forming the weak acid and preventing a large drop in pH. When extra OH- is added, the weak acid donates protons to neutralize it, forming water and the conjugate base, which keeps the pH from rising much. The buffering effect is strongest near the pKa of the buffer pair, and the capacity increases with higher concentrations of the buffering components. Real-world examples include the bicarbonate/carbonic acid system in blood and phosphate buffers in cells or acetate buffers in the lab. An acid alone lowers pH, a base alone raises pH, and a solvent is just the medium. So the term that describes a solution that resists changes in pH is a buffer.