Which components comprise a buffer system that resists changes in pH?

Which components comprise a buffer system that resists changes in pH?

• A. A strong acid and a strong base
• B. A metal ion and water
• C. A polysaccharide and a lipid
• D. A weak acid and its conjugate base (buffer pair)

Answer: (D)

Buffer systems resist pH changes because they rely on a weak acid and its conjugate base (or a weak base and its conjugate acid). This pair can neutralize added strong acids by accepting H+ (converting base form to the acid form) and can neutralize added strong bases by donating H+ (converting acid form to the base form). The result is a solution whose pH stays near the acid’s dissociation constant (pKa) since the ratio of conjugate base to weak acid controls the pH. For example, in the blood the bicarbonate system (a weak acid and its conjugate base) buffers against shifts in pH, keeping it around a narrow range essential for enzyme activity. Other combinations, like a strong acid with a strong base, don’t provide buffering because they produce large pH swings rather than dampening them. A metal ion with water and a polysaccharide with a lipid are not designed to resist pH changes in this way.

Buffer systems resist pH changes because they rely on a weak acid and its conjugate base (or a weak base and its conjugate acid). This pair can neutralize added strong acids by accepting H+ (converting base form to the acid form) and can neutralize added strong bases by donating H+ (converting acid form to the base form). The result is a solution whose pH stays near the acid’s dissociation constant (pKa) since the ratio of conjugate base to weak acid controls the pH.

For example, in the blood the bicarbonate system (a weak acid and its conjugate base) buffers against shifts in pH, keeping it around a narrow range essential for enzyme activity. Other combinations, like a strong acid with a strong base, don’t provide buffering because they produce large pH swings rather than dampening them. A metal ion with water and a polysaccharide with a lipid are not designed to resist pH changes in this way.