What is pH, and how does a buffer work to resist changes in pH?

What is pH, and how does a buffer work to resist changes in pH?

• A. pH measures the balance of hydroxide and hydrogen ions but not their actual concentrations.
• B. pH measures hydrogen ion concentration, but buffers only slow changes, not resist them.
• C. pH measures hydrogen ion concentration; buffers raise the pH to a fixed level regardless of added acid or base.
• D. pH measures hydrogen ion concentration; buffers resist changes in pH by neutralizing added acids or bases through weak acid–conjugate base reactions.

Answer: (D)

pH is a measure of how acidic or basic a solution is, based on the concentration of hydrogen ions. It’s a logarithmic scale, so small changes in H+ produce noticeable pH shifts. A buffer works by containing a weak acid and its conjugate base (or a weak base and its conjugate acid). When acid is added, the conjugate base grabs the extra H+ to form the weak acid, so the hydrogen ion concentration doesn’t rise much and the pH stays relatively stable. When base is added, the weak acid donates a proton to neutralize some of the OH−, forming the conjugate base, again limiting pH change. The pH is related to the ratio of the base form to the acid form via the Henderson–Hasselbalch relationship, which explains why buffers hold pH near the pKa. Buffers do have a limit; once you add more acid or base than the pair can handle, the pH will begin to shift more noticeably.

pH is a measure of how acidic or basic a solution is, based on the concentration of hydrogen ions. It’s a logarithmic scale, so small changes in H+ produce noticeable pH shifts. A buffer works by containing a weak acid and its conjugate base (or a weak base and its conjugate acid). When acid is added, the conjugate base grabs the extra H+ to form the weak acid, so the hydrogen ion concentration doesn’t rise much and the pH stays relatively stable. When base is added, the weak acid donates a proton to neutralize some of the OH−, forming the conjugate base, again limiting pH change. The pH is related to the ratio of the base form to the acid form via the Henderson–Hasselbalch relationship, which explains why buffers hold pH near the pKa. Buffers do have a limit; once you add more acid or base than the pair can handle, the pH will begin to shift more noticeably.