What best describes a buffer solution?

What best describes a buffer solution?

• A. A solution that cannot neutralize added acids or bases.
• B. A solution containing a strong acid and a strong base in equal amounts.
• C. A solution containing a weak acid and its conjugate base.
• D. A solution with a high concentration of H3O+.

Answer: (C)

Buffers resist changes in pH because they contain a weak acid and its conjugate base (or a weak base and its conjugate acid). When a small amount of acid is added, the conjugate base neutralizes the extra H+, helping keep the pH stable. When a small amount of base is added, the weak acid donates protons to neutralize it, again helping to stabilize the pH. This balance is often described by pH ≈ pKa + log([A-]/[HA]), meaning the pH stays near the acid’s pKa as long as both species are present. A common example is a solution containing a weak acid and its conjugate base, like acetic acid and acetate, which buffers around the pH near 4.8. In contrast, a solution that cannot neutralize added acids or bases won’t resist pH changes; a strong acid and strong base in equal amounts simply neutralize to water and salt and don’t provide ongoing buffering; and a solution with a high concentration of H3O+ is strongly acidic and lacks buffering behavior.

Buffers resist changes in pH because they contain a weak acid and its conjugate base (or a weak base and its conjugate acid). When a small amount of acid is added, the conjugate base neutralizes the extra H+, helping keep the pH stable. When a small amount of base is added, the weak acid donates protons to neutralize it, again helping to stabilize the pH. This balance is often described by pH ≈ pKa + log([A-]/[HA]), meaning the pH stays near the acid’s pKa as long as both species are present. A common example is a solution containing a weak acid and its conjugate base, like acetic acid and acetate, which buffers around the pH near 4.8. In contrast, a solution that cannot neutralize added acids or bases won’t resist pH changes; a strong acid and strong base in equal amounts simply neutralize to water and salt and don’t provide ongoing buffering; and a solution with a high concentration of H3O+ is strongly acidic and lacks buffering behavior.