Question

question 11 (1 point)
a buffered solution ________.
○ fails to keep hydronium and hydroxide ion concentrations nearly constant when strong acids or bases are added.
○ acts to keep the hydroxide ion concentration nearly constant.
○ acts to keep the hydronium ion concentration nearly constant.
○ maintains a constant or nearly constant ph when small amounts of strong acids or bases are added.

Explanation:

A buffered solution resists changes in pH. It contains a weak acid - conjugate base or weak base - conjugate acid pair. When small amounts of strong acid (adds \(H_3O^+\)) or strong base (adds \(OH^-\)) are added, the buffer components react to neutralize them. For example, if a strong acid is added to a buffer of \(HA\) (weak acid) and \(A^-\) (conjugate base): \(A^-+H_3O^+\to HA + H_2O\). If a strong base is added: \(HA+OH^-\to A^-+H_2O\). Since \(pH =-\log[H_3O^+]\), and the buffer keeps \([H_3O^+]\) relatively constant (by neutralizing added \(H_3O^+\) or \(OH^-\) which would otherwise change \([H_3O^+]\)), the pH remains nearly constant. The first option is wrong as buffers do keep \([H_3O^+]\) (and related \([OH^-]\) via \(K_w=[H_3O^+][OH^-]\)) nearly constant. The second and third options are too narrow as buffers maintain a balance for both \(H_3O^+\) and \(OH^-\) (through the buffer reactions) to keep pH (which depends on \(H_3O^+\) concentration) nearly constant, not just one ion.

Answer:

maintains a constant or nearly constant pH when small amounts of strong acids or bases are added.