Buffers & Buffering Capacity

BUFFERS & BUFFERING CAPACITY
QUESTIONS AND CORRECT ANSWERS

pH_of_a_buffer_solution_depends_on_-
_Correct_answer~_the_pKa_of_the_acid_and_the_ratio_[A-]/[HA].



Henderson-Hasselbalch_equation_-_Correct_answer~_pH_=_pKa_+_log([A-]/[HA])



This_equation_is_used_to_determine_the_pH_of_a_buffer_solution.



Buffer_-
_Correct_answer~_an_aqueous_solution_of_a_WEAK_acid_(HA)_and_its_conjugate_base_(
A-)._They_can_be_made_in_three_ways:

1._Partially_titrating_the_buffer_acid_(HA)_with_a_strong_base.

2._Partially_titrating_the_buffer_base_(A-)_with_a_strong_acid.

3._By_combining_the_weak_buffer_acid_(HA)_and_a_salt_of_the_buffer_acid_in_a_known
_ratio.



Buffer_containing_sufficient_concentrations_of_both_HA_and_A-_-
_Correct_answer~_can_resist_drastic_changes_in_the_pH_upon_addition_of_small_amoun
ts_of_strong_acid_or_strong_base._



This_is_because_buffers_will_react_with_a_strong_acid_to_generate_HA,_or_with_a_stron
g_base_to_generate_A-
._The_buffer_ratio_will_change_depending_on_the_amount_of_strong_acid_or_strong_ba
se_added._The_pH_will_not_change_drastically_until_either_acid_or_base_component_of
_the_buffer_is_consumed.

, Buffer_capacity_-
_Correct_answer~_The_amount_of_strong_acid_or_strong_base_that_can_be_consumed_
by_the_buffer_before_the_pH_changes_dramatically._



-The_capacity_of_the_buffer_to_consume_acid_is_limited_by_the_concentration_of_A-
_present_in_the_original_buffer,_and_the_capacity_of_the_buffer_to_consume_base_in_li
mited_by_the_concentration_of_HA_present_in_the_original_buffer.



monoprotic_acid_-
_Correct_answer~_An_acid_that_can_only_donate_one_proton,_and_is_only_useful_as_a
_buffer_over_a_small_pH_range.



The_purpose_of_a_buffer:_-
_Correct_answer~_to_maintain_a_relatively_constant_pH_in_a_solution



Buffers_are_effective_over_a_range_of_-_Correct_answer~_pH_=_pKa_+/-_1.0



Calculating_buffer_capacity:_-
_Correct_answer~_First,_the_number_of_moles_of_weak_acid_that_are_consumed_by_th
e_strong_base_are_calculated_using_stoich._Then_the_pH_of_the_remaining_buffer_can_
be_calculated_using_the_HH_equation._

*keep_in_mind_that_as_some_of_the_acid_is_being_consumed,_some_of_the_conjugate_
acid_is_being_produced



Common_ion_effect_-
_Correct_answer~_The_shift_in_an_equilibrium_position_caused_by_the_addition_or_pres
ence_of_an_ion_involved_in_the_equilibrium_reaction



Buffered_solution_-
_Correct_answer~_A_solution_that_resists_a_change_in_its_pH_when_either_hydroxide_i
ons_or_protons_are_added