Exam 2 Pt. 3 - Buffers

What conditions must be met for a solution be considered a buffer?

1. Weak acid and its conjugate base

2. Weak base and its conjugate acid (NH3)

MUST BE A PAIR

When an acid is added to a buffer solution, what neutralizes it? Why do you need to know this?

• Conjugate base neutralizes it

for calculating pH CHANGES

When a base is added to a buffer solution, what neutralizes it? Why do you need to know this?

• Weak acid neutralizes it

for calculating pH changes

What are the two ways two find pH of a buffer?

1. ICE table

2. Henderson Hasselbach Equation (use this one)

What does pKa mean?

• pKa = -log(Ka)

What are the HH equations (given, just know how to use)?

• pH = pKa + log ([CB]/[acid])

• pH = pKa + log (mol CB/mol acid)

What does adding acid to a buffer solution do to its pH?

• Decreases buffer’s pH

What does adding base to a buffer solution do to its pH?

• Increases buffer’s pH

What are 2 steps to calculating pH changes in a buffer solution (once adding base/acid to solution)?

1. Stoichiometric calculation; neutralization reaction (BCA table)

2. Equilibrium calculation 

What must first be done to concentrations of acid and bases given before using BCA table?

• Convert all concentrations to mols

When writing the neutralization reaction for the BCA table, what two reactants do you choose?

• Adding acid; CB neutralizes it

• Adding base; weak acid neutralizes it

In the BCA table, what mols do you subtract/add in the “C” area?

• Subtract/add smallest/limiting reactant

Once mols after neutralization are determined, what do you do in the equilibrium calculation?

• Use HH equation or ICE table

When can you only use the HH in the equilibrium concentration?

• Can only use HH equation; when identifying buffer (weak acid + CB)

When are buffers most effective (pH resistant) in relation to [base] and [acid]? What two values should it be between?

• Buffer most effective; [base] approx. = [acid]

between 0.1 and 10

When are buffers more effective in relation to amount of concentrations of acid and base?

• Buffers more effective; with higher concentrations of acid and base

What is the effective pH range of a buffer system?

• + or - 1 from pKa

What is buffer capacity?

• Amount of acid or base that can be added without destroying buffer

How do you know when an acid or base will destroy buffer?

• Acid destroys buffer; uses up all of CB

• Base destroys buffer; uses up all of weak acid