Acids and Bases Equilibria - Buffers

Vocabulary flashcards about buffers, their components, and their calculations, based on lecture notes.

Buffer Solutions

Resist changes in pH when an acid or base is added and act by neutralizing acid or base that is added to the buffered solution.

Acidic Buffer Solution

It must contain significant amounts of both a weak acid and its conjugate base.

Neutralization by Weak Acid

When a strong base is added to an acidic buffer, it is neutralized by the weak acid in the buffer (e.g., HC2H3O2).

Neutralization by Conjugate Base

If a strong acid is added to an acidic buffer, it is neutralized by the conjugate base (e.g., NaC2H3O2) in the buffer.

Henderson-Hasselbalch Equation

An equation derived from the Ka expression that allows us to calculate the pH of a buffer solution.

When to Use Henderson-Hasselbalch Equation

Generally good enough when the 'x is small' approximation is applicable.

'x is small' Approximation Conditions

The initial concentrations of acid and salt are not very dilute, and the Ka is fairly small.

Calculating pH of a Buffer Solution

Steps include writing the balanced equation, preparing an ICE table, and using the Ka expression.

Stoichiometry in Buffer Calculations

The addition of acid or base converts a stoichiometric amount of one buffer component to the other.

Equilibrium in Buffer Calculations

Use ICE table with new initial values after addition of acid or base to calculate [H3O+].

Effect of NaOH on Buffer pH

Adding base to a buffer causes a small increase in pH, while adding base to pure water causes a large increase in pH.

Effect of HCl on HF/NaF Buffer

The addition of a small amount of HCl to a HF/NaF buffer will cause [F-] to decrease and [HF] to increase.

Basic Buffers

Made by mixing a weak base with a soluble salt of its conjugate acid.

Henderson-Hasselbalch for Basic Buffers

Requires looking at the chemical equation as an acid reaction to apply the equation correctly; can also be rewritten in terms of pOH.

Relationship between pKa and pKb

pKa + pKb = 14 (at 25°C)

Buffering Capacity

The amount of acid or base a buffer can neutralize before the pH changes significantly; increases with increasing concentrations of buffer components.

Buffering Range

The pH range within which the buffer can be effective (pKa ± 1).

Effectiveness of Buffers

Depends on the relative amounts of acid and base, and the absolute concentrations of acid and base. A buffer will be most effective when the [base]:[acid] = 1.