Buffer solutions

What is a buffer solution?

a system that minimises pH changes on addition of small amounts of an acid or base

How do you prepare a buffer solution? (The 2 ways)

a weak acid and a salt of the weak acid

Excess of a weak acid and a strong alkali

What is an example of forming a buffer solution from a weak acid and salt of the weak acid?

CH₃COOH and CH₃COONa

How is a buffer solution prepared by partial neutralisation of the weak acid?

adding an aqueous alkali solution such as NaOH to an excess of the weak acid (CH₃COOH)

What is the conjugate acid-base pair? What is an example?

HA_(aq)/A^-_(aq)

E.g CH₃COOH / CH₃COO-

When preparing a buffer solution from a weak acid and its salt, what is the source of the conjugate base component?

the salt: when the salt is added to water, the salt completely dissolves so is the source of the conjugate base component

What happens when an acid is added to the buffer solution_

[H+] increases

H+ ions react with the conjugate base, A-

Equilibrium shifts to the left to remove H+ ions

What happens when an alkali is added to the buffer solution?

[OH-] increases

The concentration of H+ ions react with the OH- ions to form H2O

HA dissociates to restore H+ ions

A buffer is most effective when what?

there are equal concentrations of the weak acid and its conjugate base

When [HA] = [A-], what is true?

pKa = pH

Ka = [H+]

How do you calculate the pH of a buffer solution?

Using Ka

The pH of the blood needs to be maintained between which values?

7.35 - 7.45

The carbonic acid-hydrogencarbonate buffer system operates how when an acid is added?

[H+] increases

H+ ions react with the conjugate base, HCO₃-

Equilibrium shifts to the left

What happens when an alkali is added to the carbonic acid-hydrogencarbonate buffer system?

[OH-] increases

H+ ions react with OH- ions to form H2O

H₂CO₃ dissociates so equilibrium shifts to the right

Why does excess of a weak acid and a strong base create a buffer solution?

partial neutralisation of the weak acid

contains both the weak acid and the conjugate base