Chapter 8: monoprotic acid-base equilibrium

pX

negative logarithm of X

Conjugate acid-base pair

they are related by the gain or loss of a proton (H+)

Acid: HA

Conjugate base: A-

Base: B

Conjugate acid: BH+

HA is a weak acid, so it is normally much stronger than water

TRUE

Hence, [A-] » [OH-] and [H+] = [A-]

Buffer

A solution that resists pH change upon the addition or dilution of small amounts of acids or bases

Formed by the mixing of an acid and its conjugate base (or vice versa)

• If a weak acid is mixed with its conjugate base, the amounts of acid and base change little

For every 10x change in [A-]/[HA], the pH changes by 2 unit

FALSE

*It changes by ONE unit

As the base concentration in [A-] increases…

pH goes UP

As the acid concentration [HA] increases…

pH goes DOWN

pH of a buffer is nearly independent of its volume

TRUE (dilution doesn’t significantly change it)

A buffer resists pH changes because the added strong acid or base are consumed by…

[A-] or [HA]

Buffer capacity

the amount of acid or base a buffer can neutralize before pH changes significantly (the number of moles per liter needed to produce)

Maximum buffer capacity occurs when pH = pKa (equal amounts of acid and base)