buffers Flashcards
define buffer
a system which minimises pH change on addition of small amounts of an acid or base
state the 2 ways that an acidic buffer is formed
- weak acid & salt of weak acid
- excess weak acid & alkali
give an example of a weak acid and salt forming a buffer
CH3COOH + CH3COO-Na+
give an example of a weak acid and strong alkali forming a buffer
CH3COOH + NaOH
how do buffers work when a small amount of acid is added?
- equilibrium shifts left
- the excess added H+ ions react with A- from the conjugate base so more HA is produced
how do buffers work when a small amount of alkali is added?
- equilibrium shifts right
- alkali increases the OH- ions present which react with the H+ and lower [H+]
- therefore equilibrium shifts to the products to replace the lost H+ ions
give the equation for adding acid
HA = H+ + A-
- when acid is added the [H+] increases
- so equilibrium shifts left to minimise this
give the equation for adding alkali
H+ + OH- = H2O
- when alkali is added the [OH-] increases and reacts with H+ forming more H2O
- so equilibrium shifts right to replace the lost H+
what is the calculation for [H+] ?
10^-pH
what is the calculation for pH?
-log [H+]
what is the calculation for Ka?
[H+] [A-] / [HA]
what is the calculation for [H+] when using Ka?
[H+] = Ka x ([HA]/[A-])
what is the range of blood pH?
7.35-7.45
what is the equation for maintaining blood pH?
H2CO3 = HCO3- + H+
what happens when [H+] in blood increases?
H+ and CO3- combined
- equilibrium shifts left
