|Buffers are solutions with the ability to resist the
strong acids or strong bases, within limits.
|They play an important role in chemical processes where it
that a fairly constant pH is maintained. In many industrial and
processes, specific reactions occur at some optimum pH value. When the
pH varies to any extent from the optimum value, undesirable reactions
effects may occur. For example, the pH of your blood lies at about
If this value drops below 7.0 (acidosis) the results are fatal. Also if
it rises above 7.7 (alkalosis) the results are as well fatal.
our blood contains a buffering system which maintains the acidity at
proper level. If it were not for the protection of the buffering
we could not eat and adsorb many of the acidic fruit juices and foods
|A typical lab buffer is CH3COOH and its salt
Most buffer solutions are made up using a weak acid and its sodium
When a strong base such as NaOH is added to the buffer, the acetic acid
reacts with and consumes the excess OH- ion. The OH-
reacts with the H3O+ ion from the acid in the
H2O + CH3COOH
H3O+ + CH3COO-
+ OH- <----------> H2O
|The OH- reduces the H3O+
which causes a shift to the right, forming additional CH3COO-
and H3O+ ions. For practical purposes each mole
OH- added consumes a mole of CH3COOH and produces
a mole of CH3COO-.
+ CH3COOH <------------> CH3COO-
|When a strong acid such as HCl is added to the buffer, the
ions react with the CH3COO- ions of the salt and
form more undissociated CH3COOH.
+ CH3COO- <----------->
CH3COOH + H2O
|As you would expect, there is a limit to the quantity of H+
or OH- that a buffer can absorb without undergoing a
change in pH. If a mole of HCl is added to a litre of buffer solution
0.5 moles of sodium acetate/acetic acid buffer the H+
consumes the buffer and results in a drastic change in pH.
|The blood buffer is made up from the dissolved carbon
CO2(g) + H2O <-------> H2CO3
<------> HCO3- + H3O+
|When a base is added it reacts with the carbonic acid.
OH- + H2CO3 <--------> HCO3-
|When an acid is added it reacts with the bicarbonate ion.
H3O+ + HCO3-
<---------> H2CO3 + H2O
|Because there are both a base-neutralizer and an
then we have a buffer.
|A buffer has two components.
NaA ---> Na+ + A-
a weak acid & a soluble salt of the acid
|Therefore any extra H3O+ will be
by the A- in the buffer.
H3O+ + A-
HA + H2O
|And any extra OH- that is added will be
HA + OH- <------> A- + H2O
|There are 3 basic types of calculations that can be done with buffer system and these will be covered next.|