Speed Bump by Dave Coverly Buffer solution
A solution that contains appreciable amounts of both a
weak acid (HA) and its conjugate base (A ).
In other words we have a solution with appreciable
amount of the acid and its common ion.
It resists pH change when a strong acid or base are
Optimized buffer is when the amount of acid is equal to
the amount of the conjugate base.
Solution (underlined) can react
PS 4 is posted online. You can solve Q 1–7 with an acid A + H O 3 HA + H O 2
with a base HA + OH A + H O 2
See figure 19.3 Demo 6 – Buffer solution – "The Race"
+ the "Rat Race" video clip
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Equal amounts of acid and conjugate base give the
optimum buffer (greatest resistance to pH change).
Typically buffer solutions are effective up to 1 pH unit
either side of the listed buffer pH. 5 6
Solution 1 Buffer and buffer–like solutions
NH violet pH ~ 10.5 First a stoichiometry problem.
Basic solution We need to recalculate concentrations (or moles) based
Solution 2 (a buffer) on a rxn.
NH 4 and NH 3 violet pH ~ 10.5
Then an equilibrium problem.
Create an ICE table with the new concentrations and
calculate the position of equilibrium.
Dry ice (solid CO2) is added to both solutions. It
dissolves and forms carbonic acid.
Add the same amounts of the acid (carbonic acid)
and solution 1 becomes acidic quicker than solution
In our demo solution 1 became yellow (pH ~ 6) while
solution 2 turned light blue (pH ~ 8)
1 L of 0.15 M benzoic acid + 1 L of 0.080 M Sodium Add 1 mL of 1 M HCl (very strong acid), what
benzoate n HA = 0.150 mol nA = 0.080 mol happens ?
First find new concentrations H + lC H 2O H O3+ Cl
0.15 M x 1 L nH3O+ = (HCl)init 0.001 mol
[HA] = = 0.075 M
2L Add 1 ml of 1 M HCl 0.001 mol of HA is formed.
0.080 M x 1 L
[A = = 0.040 M Why ?
+ Rxn of acid and base H 3 + A HA + H O 2
HA + H 2O H 3 + A
I 0.075 0 0.040 M This is the reverse reaction of an acid dissociation
C – x + x + x