Buffers

Question 1

Buffer definition

Answer 1

a solution that resists change in pH when small amounts of acid/alkali are added

-acidic buffers = pH < 7
- basic buffers = pH < 7

Question 2

What are buffers used in?

Answer 2

Shampoos and biological washing powders

Question 3

explain qualitatively the action of acidic buffers.

Answer 3

HA –> [H+] + [A-]
HA = acid
A- = salt

adding [H+]:
H+ conc increases
H+ combines with A- so the equilibrium will move to the LEFT in order to make HA, so pH doesnt change much.
ratio of [HA]:[A-] remains constant - IMPORTANT MARKING POINT

adding [OH-]:
OH- increases
OH- combines with H+ so H+ decreases, so equilibrium will shift to the RIGHT in order to replace the lost H+.
[H+] increase close to its original value, so pH doesnt change much.
ratio of [HA]:[A-] remains constant - IMPORTANT MARKING POINT

Question 4

explain qualitatively the action of basic buffers.

Answer 4

B + H2O –> BH+ + OH-
B = base
BH+ = ion salt of the base

adding [H+]:
H+ increases, it combines with OH- so OH- decreases. Equilibrium shifts to the RIGHT to replace the lost OH-
Now, OH- conc increases close to its original value so pH doesnt change much.

adding [OH-]:
OH- increases, it combines with the BH+ so equilibrium will shift to the LEFT. OH- decreases and goes back to its original value, so pH doesnt change much.