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1.
The concept of buffer solution
Many chemical reactions carried out in aqueous solutions need to be within a certain pH range to proceed smoothly
.
For example, in the formation reaction of [Fe(C 2 O 4 ) 3 ] 3- , if the pH is too low, C 2 O 4 2- is easy to combine with H + to reduce its coordination ability, which is not conducive to the formation of complex ions, and the pH is too high Then Fe 3+ produces Fe(OH) 3 with low solubility, which is not conducive to the formation of complex ions
Add a small amount of strong acid, strong base or dilute with a large amount of water to keep the pH of the system unchanged is called a buffer solution
.
[Example 7-5] Calculate [H + ] and pH in the mixed solution of 0.
1 mol·dm -3 HAc and 0.
1 mol·dm -3 NaAc .
When 0.
01 mol HCl and 0.
01 mol NaOH are added to this mixed solution of 1dm 3 , what is the pH value?
However, when 0.
01 mol HCl was added to 1 dm 3 pure water, the pH of the system changed from 7 to 2, which was significantly reduced; after 0.
01 mol NaOH was added to pure water, the pH of the system changed from 7 to 12, which was significantly increased
The reason why the buffer solution has a buffering effect, keeping the pH of the system basically unchanged, is essentially the same ion effect
.
There is a dissociation equilibrium of HAc in HAc-NaAc solution
Equilibrium constant
The change of system pH mainly depends on the concentration ratio of [HAc] and [Ac] in the system
.
Since small values of HAc KaΘ, [HAc] and [Ac - ] concentration is approximately equal to the initial concentration of HAc and NaAc solution
Related Links: Same Ion Effect and Salt Effect