How are we going to calculate the buffer capacity?

Question

Buffer capacity is the number of moles of strong acid or strong base that 1L of the buffer can absorb without changing pH by more than 1.

Answer 1

Buffer Capacity is the ratio of the increment of strong base or strong acid to the change in pH.


B = êB / êpH



= the small increment in gram equivalents/liter of strong base (or acid) added to buffer solution to produce a pH change of êpH.


B = (2.3 x C x Ka [H+] ) / (Ka + [H+])2

B = 2.3 C a (1 - a)

C = [Acid] + [Salt]
or
C = [Base] + [Salt]

Example:

Calculate the buffer capacity (B) for a mixture of 0.01 moles of acetic acid and 0.03 moles of NaOAc in 100 mL of total solution. pKa = 5.24



pH = pKa + log (salt/acid) = 4.76 + log 0.03/0.01 = 5.24

[H+] = 5.75 x 10-6

C = (0.01 + 0.03) moles/100 mL = 0.4 M

pKa = 4.76

Ka = 1.74 x 10-5

B = (2.3 x C x Ka [H+] ) / (Ka + [H+])2

B = ( 2.3 x 0.4 x 1.74 x 10-5 x 5.75 x 10-6 ) / (1.74 x 10-5 + 5.75 x 10-6)2

B = ( 9.20 x 10-11 ) / ( 5.36 x 10-10 ) = 0.172

Using other equation:

B = 2.3 C a (1- a )

C = (0.01 + 0.03) moles/100 mL = 0.4 M

a = (0.03)/(0.03 + 0.01) = 0.75

B = 2.3 x 0.4 x 0.75 x (1 - 0.75)
B = 2.3 x 0.4 x 0.75 x 0.25 = 0.172

Answer 2

Calculating Buffer Capacity

Answer 3

Buffer Capacity Equation

Answer 4

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RE:
How are we going to calculate the buffer capacity?
Buffer capacity is the number of moles of strong acid or strong base that 1L of the buffer can absorb without changing pH by more than 1.

Answer 5

The example shown here uses inaccurate number for pKa.