
To decide:
Which buffer experiences a smaller change in the
a) The same small quantity of strong base is added to both
b) The same small quantity of strong acid is added to both

Answer to Problem 16.20QA
Solution:
a) When the same small quantity of strong base
b) When the same small quantity of strong acid
Explanation of Solution
Let’s consider acetic acid and sodium acetate buffer systems with different concentrations of conjugate acid base pairs. Let’s assume the volume for two buffers is equal as
In buffer A, concentrations of conjugate acid base pair are nearly equal.
Let’s assume the moles of conjugate acid and base to be
In buffer A,
Total concentration of conjugate acid base pair is
So, for buffer A, the initial pH will be equal to
In buffer B, total composition of conjugate acid base pair remains the same, but there is twice as much as weak acid as its conjugate base.
Let’s assume the moles of conjugate acid and base to be
In buffer B,
Solving the above equations, we get the concentrations of
For buffer B, the initial
Part a)
Consider that 0.01 moles of
For buffer A:
RICE table for reaction:
Reaction | |||
Initial | |||
Change | |||
Final |
The mole ratio of
Change in pH in buffer A
For buffer B:
RICE table for reaction:
Reaction | |||
Initial | |||
Change | |||
Final |
The mole ratio of
Change in pH in buffer B
When the same small quantity of strong base
Part b)
Consider that 0.01 moles of
Buffer A:
RICE table for reaction:
Reaction | |||
Initial | |||
Change | |||
Final |
The mole ratio of
Change in pH in buffer A
For buffer B:
RICE table for reaction:
Reaction | |||
Initial | |||
Change | |||
Final |
The mole ratio of
Change in pH in buffer A
When the same small quantity of strong acid
Conclusion:
For buffers, the greater the concentrations of the conjugate pair components, the greater is its buffer capacity, that is, the greater is its ability to withstand additions of acid or base without a significant change in
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Chapter 16 Solutions
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