MCQ
The condition for minimum change in $pH$ for a buffer solution is
- AIsoelectronic species are added
- BConjugate acid or base is added
- ✓$pH = p{K_a}$
- DNone of these
✓
Answer
Correct option: C.
$pH = p{K_a}$
c
Buffers work best when $pH = pK _{ a }$
Buffers work best when $pH = pK _{ a }$
From the Henderson-Hasselbalch equation
$pH = pK _{ a }+\log 10 \frac{[ A -]}{[ HA ]}$
If $\operatorname{pH}= pK _{ a } \Longrightarrow \log 10 \frac{[ A -]}{[ HA ]}=0 \Longrightarrow \frac{[ A -]}{[ HA ]}=1$
buffer exhibits the highest resistance to acid and base addition for the equimolar solution (when $pH = pKa$ ). From the plot, it is also obvious that buffer capacity has reasonably high values only for $pH$ close to $pKa$ value. The further from the optimal value, the lower buffer capacity of the solution
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