Equilibrium Question 415
Question: The $ pK_{a} $ of a weak acid is 4.8. What should be the ratio of [Acid]/[Salt] of a buffer if $ pH=5.8 $ is required [MP PET 2003]
Options:
A) 10
B) 0.1
C) 1
D) 2
Show Answer
Answer:
Correct Answer: B
Solution:
$ pH=pK_{a}+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $
$ 5.8=4.8+\log \frac{[\text{ Salt }]}{[\text{ Acid }]} $ or $ log\frac{[\text{ Salt }]}{[\text{ Acid }]}=1.0 $
$ \frac{[\text{ Salt }]}{[\text{ Acid }]}=antilog1.0=10 $ \ $ \frac{[\text{ Acid }]}{[\text{ Salt }]}=\frac{1}{10}=0.1 $
