Equilibrium Question 390
Question: For preparing a buffer solution of $ pH $ 6 by mixing sodium acetate and acetic acid, the ratio of the concentration of salt and acid should be $ (K_{a}={10^{-5}}) $ [MP PET 1997]
Options:
A) $ 1:10 $
B) $ 10:1 $
C) $ 100:1 $
D) $ 1:100 $
Show Answer
Answer:
Correct Answer: B
Solution:
$ K_{a}={10^{-5}} $ ; $ pH=6 $
$ pH=-\log K_{a}+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $ ; $ 6=-log{10^{-5}}+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $
$ 6=5log10+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $ ; $ 6=5+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $
$ log\frac{[\text{ Salt }]}{[\text{ Acid }]}=6-5=1 $ ; $ \frac{[\text{ Salt }]}{[\text{ Acid }]}=\frac{10}{1} $
