Equilibrium Question 508
Question: The ionization constant of a certain weak acid is $ {10^{-4}} $ . What should be the [salt] to [acid] ratio if we have to prepare a buffer with pH = 5 using this acid and one of the salts [CPMT 2000; KCET 2000; Pb. CET 2000]
Options:
A) $ 1:10 $
B) $ 10:1 $
C) $ 5:4 $
D) $ 4:5 $
Show Answer
Answer:
Correct Answer: B
Solution:
$ pH=-\log K_{b}+\log \frac{[salt]}{[\text{ acid }]} $
$ 5=-\log {10^{-4}}+\log \frac{[salt]}{[\text{ acid }]} $
$ \log \frac{[salt]}{[\text{ acid }]}=1 $
$ \frac{[salt]}{[\text{ acid }]}=antilog,1=10:1 $
