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} $



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