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 $



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