Equilibrium Question 458
Question: How much sodium acetate should be added to a $ 0.1m $ solution of $ CH_3COOH $ to give a solution of $ pH=5.5,(pK_{a} $ of $ CH_3COOH=4.5) $ [KCET 1996]
Options:
A) $ 0.1m $
B) $ 0.2m $
C) $ 1.0m $
D) $ 10.0m $
Show Answer
Answer:
Correct Answer: C
Solution:
$ pH=pK_{a}+log\frac{[\text{ Salt }]}{[\text{ Acid }]} $ ; $ 5.5=4.5+log\frac{[\text{ Salt }]}{[\text{ 0}\text{.1 }]} $
$ log\frac{[\text{ Salt }]}{0.1}=5.5-4.5=1 $
$ \frac{[\text{ Salt}]}{0.1}= $ antilog 1 = 10 ; $ [\text{ Salt }]=1 $
