Equilibrium Question 833

Question: A buffer solution is prepared by mixing 10 mL of $ 1.0M,CH_3COOH $ and 20 mL of 0.5 M $ CH_3COONa $ and then diluted to 100 mL with distilled water. If $ pK_{a} $ of $ CH_3COOH $ is 4.76, what is the pH of the buffer solution'

Options:

A) 5.8

B) 4.34

C) 5.21

D) 4.76

Show Answer

Answer:

Correct Answer: D

Solution:

Total volume $ =100mL $

$ [ acid ]=10mL\times \frac{1.0}{100}=0.1 $

$ [ salt ]=20mL\times \frac{0.5}{100}=0.1 $ pH of acidic buffer $ =pK_{a}+\log \frac{[salt]}{[acid]} $

$ =4.76+log\frac{0.1}{0.1}=4.76 $



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