JEE Main On 8 April 2017 Question 29
Question: Addition of sodium hydroxide solution to a weak acid (HA) results in a buffer of pH 6. If ionization constant of HA is 10-5, the ratio of salt to acid concentration in the buffer solution will be : [JEE Online 08-04-2017]
Options:
A) 10 : 1
B) 4 : 5
C) 5 : 4
D) 1 : 10
Show Answer
Answer:
Correct Answer: A
Solution:
$Ka=10^{−5}$
$pKa=−logKa=−log10^{−5}=5$
$pH=pKa+log\frac{[salt]}{[acid]}$
$6=5+log\frac{[salt]}{[acid]}$
$1=log\frac{[salt]}{[acid]}$
$\frac{[salt]}{[acid]}=\frac{10}{1}$
