Question

The dissociation constant of acetic acid is $x \times 10^{-5}$ When $25 \,mL$ of $0.2 \,M \,CH _3 COONa$ solution is mixed with $25 \,mL$ of $0.02\, M \,CH _3 COOH$ solution, the $pH$ of the resultant solution is found to be equal to 5. The value of $x$ is ___

Answer 1

The correct answer is 10
Buffer of HOAc and NaOAc
pH=pKa+log0.010.1​
5=pKa+1
pKa=4
Ka=10−4
x=10