Answer : The value of [tex]k_a[/tex] for benzoic acid is, [tex]6.4\times 10^{-5}[/tex]
Solution :
The balanced equilibrium reaction will be,
[tex]C_6H_5COOH\rightleftharpoons H^++C_6H_5COO^-[/tex]
initial conc. 0.2 M 0 0
at eqm. [tex](0.2-0.00355)M[/tex] [tex]0.00355M[/tex] [tex]0.00355M[/tex]
The expression for dissociation constant for a benzoic acid will be,
[tex]k_a=\frac{[H^+]\times [C_6H_5COO^-]}{[C_6H_5COOH]}[/tex]
Now put all the given values in this formula, we get the value of [tex]k_a[/tex]
[tex]k_a=\frac{(3.55\times 10^{-3})\times (3.55\times 10^{-3})}{(0.2-3.55\times 10^{-3})}=6.4\times 10^{-5}[/tex]
Therefore, the value of [tex]k_a[/tex] for benzoic acid is, [tex]6.4\times 10^{-5}[/tex]
