In a 0.2 ~M aqueous solution, lactic acid is 6.9 % dissociated. The value of dissociation constant is

Step-by-step solution

For a weak acid dissociation HA H⁺ + A⁻ , the dissociation constant K_a is given by the expression K_a = c ^2 1 - . Given concentration c = 0.2 M and degree of dissociation = 6.9 % = 0.069 . Since is small, we can approximate 1 - 1 , so K_a c ^2 . Substituting the values: K_a = 0.2 (0.069)^2 . K_a = 0.2 0.004761 = 0.0009522 . Expressing in scientific notation, K_a = 9.522 10⁻⁴ 9.5 10⁻⁴ . Answer: 9.5 10⁻⁴