A Monoprotic Weak Acid When Dissolved in Water Is 0 $\times$

Multiple Choice

A monoprotic weak acid when dissolved in water is 0.75% dissociated and produces a solution with a pH of 3.11.Calculate the K_a of the acid.

A) 7.6 $\times$ 10^-3
B) 1.0 $\times$ 10^-1
C) 5.9 $\times$ 10^-6
D) Need to know the initial concentration of the acid.
E) None of these.