Chemistry

This problem tests whether you recognize that an extremely weak acid (tiny $K_a$) barely dissociates, so the $\text{H}^+$ ions come almost entirely from water's autoionization, not the acid itself. Set up the equilibrium expression for the acid, but notice that $K_a$ is so small that you can assume nearly all the acid remains undissociated—this lets you solve without the quadratic formula. The key insight is that in such a dilute, weakly acidic solution, water's contribution to $\text{H}^+$ becomes significant and must be accounted for carefully.

This problem tests whether you recognize that an extremely weak acid (tiny $K_a$) barely dissociates, so the $\text{H}^+$ ions come almost entirely from water's autoionization, not the acid itself. Set up the equilibrium expression for the acid, but notice that $K_a$ is so small that you can assume nearly all the acid remains undissociated—this lets you solve without the quadratic formula. The key insight is that in such a dilute, weakly acidic solution, water's contribution to $\text{H}^+$ becomes significant and must be accounted for carefully.