concentration of H3O and OH-

[melissa_dis4K]

How do I answer the following question. All I know is that Kw=[H3O+][OH-]
Estimate the concentrations of (a) [H3O+] and (b) [OH-] at 25 C in
6.0 x 10^-5 m HI(aq).
[Answer: (a) 60. mumol/L; (b) 0.17 nmol/L]
Thank you

[Sarah Kiamanesh 1D]

Basically, because hydroiodic acid is a strong acid, it dissociates completely in an aqueous solution. This means that the hydronium concentration is equivalent to the initial molarity of the acid. The back of the book represented this value in micromoles, so instead of just writing it as 6.0x10^-5, they wrote it as 60 micromoles. To get the hydroxide ion concentration, we just divide the autoprotolysis constant (10^-14) by the hydronium ion concentration to get 1.7x10^-10.