Determine the hydronium ion concentration

in a solution that is 0.00027 M HCl.
Answer in units of M.

Determine the hydroxide ion concentration in
a solution that is 0.00027 M HCl.
Answer in units of M.

This is a two part question and I have tried multiple times and every time I try a new answer it's wrong. Can someone help me please! Thanks in advance!

1 answer

If you had posted your work I wouldn't have to guess what you did.
M HCl = 2.7E-4
pH = -log(HCl) since HCl is a strong acid and ionizes 100%.

Then (H^+)(OH^-) = Kw = 1E-14