For the strong acids find the [H3O]and [OH] in a solution that is .785% HNO3 by mass (assume a density of 1.01 g/ml). If someone could offer step by step instructions, that would be terrific!

Answer 1

0.785% w/w means 0.785 g HNO3/100 g soln.
Density = 1.01 g/mL; therefore, the 100 g soln has a volume of 99 mL.
0.785 g is how many mols? That's 0.785/63 = approximately 0.012 and the M = mols/L = 0.012 mols/0.099 L = approximately 0.13M. (You need to redo all of this and use better numbers).
(H3O^+) = 0.13M
(H3O^+)(OH^-) = Kw = 1E-14
You know H3O^+ and Kw, solve for OH^-

Answer 2

Thank you so much for your help! I was able to follow your steps very well! Much appreciated DrBob222!