[Boxxxed]

pH of 0.065 M base solution is 11.70, what is kb?

14-11.70=2.3

pOH = 0.00501

kb = (acid)(OH-) / (base)

kb = (acid)(0.00501)/ (0.065)

How do I get the acid concentration?

[methic]

Wouldn't it be:

[H₃O] = 10^-11.7

since pH = -log([H₃O)?

[Borek]

How do I get the acid concentration?

Stoichiometry. Write reaction for base dissociation. You know concentration of OH^-, you know initial base concentration - that is enough information to solve for conjugate acid concentration.

[Boxxxed]

How do I get the acid concentration?

Stoichiometry. Write reaction for base dissociation. You know concentration of OH^-, you know initial base concentration - that is enough information to solve for conjugate acid concentration.

Base+H2O--->Acid+H3O

I am still not sure how to solve for acid? This is simpler than all the other problems, don't know why I'm not getting it.

[Boxxxed]

Figured it out. I wasn't subtracting from the initial concentration of base so the answer was always a little bit off.

[Borek]

Base+H2O--->Acid+H3O

You put it on the head.