Calculate molar concentrations 10 points best answer?

Question

calculate molar concentrations of H+ and OH- in solutions that have the following pH values

a. 3.14

b. 2.78

c. 9.25

d. 13.24

Please include how to do it as well

Answer 1

pH = -log[H+]... each of these will give the concentration of H+ if you just use for example: 10^-3.14

The OH- concentration is just for example: 14-3.14 = 10.86 = pOH and pOH = -log[OH-] and then you do 10^-10.86 which equals [OH-]

Answer 2

pH=log(pKa)

pKa= 10^pH

pKa=[OH-]/[H+]

Just do the math!  

Sorry - edit:

Or you can use the equation pKa = pH - log([base]/[acid])