Chemistry;
posted by Sharon .
for a solution of the weak base, 0.075 M ethylamine C2H5NH2(aq), the hydroxide ion concentration (OH) is 6.6x10^3 M. Assume that temperature is constant and volumes are additive.
a. Write the equilibrium dissociation equation.
b. What's the pH of 0.075 M C2H5NH2(aq)?
c. What's the value of Kb?
Please show your work on how you calculate it so I can see how you figured it out. Thanks.

C2H5NH2 + HOH ==> C2H5NH3^+ + OH^
You know OH^; therefore,
pOH = log(OH^) and
pH + POH = pK2w = 14. Solve for pH.
Write the Kb expression
Substitute OH^ = 0.0066
(C2H5NH3^+) = 0.0066
(C2H5NH2) = 0.0750.0066
Solve for Kb. 
Thanks! This was very helpful.

pH + pOH = pKw = 14 (and not pK2w)
(Kw has no K2).