another buffer problem?

Question

How many moles of HCL must be added to 100 mL of a 0.100 M solution of methylamine (pK(b) = 3.36) to give a buffer having a pH of 10.0?

numbers and letters in ( ) are subscripts
please show work
thanks

Answer 1

pOH = pKb + log[Salt]/[Base]

or 4 = 3.36 + log (x/(.01-x)) {x is the moles of HCl added}

or x/(.01-x) = .64

or 100x/(1-100x) = .64

or 100x = .64 - 64x

or x = .64/164 = 3.9x10^-3 mol.