[duma]

Write the Henderson-Hasselbalch equation for a solution of methylamine. Calculate the quotient [CH3NH2]/ [CH3NH􏰀3 ] at (a) pH 4.00; (b) pH 10.645; (c) pH 12.00.


So this is what I got....But I don't know why it is correct.

ph = 4.0 + log( [CH3NH2]/ [CH3NH􏰀3 ])

10^ (ph - 4.0) =  [CH3NH2]/ [CH3NH􏰀3 ]

 [CH3NH2]/ [CH3NH􏰀3 ] = 2.26x10^-7

Can you explain why it tells us to plug the given pH into where the pKa is supposed to be?



Thanks

[Borek]

Doesn't look correct to me. It is not even clear for which pH of the three listed you did calculations.

First things first, what is pKa for methylamine?