Question

In one experiment, 50.0ml of 0.10M CH3NH2, is mixed with 20.00ml of 0.10 M CH3NH3Cl. The kb of CH3NH2 is 3.70*10^-4.

a) write the chemical reaction for the equilibrium which becomes established, using H2O as a reactant.
b)Write the net-ionic equation that occurs when Ba(OH)2 is added to the mixture.

For A, would the equilibrium equation be H2O(l)+CH3NH2(aq)-->H30+(aq) + CH3NH-(aq)?

Please clarify and help with B.

Answer 1

What happens when we add NH3 to H2O?
NH3 + HOH ==< NH4^+ + OH^- and I'm sure you have seen this reaction many times. So if we replace one of the H atoms on NH3 with a methyl group (CH3), wouldn't the reaction be analogous?
CH3NH2 + HOH ==> CH3NH3^+ + OH^-

For part b, you can look at it two ways. One way is that adding Ba(OH)2 adds the common ion, OH^-, and by Le Chatelier's principle, that shifts the equilibrium to the left producing H2O and CH3NH3. The second way is to look at it as an acid/base reaction.
CH3NH3^+(acid) + Ba(OH)2(base) ==>

CH3NH3^+ + OH^- ==> CH3NH2 + HOH.
I suspect that Ba(OH)2 is a strong enough base that CH3NH2 could be broken up and NH3 might be evolved.