The weak base, e.g. methylamine

CH3NH2(aq) and CH3NH3+(aq) are termed a conjugate base-acid pair. 

If a salt of CH3NH2(aq) is dissolved in water, e.g. CH3NH3Cl(s), it is fully ionised in solution to give CH3NH3+(aq) and Cr(aq). CHsNHs+Caq) is an acid because it donates a proton to the H20(l) which is a base because it accepts the proton. The equation can be labelled 

As in the weak acid case there are several things to notice about these two equilibria  

All three equilibria are examples of proton transfer reactions  

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