how do you identify the base in this reaction?

h2o(L) + CH3NH2(aq) yields OH-(aq) + CH3+(aq)

I think that the base always contains hydroxide, aka OH; the original components were water mixed with an ammonium compound ( NH2)Check the chemistry reference tables too, which have tables that identify the bases and acids.

You have a typo, actually an omitted portion, in your post. You should have posted

H2O(l) + CH3NH2 ==> OH^- + CH3NH3^+
How do you know which is the base? If you go by the Arrhenius theory the base produces OH^- in solution. In this case it is easier, I think, to use the Bronsted-Lowry theory. The base is the one that takes a proton away from something. In this case, CH3NH2 took a proton away from H2O to form the CH3NH3^+.

To identify the base in this reaction, you need to understand that the base is the species that accepts a proton (H+). In this case, the species that gains an additional H+ is the base. Let's analyze the reaction:

H2O(L) + CH3NH2(aq) yields OH-(aq) + CH3+(aq)

In the reaction, water (H2O) loses a proton (H+) to form a hydroxide ion (OH-). Therefore, water acts as an acid.

On the other hand, CH3NH2 gains a proton to form CH3+. Hence, CH3NH2 is the base because it accepts a proton (H+) to form CH3+.

So, in this reaction, CH3NH2 is the base.

To identify the base in this reaction, you need to understand the concept of acid-base reactions and use the Bronsted-Lowry theory.

According to the Bronsted-Lowry theory, an acid is a substance that donates a proton (H+), while a base is a substance that accepts a proton. In this reaction, the base will be the species that is accepting a proton.

Let's analyze the reaction:
H2O(L) + CH3NH2(aq) yields OH-(aq) + CH3+(aq)

In this equation, water (H2O) acts as a base because it accepts a proton from the methylamine (CH3NH2), which acts as an acid. Water gains a proton and forms hydroxide ions (OH-).

Therefore, in this reaction, the base is water (H2O).