What is pH when HCl(aq) is added to an aqueous solution of "methylamine"?

1 Answer
anor277
Apr 28, 2017

See this old answer [here.](https://socratic.org/questions/how-do-buffers-maintain-ph)

Explanation:

The defining relationship is.............

Thus pH=pK_a+log_10{[[A^-]]/[[HA]]}

And here the following equilibrium is interrogated,

H_3CNH_2 + H_2O rightleftharpoons H_3CNH_3^(+) + HO^-

So for the purposes of your question, A^(-)-=H_3CNH_2, and HA-=H_3CNH_3^+.

You originally had H_3CNH_2, at EQUIVALENCE you have H_3CNH_3^+. You have NOT supplied pK_a for H_3CNH_3^+, and you are going to need this. Remember that as you add titrant, the volume of the solution is going to change, as is the molar concentrations of the reagents.

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