Why do methylamine and ethylamine have nearly the same basicity constant?

It is known that **ethyl** has a *stronger* inductive effect than **methyl**.
Its positive inductive effect is greater than methyl.


Then why does ethylamine has a $\mathrm{p}K\_\mathrm{b}$ of $3.35$ and methylamine has the $\mathrm{p}K\_\mathrm{b}$ of $3.34$
($\mathrm{p}K\_\mathrm{b}$ values in water)
Shouldn't the $\mathrm{p}K\_\mathrm{b}$ of ethylamine be **lower** than methylamine?




Ethylamine has a pKb slightly greater than that of methylamine.


As you are saying



> 
> It is known that ethyl is better than methyl for inductive effect. It's positive inductive effect is greater than methyl.
> 
> 
> 


is absolutely true. But the basicity in aqueous medium is not only determined by +I effect but also solvation of substituted ammonium cation.


Even though +I effect in ethylamine is more than that in methylamine, ethylamine is more bulkier and sterically hinders the formation of intermolecular H−bonds with water.


[![enter image description here](https://i.stack.imgur.com/vjSNl.gif)](https://i.stack.imgur.com/vjSNl.gif)


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The difference of methyl’s and ethyl’s inductive effects is very small.


Likewise, the difference in $\mathrm{p}K\_\mathrm{b}$ values is very small.


Both are in the magnitude of *practically identical* or *within experimenal error.* As such, be happy that the theory holds true up to the point that the values are similar and don’t expect it to explain every last digit behind the decimal dot.


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