Why is CH3CH2NH3Cl acidic?
In short

$\ce{CH3CH2NH3Cl}$ is acidic because it is formed from a strong acid ($\ce{HCl}$) and a weak base ($\ce{CH3CH2NH2}$).



Elaborated

Notice that this compound is ionic, comprising $\ce{CH3CH2NH3+}$ cation and $\ce{Cl-}$ anion.

I mentioned that $\ce{CH3CH2NH2}$ is weak, meaning that this reaction is reversible:

$$\ce{CH3CH2NH2 + H2O &lt;=&gt; CH3CH2NH3+ + OH-}\tag1$$

In an acidic environment, we can rewrite it as:

$$\ce{CH3CH2NH2 + H3O+ &lt;=&gt; CH3CH2NH3+ + H2O}\tag2$$

Therefore, when $\ce{CH3CH2NH3Cl}$ dissolves in water, there would be initially an equal amount of $\ce{CH3CH2NH3+}$ and $\ce{Cl-}$ in terms of number of moles.

Using equation $(2)$, we know that $\ce{CH3CH2NH3+}$ will react with water reaching an acidic equilibrium.

Note that there is no $\ce{OH-}$ to start with (very little in reality), so equation $(1)$ is not applicable.

Therefore, the following species would be present:


$\ce{CH3CH2NH3+}$
$\ce{CH3CH2NH2}$
$\ce{H2O}$
$\ce{H3O+}$
$\ce{Cl-}$


Now it is apparent that $\ce{H3O+}$ makes it acidic.