The aqueous solution of ${\mathrm{FeCl}}_3$ is acidic due to

${\mathrm{FeCl}}_3$  on hydrolysis forms weak base $\mathrm{Fe}{\left(\mathrm{OH}\right)}_3$ and strong acid HCl.

This is called cationic hydrolysis. Due to the presence of ${\mathrm{H}}^{+}$ions solution is acidic.