Ferric chloride is applied to stop bleeding because

${\mathrm{Cl}}^{-}$ ions cause coagulation of blood.

${\mathrm{FeCl}}_3$ reacts with the constituents of blood which is a positively charged sol.

${\mathrm{Fe}}^{3+}$ ions coagulate blood which is a negatively charged sol.

Blood absorbs  ${\mathrm{FeCl}}_3$ and forms a complex