\(n_{FeCl_2}=\dfrac{50,8}{127}=0,4\left(mol\right)\\ Đặt:n_{FeCl_3}=x\left(mol\right)\\ BTNT\left(Cl\right):n_{HCl}=0,4.2+x.3=0,8+3x\left(mol\right)\\BTNT\left(H\right):n_{H_2O}.2=n_{HCl}.1\\ \Rightarrow n_{H_2O}=0,4+1,5x\left(mol\right)\\BTKL:m_X+m_{HCl}=m_{muối}+m_{H_2O}\\\Rightarrow108,8+\left(0,8+3x\right).36,5=50,8+162,5x+\left(0,4+1,5x\right).18\\ \Rightarrow x=1\\ \Rightarrow m_{FeCl_3}=1.162,5=162,5\left(g\right)\)