\(\begin{array}{l} n_{H_2}=\dfrac{6,72}{22,4}=0,3\ (mol)\\ PTHH:\\ 2Al+6HCl\to 2AlCl_3+3H_2\uparrow\ (1)\\ Al_2O_3+6HCl\to 2AlCl_3+3H_2O\ (2)\\ Theo\ pt\ (1):\ n_{Al}=\dfrac{2}{3}n_{H_2}=0,2\ (mol)\\ \Rightarrow m_{Al}=0,2\times 27=5,4\ (g).\\ \Rightarrow m_{Al_2O_3}=15,6-5,4=10,2\ (g)\\ \Rightarrow n_{Al_2O_3}=\dfrac{10,2}{102}=0,1\ (mol)\\ \Rightarrow \sum n_{AlCl_3}=n_{Al}+2n_{Al_2O_3}=0,2+2\times 0,1=0,4\ (mol)\\ \Rightarrow m_{AlCl_3}=0,4\times 133,5=53,4\ (g)\end{array}\)